Update on Pollen Thermotolerance

Pollen Development at High Temperature: FromAcclimation to Collapse1[OPEN]

Ivo Rieu*, David Twell, and Nurit Firon

Department of Molecular Plant Physiology, Institute for Water and Wetland Research, Radboud University,6500 GL Nijmegen, The Netherlands (I.R.); Department of Genetics, University of Leicester, Leicester LE1 7RH,United Kingdom (D.T.); and Department of Vegetable Research, Institute of Plant Sciences, AgriculturalResearch Organization, The Volcani Center, Bet Dagan 50250, Israel (N.F.)

ORCID IDs: 0000-0001-8575-0959 (I.R.); 0000-0003-0483-1461 (D.T.).

The seeds and fruits derived from the sexual repro-duction of flowering plants constitute the major part ofthe human diet. Our capacity to generate sufficient cropyield is increasingly compromised by human popula-tion expansion, competition for land use, biodiversityloss, and global climate change. Hot days and heatwaves are predicted to increase in frequency and in-tensity in many temperate regions in the coming de-cades as a consequence of global warming (Pachauriet al., 2014). Exposure to high temperature episodesoften coincides with the reproductive phase of the plantlife cycle. As pollen development and functioning areamong the most heat-sensitive processes that impactupon plant fertility, it is crucial to understand themechanisms and processes underlying heat-relatedmale sterility in order to maintain food security.

Sexual plant reproduction in flowering plants in-volves two central processes: meiosis, which rearrangesthe genes and reduces the number of chromosomes;and fertilization, which restores the diploid chromo-some number. In between these two, haploid sporesdevelop into multicellular gametophytes, which pro-duce the male or female gametes. Development ofthe male gametophyte (pollen) has been shown to besensitive to environmental fluctuations and subopti-mal conditions, thereby limiting sexual reproduction(Iwahori, 1965; Schoper et al., 1987; Peet et al., 1998;Dupuis andDumas, 1990; Ahmed et al., 1992; Kim et al.,2001). Pollen is formed inside the anther locules fromdiploid pollenmother cells that undergomeiosis to giverise to a tetrad of four haploid microspores surroundedby locular fluid. After release from the tetrad, the free

microspores enlarge and divide asymmetrically (pollenmitosis I) to form a larger vegetative cell and a smallergenerative cell. The generative cell is then engulfed bythe vegetative cell and undergoes a second mitosis(pollen mitosis II), either before pollen is released fromthe anther or during pollen tube growth, to form twosperm cells (McCormick, 2004). During the differenti-ation of the pollen mother cells, the innermost antherwall layer forms the tapetum (Goldberg et al., 1993).This tissue is metabolically active, especially at earlymicrospore stage, providing the developing micro-spores with carbohydrates, nutrients, enzymes, andcompounds required for the synthesis of the outerpollen wall (exine). Development of the tapetum istightly coordinated with microspore development andits degeneration begins shortly after microspores are

1 This work was supported by the European Commission (MarieCurie Initial TrainingNetwork FP7: Solanaceae Pollen Thermotolerance/SPOT-ITN, grant no. 289220).

* Address correspondence to i.rieu@science.ru.nl.The author responsible for distribution of materials integral to the

findings presented in this article in accordance with the policy de-scribed in the Instructions for Authors (www.plantphysiol.org) is: IvoRieu (i.rieu@science.ru.nl).

I.R., D.T., and N.F. wrote the article.[OPEN] Articles can be viewed without a subscription.www.plantphysiol.org/cgi/doi/10.1104/pp.16.01644

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released from the tetrad. The correct functioning of thetapetum and its timely degradation are essential forpollen development (Parish and Li, 2010).

One of the abiotic conditions with the most impact onpollen development is high temperature. Plants aresessile organisms, inevitably exposed to ambient tem-peratures throughout their life cycle and can overheatrelative to their environment due to direct absorbanceof solar radiation. High temperatures can change thestructure of biomolecules, such asDNA, RNA, proteins,and lipids, which in turn can affect basic metabolicprocesses like translation, photosynthesis, respiration,and redox regulation (Bokszczanin et al., 2013). At or-ganismal level, this leads to disturbance of growth anddevelopment, with harmful effects often manifestingthemselves only after transition to the reproductivephase. Pollen heat sensitivity is a conserved featureamong diverse plant species, including monocots anddicots, and occurs under various high temperature re-gimes, for example, short heat shock or prolongedgrowth under mildly elevated day and/or night tem-peratures (Mesihovic et al., 2016). The sensitivity variesover the course of pollen development, with laterstages, after pollen mitosis, being relatively heat tol-erant. Medium high-temperature stress may disturbmeiosis, but peak sensitivity occurs from meiosis topollen mitosis I (i.e. at microspore stage), which is thefocus of this work.

The development of pollen after exposure to heatstress at the microspore stage has not been described indetail but includes abortion of microspores as well asfailure at later stages, leading to a reduction in thenumber of pollen grains at anthesis and the proportionof mature pollen grains that is viable and able to ger-minate (Mesihovic et al., 2016). The fact that high-temperature stress may result in a mixed populationof both dead and perfectly viable pollen within thesame anther locule has recently been explained with amodel where initially small differences between mi-crospores in metabolic performance or developmentalprogression are amplified by competition for nutrientsin the locular fluid (Carrizo García et al., 2017). Notably,pollen injury is often accompanied by aberrations intapetum development (hypertrophy) or morphologyand alterations in the timing of tapetum degeneration(Iwahori, 1965; Saini et al., 1984; Ahmed et al., 1992;Kim et al., 2001; Suzuki et al., 2001; Abiko et al., 2005;Oshino et al., 2007; Djanaguiraman et al., 2013; Harsantet al., 2013).

While elevated temperatures may elicit acclimationresponses that permit pollen development under re-stricted heat stress conditions, physiological injuryleading to failure of pollen development and function-ing occurs at higher temperature stress. The balancebetween acclimation and collapse thus depends on theheat regime experienced as well as the levels of basaland acquired thermotolerance. Here, we discuss thecurrent understanding of heat acclimation responsesand heat injury during microspore development. Ther-motolerance mechanisms of mature and germinating

pollen as well as vegetative tissues have been discussedelsewhere (Mittler et al., 2012; Bokszczanin et al., 2013;Tunc-Ozdemir et al., 2013; Burke and Chen, 2015).

ACCLIMATION

Data accumulated over the past few decades indicatethat pollen and the surrounding anther tissues respondto an increase in temperature at the transcriptome,proteome, and metabolome levels, similar to otherplant cell types. Several heat responses that have beencharacterized as adaptive in vegetative tissues werealso found to occur in these reproductive tissues. Inrecent years, experimental evidence for a role of theseresponses in maintaining physiological homeostasisduring pollen development at high temperature hasemerged.

Protein Homeostasis in the Cytosol: The HeatShock Response

One of the main damaging effects of high tempera-ture results from changes in protein structure. This mayinterfere with protein function, and if more hydropho-bic regions are exposed, proteins can aggregate andbecome cytotoxic. Failure to prevent the accumulationand aggregation of misfolded proteins may eventuallylead to cell death. To counteract these effects, the ex-pression of heat shock protein (HSP) chaperones isinduced at high temperature in a process known as theheat shock response (HSR). HSPs accumulate in thecytoplasm and organelles to stabilize, resolubilize, andrefold proteins (Vierling, 1991; Hartl et al., 2011). Re-cently, it was demonstrated that small HSPs are im-portant for heat tolerance in Arabidopsis. Two of themost abundant classes of sHSPs (C1 and CII) wereshown to interact with and to protect an overlapping setof heat sensitive proteins involved in translation initi-ation (eIF4A) and elongation (eEF1B), together withHSP101 (McLoughlin et al., 2016). Underlying the HSRis a network of heat stress transcription factors (HSFs)that bind to a palindromic DNA sequence, the heat shockelement, to induce the expression of heat-responsivegenes (Scharf et al., 2012; Ohama et al., 2017).

High-temperature induction of HSF and HSP genesin developing anthers, microspores, and pollen hasbeen reported for different species (Frank et al., 2009;Giorno et al., 2010; Bita et al., 2011; Zhang et al., 2014; Liet al., 2015). Furthermore, proteins of different types ofHSPs (i.e. belonging to diverse families, like sHSP,HSP70, HSP90, and HSP100) accumulate in developinganthers and pollen grains after a short period of high-temperature stress (Frova et al., 1989, 1991; Jagadishet al., 2010; Chaturvedi et al., 2015), which points to acapacity for both tissues to activate “classical” ther-motolerance mechanisms. A recent study in tomato(Solanum lycopersicum) has shown that induction ofHSR protects microspores from high temperature(Fragkostefanakis et al., 2016b). One of the main HSFs

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regulating the HSR is HSFA2, which forms a “super-activator complex” with HSFA1 proteins (Scharf et al.,2012). Knockdown of HSFA2 resulted in increasedsensitivity of developing tomato pollen to a shortperiod of high temperature (Fragkostefanakis et al.,2016b). The effect of reduced levels of HSPs on pollenthermotolerance has not been tested, but members ofthe Bcl-2-associated athanogene (BAG) family havebeen shown to be involved in pollen thermotolerance(Doukhanina et al., 2006). BAG proteins are cocha-perones involved in recruiting HSPs to client pro-teins; they are expressed in developing tomato pollenunder heat stress, and their expression may be undercontrol ofHSFA2 (Frank et al., 2009; Fragkostefanakiset al., 2015).Taken together, various HSFs and HSPs are induced

in anthers and microspores by high temperature, andgenetic studies confirm that they play an active role inprotecting developing pollen against heat stress.

Protein Homeostasis in the ER: The UnfoldedProtein Response

Upon exposure to elevated temperatures, a secondset of genes, including ones that encode chaperones, isinduced to protect cells against toxic levels of unfoldedproteins in the endoplasmic reticulum (ER) (Howell,2013). Protein folding is an essential function of the ER,involving the guidance of polypeptides through severalmodification steps to reach their desired conformation.The folded protein may remain in the endomembranesystem, be targeted to the cell membrane, or be se-creted. A polypeptide that is not glycosylated is foldedby the luminal binding protein (BiP)-Hsp70/DnaJ andHsp90 chaperone machineries, which are favored bythe highly oxidizing environment of the ER. Proteindisulfide isomerases facilitate formation of disulfidebonds, which confer structural stability to the protein.Alternatively, polypeptides are glycosylated at ER en-try through N-linked glycosylation, followed by disul-fide bond formation. N-linked glycosylation providesthe sugar molecules that form the key ligand for thelectin-like chaperones calreticulin and calnexin. An ex-cess of misfolded proteins in the ER leads to enhancedexpression of a number of the components of the ERprotein folding machinery, in a process known as theunfolded protein response (UPR). Two pathways areinvolved in eliciting this response; one is dependent onrelease of bZIP28/bZIP17 from the ER membrane andthe other on alternative splicing of bZIP60 by IRE1(Deng et al., 2011; Srivastava et al., 2013). However,bZIP60 is able to heterodimerize with bZIP28 andbZIP17, indicating that the two arms of the UPR sig-naling pathways merge. Several of the UPR genes areinduced upon heat and seedlings of a bZIP28 knockoutmutant were shown to be sensitive to high temper-atures, suggesting an essential role of the UPR ingeneral heat stress response and thermotolerance(Fragkostefanakis et al., 2016a).

The main components of the ER protein foldingmachinery, such as calreticulin, calnexin, and BiP, arepresent throughout microspore and pollen develop-ment (Honys and Twell, 2004; Sheoran et al., 2006;Chaturvedi et al., 2013). Moreover, the UPR is essentialfor regular pollen development, given that severalmutants in the pathway have male gametophyte de-fective or lethal phenotypes (Fragkostefanakis et al.,2016a). During or shortly after a heat shock or long-term exposure to mild heat, the UPR is up-regulatedin male reproductive tissues at transcript and proteinlevel (Frank et al., 2009; Bita et al., 2011; Chaturvediet al., 2015; Li et al., 2015; Fragkostefanakis et al.,2016b), suggesting the UPR has a function in acclima-tion of developing pollen to heat. Experimental sup-port for this hypothesis was recently delivered,through the analysis of an ire1a ire1b double knockoutmutant, which inactivates the RNA-splicing arm of theUPR signaling pathway. The mutant was found to befertile at room temperature, but male sterile at slightlyelevated temperatures, showing reduced viability ofmature pollen and altered pollen coat composition(Deng et al., 2016). Interestingly, conditional malesterility in the mutant was a sporophytic trait andwhen the double mutant was grown at elevated tem-perature, defects appeared in the structure of the ta-petum. It is conceivable that increased protein foldingcapacity of the tapetal ER is essential for functioning athigh temperature, given the high secretory activity ofthe tapetum.

Reactive Oxygen Species Scavenging

Part of the cellular damage by high temperature isascribed to accumulation of reactive oxygen species(ROS). ROS are produced during aerobic metabolism,deriving from different cellular compartments, includ-ing mitochondria, chloroplasts, peroxisomes, and theapoplast (Mittler et al., 2004). In addition to beingtoxic metabolic by-products, ROS also act as signalingmolecules mediating stress responses (Baxter et al.,2014). Cells possess extensive ROS scavenging anddetoxification machinery, which consists of enzymessuch as catalase, ascorbate peroxidase (APX), and su-peroxide dismutase, as well as antioxidant substanceslike ascorbic acid and flavonoids (Mittler et al., 2004).Many of the ROS scavenging-related genes are re-sponsive to ROS levels, which results in a regulatedbalance between production and scavenging understeady state conditions. Exposure to high temperaturecan disturb this balance, and a number of studies invegetative tissues and cell types show that heat rapidlyleads to accumulation of ROS, resulting in a secondary,oxidative stress. To cope with the excess amount of ROSupon heat, the expression of ROS scavengers and levelsof antioxidants are rapidly up-regulated by heat(Driedonks et al., 2015). The fact that increased anti-oxidative activity increases vegetative tissue/organthermotolerance in different plant species indicates

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that this response is adaptive (Gupta et al., 1993; Singhand Grover, 2008; Chen et al., 2013).

ROS play an important role in the formation of viablepollen. The programmed cell death of tapetal cellsduring microspore development involves ROS action.ROS levels in anthers were shown to peak during ta-petum degeneration and at pollen maturity in Arabi-dopsis (Arabidopsis thaliana) and rice (Oryza sativa; Huet al., 2011; Xie et al., 2014; Yi et al., 2016). Accordingly,a proteomic study detected catalase (CAT3) and gluta-thione reductase (GR1) in developing pollen (Chaturvediet al., 2013). Pollen and tapetum cells have also beenshown to accumulate large numbers ofmitochondria andshow high rates of respiration (Lee and Warmke, 1979;Selinski and Scheibe, 2014). Under high temperatures,this might be expected to cause a dramatic increase inROS. Indeed, long-term mild heat has been shown toincrease ROS levels in sorghum pollen (Djanaguiramanet al., 2014). In rice, heat induced the expression of severalROS-related genes in florets (Zhang et al., 2012; Zhanget al., 2014), andGST andAPXgeneswere upregulated indeveloping tomato anthers and pollen (Frank et al., 2009;Bita et al., 2011; Fragkostefanakis et al., 2016b). Theup-regulation of GST and APX genes in response to heatis reflected by increased levels of the correspondingproteins (Chaturvedi et al., 2015). These data point to-ward the accumulation of ROS in anthers and pollenupon heat, although APX genes are also responsive toheat in a ROS-independent manner, due to the presenceof heat shock elements in their promoters (Driedonkset al., 2015). There is no direct evidence that enhancedROS scavenging activity supports pollen developmentunder high temperature conditions. However, excessiveROS at the late microspore stage in rice mads3 led totapetal dysfunction and pollen abortion (Hu et al., 2011;Luo et al., 2013). Conversely, Arabidopsis and rice mu-tants with reduced amounts of ROS fail to activate thetimely onset of tapetum programmed cell death, leadingto pollen failure (Xie et al., 2014; Yi et al., 2016). Thus, thetight regulation of ROS content is essential for the pro-duction of viable pollen, making it likely that increasedscavenging activity contributes to heat acclimation.Further support for this hypothesis is provided by ex-periments in wheat and rice, which suggest increasedpollen viability upon heat treatment after exogenousapplication of antioxidants (Kumar et al., 2014; Fahadet al., 2016).

Distinguishing Acclimation from Injury

Untargeted “omics” studies have shown that hightemperature elicits a suite of transcriptomic, proteomic,and metabolomic changes in developing anthers andpollen, many of which are not directly associated withthe well-characterized heat acclimation responses de-scribed above (transcriptomic: Abiko et al., 2005; Oshinoet al., 2007; Endo et al., 2009; Frank et al., 2009; Bita et al.,2011; Zhang et al., 2012; Min et al., 2014; Zhanget al., 2014; Li et al., 2015; Fragkostefanakis et al., 2016b;

proteomic: Jagadish et al., 2010; Chaturvedi et al., 2015;metabolomic: Li et al., 2015; Fragkostefanakis et al.,2016b). Although some of these changes may be passiveconsequences of heat injury and play no role in accli-mation, it seems likely that others have adaptive value.

Functional data would allow differentiation of thetwo categories. For example, transcripts related to eth-ylene and abscisic acid (ABA) signaling accumulate indeveloping tomato pollen and in rice florets after ashort heat episode (Frank et al., 2009; Bita et al., 2011;Zhang et al., 2012; Zhang et al., 2014). Pollen of anethylene insensitive tomato mutant was found to bemore sensitive to chronic mild heat stress, whilechemical induction of ethylene production prior to ashort heat stress treatment improved pollen thermo-tolerance and application of an ethylene inhibitor re-duced it (Firon et al., 2012). Together, these resultsmakea strong case for ethylene as an acclimation factor. ForABA, the relationship is less clear. In rice florets ex-posed to reoccurring heat stress for 5 d, ABA concen-trations were higher than under control conditions(Tang et al., 2008). Although it has been shown thatABA contributes to heat acclimation of vegetative or-gans (Larkindale and Huang 2005), this has not beenshown for reproductive tissue. In fact, ABA accumu-lation seems to negatively affect pollen development(Parish et al., 2012). Several other studies have noted thedown-regulation of ribosomal proteins and transcripts(Abiko et al., 2005; Oshino et al., 2007; Jagadish et al.,2010; Bita et al., 2011). It has been suggested that a re-duction in protein synthesis rate with heat might act toalleviate the stress caused by misfolded proteins in thecytoplasm and ER (Ruberti and Brandizzi, 2014), butthis has not been tested.

As an alternative approach to identifying adaptiveheat responses, dependency of heat-induced changeson signaling pathways associated with acclimationmight be taken as an indication. HSF transcriptionfactors are the main regulators of the HSR, acting up-stream of many HSP responses (Scharf et al., 2012).Fragkostefanakis et al. (2016b) found that most heat-responsive genes in anthers carried the HSF targetedheat shock element cis-element in their promoters. Anumber of these responses were shown to depend onHSFA2 activity, and interestingly, the same was truefor some metabolomic changes, such as accumulationof the nonprotein amino acid GABA, which is thoughtto have a protective role under oxidative stress(Kinnersley and Turano, 2000). Thus, a significantnumber of responses may contribute to heat accli-mation, even though their specific roles are largelyunknown, requiring further research as discussed inthe “Perspective” section.

COLLAPSE

Despite the acclimation responses, pollen develop-ment is adversely affected at temperatures at whichmost other plant tissues and processes show limited

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effects. In general, developing pollen and ovules expe-rience high temperature simultaneously, but the formeris more sensitive to heat (Gross and Kigel, 1994; Peetet al., 1998; Oshino et al., 2007). The sequence of eventsthat lead to pollen failure under high temperature re-mains to be determined, and the tissue(s) that areprimarily affected have not been unequivocally estab-lished; in principle, high temperature might directlyaffect developing microspores, the supporting sporo-phytic tissues, or both.

Carbon Starvation

The importance of carbohydrate partitioning understress conditions has been widely documented (Ruanet al., 2010). However, as photosynthesis and overallplant growth are not significantly affected by relativelyshort or mild high temperature regimes that impairpollen development (Sharkey, 2005; Mathur et al.,2014), carbohydrate supply at source tissues is notlikely to be limiting in this case. On the other hand,there are indications that carbohydrate metabolismand unloading in the anther and pollen play a role.Starch and soluble sugar levels are finely regulatedduring pollen development. Under normal conditions,Suc concentrations remain fairly stable, but starch ac-cumulates to reach a peak after pollen mitosis I, oftenfollowed by gradual breakdown into soluble sugars atanthesis (Pacini et al., 2006; Pressman et al., 2012). Sucand hexoses serve as energy sources for developmentand pollen germination and are also thought to act asosmolytes (Pressman et al., 2012). Under mild heatstress, Suc content is reduced in young microsporesand starch buildup in binucleate pollen is lower.Consequently, soluble sugar content is also lower atanthesis (Pressman et al., 2002; Firon et al., 2006; Satoet al., 2006; Jain et al., 2007). A relationship betweencarbohydrate content and pollen viability is supportedby findings that more tolerant genotypes were betterable to maintain pollen starch and sugar levels thansensitive genotypes (Pressman et al., 2002; Firon et al.,2006).Suc is the main form of photosynthetic assimilate

exported from source tissue. As with the microspores,its unloading and uptake in symplastically isolated cellsdepends largely on the activity of cell wall acid inver-tase (CWIN; De Storme and Geelen, 2014). CWIN ac-tivity is maintained at high levels in tapetal cells anddeveloping pollen (Goetz et al., 2001; Pressman et al.,2012), and in several studies, heat stress was shown tolower CWIN transcript levels and enzyme activity indeveloping microspores and anthers (Pressman et al.,2006; Sato et al., 2006; Jain et al., 2007; Kaur et al., 2015).In accordance with the potential role of CWIN, aheat tolerant rice variety had relatively high CWINexpression under mild heat (Li et al., 2015), whilethe silencing of CWIN genes in tomato and tobacco(Nicotiana tabacum) significantly reduced pollen via-bility (Goetz et al., 2001; Li et al., 2015; Zanor et al.,2009). Similarly, the expression of vacuolar invertase

was down-regulated by continuous mild heat in mei-otic and microspore stage anthers (Sato et al., 2006),and it has been shown that silencing of vacuolar in-vertase in reproductive organs can lead to reducedpollen viability (Wang and Ruan, 2016).

Thus, it could be speculated that carbohydrate de-pletion in developing pollen may be the result of de-creased hexose supply by the tapetum or reduceduptake by the pollen at high temperatures. Developingpollen and tapetum cells seem to have unusually highenergy demands as indicated by their high numbers ofmitochondria (Lee and Warmke, 1979; Selinski andScheibe, 2014); depletion in carbohydrate reservesmight thus affect tapetum and pollen more than othercells. However, experimental proof for the carbohy-drate deficiency hypothesis is still lacking: Studieshave not yet clarified whether reduced carbohydratelevels at elevated temperatures cause pollen abortionor merely reflect the consequence of reduced pollenfunctioning.

Other Types of Heat Injury

Other putative physiological injuries have beensuggested to play an intermediary role in causingpollen sterility in response to heat. Increased proteinmisfolding and ROS accumulation are describedabove and there are reasons to believe that these mightreach levels beyond protection capacity faster in an-thers and pollen than elsewhere in the plant. Heatleads to irregular ER structure in tapetal cells and indeveloping pollen (Suzuki et al., 2001; Oshino et al.,2007), which might point to an overload of the UPR.Classical sets of HSPs were found to be hardly inducedin mature or germinating pollen upon heat shock(Müller and Rieu, 2016). At earlier stages of pollendevelopment, HSFs and HSPs are induced by heat, butto a lesser extent than in vegetative tissue (Frovaet al., 1989; Gagliardi et al., 1995; Volkov et al., 2006;Fragkostefanakis et al., 2016b), which may contributeto higher heat stress sensitivity of developing pollen. Ithas been suggested that microspores compete for nu-trients in the anther locule, especially under subopti-mal growth conditions (Carrizo García et al., 2017).While in vegetative plant tissues, HSPs accumulateto become among the most abundant proteins uponhigh-temperature exposure (Vierling, 1991), resourcescarcity might prevent microspores from investingheavily in protective measures. Furthermore, the rel-atively high numbers of mitochondria in developingpollen and tapetal cells might produce dispropor-tionate levels of reactive oxygen species in response toheat, as observed in sorghum pollen (Djanaguiramanet al., 2014). Interestingly, high-temperature defects indeveloping pollen and tapetum share some similari-ties with those observed in plants showing cytoplas-mic male sterility, a phenomenon thought to be linkedtomitochondrial dysfunction and ROS activity (Müllerand Rieu, 2016).

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Other molecules are also affected by high tempera-ture. Pro acts as a compatible solute in osmoprotectionand accumulates in response to different abiotic stresses(Krasensky and Jonak, 2012). Pro is a key factor forpollen viability (Lansac et al., 1996), and in severalspecies, levels decrease in pollen under high tempera-ture regimes that disturb pollen development (Mutterset al., 1989; Tang et al., 2008). Interestingly, the ex-pression of Pro transporter 1mRNA was reduced underthese conditions. This might suggest that Pro is incor-porated into pollen grains from the locular fluid ratherthan being produced by pollen itself and may be

reduced at high temperature (Sato et al., 2006). Lipidsare also affected by heat. The type of lipids in cellularmembranes and their saturation level are importantdeterminants of membrane fluidity and functioning. Inbarley (Hordeum vulgare), long-term growth at mildlyelevated temperature led to alterations in phospholipidsaturation in pollen (Prasad and Djanaguiraman, 2011).This in turn might make the membranes more suscep-tible to ROS damage. Finally, the levels of two phyto-hormones important for pollen development seem to beaffected by high temperature. Auxin levels in anthersare reduced by high temperature in Arabidopsis, rice,

Figure 1. Effects of heat related to acclimation or collapse of developing microspores. Genes involved are indicated betweenbrackets. Resource limitation is hypothesized to impose a trade-off between acclimation and development (see “Perspective”section).

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and barley, in contrast to the response of vegetativetissues (Tang et al., 2008; Sakata et al., 2010). Interest-ingly, exogenous application of auxin improved toler-ance of developing pollen to continuous mild heatstress in barley (Sakata et al., 2010). Tang et al. (2008)found that bioactive gibberellin (GA) content also de-creased in mature anthers under heat stress in rice.Furthermore, in an independent study of rice, the set oftapetum-specific genes that were downregulated undercontinuous mild heat stress was enriched for GA-responsive genes (Endo et al., 2009). The GA deficiency/insensitivity phenotype is notably similar to the heatphenotype, sharing features such as abnormal tapetaldevelopment, delayed or inhibited programmed celldeath, and developmental arrest at microspore stage(Jacobsen and Olszewski, 1991; Aya et al., 2009).Moreover, one class of GA target genes expressed in thetapetum are the invertases described above (Proelset al., 2006). Putatively related to changes in GA signal,it was recently found that mild heat reduces the ex-pression of B-class MADS box genes and that partialdown-regulation of these genes mimics the heat phe-notype, including reduced pollen viability (Mülleret al., 2016).

PERSPECTIVE

It is clear that developing anthers and pollen have thecapacity for acclimation to high temperature, and fur-ther research may reveal many more heat responses tobe adaptive than currently thought. Collectively, theseresponses permit the production of viable pollen at

certain levels of heat stress (Fig. 1). What remains un-clear is how mild heat stress results in defective pollendevelopment and why developing microspores andpollen are heat sensitive compared to other plant tissues(Box 1; Fig. 1). Does the latter response arise as the lesserof two evils, i.e. does inherent energy or nutrient limi-tation in the anther locule prevent microspores deviat-ing from a fixed developmental path toward strongacclimation?

Based on the fundamental influence of heat on allmolecules, it is likely that pollen failure is not the resultof a single primary effect, propagated as a linear seriesof consequences, but of a combination of effects thatbehave synergistically. The finding that heat tolerancein vegetative tissues can be improved by targetingdifferent physiological processes supports this hy-pothesis (Singh and Grover, 2008). But how can weproceed to identify what injuries are causally linked tothe pollen phenotype? First, it will be essential to gen-erate more specific hypotheses by applying analyseswith increased temporal and spatial resolution. The factthat both tapetum and microspores/pollen constituteonly part of the anther reduces the resolving powerof many studies that sample whole anthers or evenflowers. Furthermore, the rapid and inherently asyn-chronous development of cells of interest in the antherrestricts temporal resolution (Carrizo García et al.,2017). Promising new expression profiling methodsinclude various types of immunopurification-basedtranscript capturing in combination with a cell- orstage-specific activation (Bailey-Serres, 2013). Simi-larly, recently developed techniques allow for cell-specific metabolome analyses (Fessenden, 2016). Further

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opportunities exist in examining the similarities betweenthe effects of heat and other abiotic stresses, such ascold, drought, and high salinity on male gametophytedevelopment (De Storme and Geelen, 2014; Das et al.,2015; Sharma and Nayyar, 2016). To test the (new)hypotheses generated, the phenotypic effect of mim-icking the injury could be suggestive, as applied toinvertases, B-classMADS box genes, andGA signaling.However, complementation studies, where specificdefects are counteracted using pharmacological or ge-netic approaches, are necessary to establish cause-and-effect relationships. The auxin rescue experiment inbarley by Sakata et al. (2010) provides an instructiveexample, and it will be interesting to see whether theirfindings will extend to other species. Applying this

principle, it would be logical to determine whether, forexample, increased levels of invertases in the devel-oping tapetum or pollen are beneficial for thermotol-erance. Studies into the genetic basis of natural andartificial variation have also been highly effective indissecting other plant-environment interactions, so thisstrategy holds promise for identifying major determi-nants of pollen thermotolerance. It has been suggestedthat pollen heat sensitivity could be an adaptationitself, preventing investment in reproduction underadverse conditions (Müller and Rieu, 2016). If true, onecould expect less heat sensitivity in dioecious speciesand, counterintuitively, higher pollen thermotolerancein species or genotypes originating from moderatetemperature habitats.Received October 24, 2016; accepted February 22, 2017; published February 28,2017.

LITERATURE CITED

Abiko M, Akibayashi K, Sakata T, Kimura M, Kihara M, Itoh K, AsamizuE, Sato S, Takahashi H, Higashitani A (2005) High-temperature in-duction of male sterility during barley (Hordeum vulgare L.) anther de-velopment is mediated by transcriptional inhibition. Sex Plant Reprod18: 91–100

Ahmed FE, Hall AE, Demason DA (1992) Heat injury during floral de-velopment in cowpea (Vigna unguiculata, Fabaceae). Am J Bot 79: 784–791

Aya K, Ueguchi-Tanaka M, Kondo M, Hamada K, Yano K, Nishimura M,Matsuoka M (2009) Gibberellin modulates anther development in ricevia the transcriptional regulation of GAMYB. Plant Cell 21: 1453–1472

Bailey-Serres J (2013) Microgenomics: genome-scale, cell-specific moni-toring of multiple gene regulation tiers. Annu Rev Plant Biol 64: 293–325

Baxter A, Mittler R, Suzuki N (2014) ROS as key players in plant stresssignalling. J Exp Bot 65: 1229–1240

Bita CE, Zenoni S, Vriezen WH, Mariani C, Pezzotti M, Gerats T (2011)Temperature stress differentially modulates transcription in meioticanthers of heat-tolerant and heat-sensitive tomato plants. BMC Ge-nomics 12: 384

Bokszczanin KL, Fragkostefanakis S; Solanaceae Pollen ThermotoleranceInitial Training Network (SPOT-ITN) Consortium (2013) Perspectiveson deciphering mechanisms underlying plant heat stress response andthermotolerance. Front Plant Sci 4: 315

Burke JJ, Chen J (2015) Enhancement of reproductive heat tolerance inplants. PLoS One 10: e0122933

Carrizo García C, Nepi M, Pacini E (2017) It is a matter of timing: asyn-chrony during pollen development and its consequences on pollenperformance in angiosperms-a review. Protoplasma 254: 57–73

Chaturvedi P, Doerfler H, Jegadeesan S, Ghatak A, Pressman E, CastillejoMA, Wienkoop S, Egelhofer V, Firon N, Weckwerth W (2015) Heattreatment-responsive proteins in different developmental stages of to-mato pollen detected by targeted mass accuracy precursor alignment(tMAPA). J Proteome Res 14: 4463–4471

Chaturvedi P, Ischebeck T, Egelhofer V, Lichtscheidl I, Weckwerth W(2013) Cell-specific analysis of the tomato pollen proteome from pollenmother cell to mature pollen provides evidence for developmentalpriming. J Proteome Res 12: 4892–4903

Chen S, Liu A, Zhang S, Li C, Chang R, Liu D, Ahammed GJ, Lin X (2013)Overexpression of mitochondrial uncoupling protein conferred resis-tance to heat stress and Botrytis cinerea infection in tomato. Plant PhysiolBiochem 73: 245–253

Das P, Nutan KK, Singla-Pareek SL, Pareek A (2015) Understanding sa-linity responses and adopting ‘omics-based’ approaches to generatesalinity tolerant cultivars of rice. Front Plant Sci 6: 712

Deng Y, Humbert S, Liu JX, Srivastava R, Rothstein SJ, Howell SH (2011)Heat induces the splicing by IRE1 of a mRNA encoding a transcriptionfactor involved in the unfolded protein response in Arabidopsis. ProcNatl Acad Sci USA 108: 7247–7252

1974 Plant Physiol. Vol. 173, 2017

Rieu et al.

Dow

nloaded from https://academ

ic.oup.com/plphys/article/173/4/1967/6116104 by guest on 24 August 2021

Deng Y, Srivastava R, Quilichini TD, Dong H, Bao Y, Horner HT, HowellSH (2016) IRE1, a component of the unfolded protein response signalingpathway, protects pollen development in Arabidopsis from heat stress.Plant J 88: 193–204

De Storme N, Geelen D (2014) The impact of environmental stress on malereproductive development in plants: biological processes and molecularmechanisms. Plant Cell Environ 37: 1–18

Djanaguiraman M, Prasad PVV, Boyle DL, Schapaugh WT (2013) Soy-bean pollen anatomy, viability and pod set under high temperaturestress. J Agron Crop Sci 199: 171–177

Djanaguiraman M, Prasad PVV, Murugan M, Perumal R, Reddy UK(2014) Physiological differences among sorghum (Sorghum bicolor L. Moench)genotypes under high temperature stress. Environ Exp Bot 100: 43–54

Doukhanina EV, Chen S, van der Zalm E, Godzik A, Reed J, DickmanMB (2006) Identification and functional characterization of the BAGprotein family in Arabidopsis thaliana. J Biol Chem 281: 18793–18801

Driedonks N, Xu J, Peters JL, Park S, Rieu I (2015) Multi-level interactionsbetween heat shock factors, heat shock proteins, and the redox systemregulate acclimation to heat. Front Plant Sci 6: 999

Dupuis I, Dumas C (1990) Influence of temperature stress on in vitrofertilization and heat shock protein synthesis in maize (Zea mays L.)reproductive tissues. Plant Physiol 94: 665–670

Endo M, Tsuchiya T, Hamada K, Kawamura S, Yano K, Ohshima M,Higashitani A, Watanabe M, Kawagishi-Kobayashi M (2009) Hightemperatures cause male sterility in rice plants with transcriptional al-terations during pollen development. Plant Cell Physiol 50: 1911–1922

Fahad S, Hussain S, Saud S, Khan F, Hassan S, Amanullah, Nasim W,Arif M, Wang F, Huang J (2016) Exogenously applied plant growthregulators affect heat-stressed rice pollens. J Agron Crop Sci 202: 139–150

Fessenden M (2016) Metabolomics: Small molecules, single cells. Nature540: 153–155

Firon N, Pressman E, Meir S, Khoury R, Altahan L (2012) Ethylene isinvolved in maintaining tomato (Solanum lycopersicum) pollen qualityunder heat-stress conditions. AoB Plants 2012: pls024

Firon N, Shaked R, Peet MM, Pharr DM, Zamski E, Rosenfeld K, AlthanL, Pressman E (2006) Pollen grains of heat tolerant tomato cultivarsretain higher carbohydrate concentration under heat stress conditions.Sci Hortic (Amsterdam) 109: 212–217

Fragkostefanakis S, Mesihovic A, Hu Y, Schleiff E (2016a) Unfoldedprotein response in pollen development and heat stress tolerance. PlantReprod 29: 81–91

Fragkostefanakis S, Mesihovic A, Simm S, Paupière MJ, Hu Y, Paul P,Mishra SK, Tschiersch B, Theres K, Bovy A, Schleiff E, Scharf KD(2016b) HsfA2 controls the activity of developmentally and stress-regulated heat stress protection mechanisms in tomato male reproduc-tive tissues. Plant Physiol 170: 2461–2477

Fragkostefanakis S, Simm S, Paul P, Bublak D, Scharf KD, Schleiff E(2015) Chaperone network composition in Solanum lycopersicum ex-plored by transcriptome profiling and microarray meta-analysis. PlantCell Environ 38: 693–709

Frank G, Pressman E, Ophir R, Althan L, Shaked R, Freedman M, Shen S,Firon N (2009) Transcriptional profiling of maturing tomato (Solanumlycopersicum L.) microspores reveals the involvement of heat shockproteins, ROS scavengers, hormones, and sugars in the heat stress re-sponse. J Exp Bot 60: 3891–3908

Frova C, Taramino G, Binelli G (1989) Heat-shock proteins during pollendevelopment in maize. Dev Genet 10: 324–332

Frova C, Taramino G, Ottaviano E (1991) Sporophytic and gametophyticheat shock protein synthesis in Sorghum bicolor. Plant Sci 73: 35–44

Gagliardi D, Breton C, Chaboud A, Vergne P, Dumas C (1995) Expressionof heat shock factor and heat shock protein 70 genes during maize pollendevelopment. Plant Mol Biol 29: 841–856

Giorno F, Wolters-Arts M, Grillo S, Scharf KD, Vriezen WH, Mariani C(2010) Developmental and heat stress-regulated expression of HsfA2and small heat shock proteins in tomato anthers. J Exp Bot 61: 453–462

Goetz M, Godt DE, Guivarc’h A, Kahmann U, Chriqui D, Roitsch T (2001)Induction of male sterility in plants by metabolic engineering of thecarbohydrate supply. Proc Natl Acad Sci USA 98: 6522–6527

Goldberg RB, Beals TP, Sanders PM (1993) Anther development: basicprinciples and practical applications. Plant Cell 5: 1217–1229

Gross Y, Kigel J (1994) Differential sensitivity to high temperature of stagesin the reproductive development of common bean (Phaseolus vulgaris L.).Field Crops Res 36: 201–212

Gupta AS, Webb RP, Holaday AS, Allen RD (1993) Overexpression ofsuperoxide dismutase protects plants from oxidative stress (induction ofascorbate peroxidase in superoxide dismutase-overexpressing plants).Plant Physiol 103: 1067–1073

Harsant J, Pavlovic L, Chiu G, Sultmanis S, Sage TL (2013) High tem-perature stress and its effect on pollen development and morphologicalcomponents of harvest index in the C3 model grass Brachypodium dis-tachyon. J Exp Bot 64: 2971–2983

Hartl FU, Bracher A, Hayer-Hartl M (2011) Molecular chaperones in pro-tein folding and proteostasis. Nature 475: 324–332

Honys D, Twell D (2004) Transcriptome analysis of haploid male game-tophyte development in Arabidopsis. Genome Biol 5: R85

Howell SH (2013) Endoplasmic reticulum stress responses in plants. AnnuRev Plant Biol 64: 477–499

Hu L, Liang W, Yin C, Cui X, Zong J, Wang X, Hu J, Zhang D (2011) RiceMADS3 regulates ROS homeostasis during late anther development.Plant Cell 23: 515–533

Iwahori S (1965) High temperature injuries in tomato. IV. Development ofnormal flower buds and morphological abnormalities of flower budstreated with high temperature. J Jpn Soc Hortic Sci 34: 33–41

Jacobsen SE, Olszewski NE (1991) Characterization of the arrest in antherdevelopment associated with gibberellin deficiency of the gib-1 mutantof tomato. Plant Physiol 97: 409–414

Jagadish SVK, Muthurajan R, Oane R, Wheeler TR, Heuer S, Bennett J,Craufurd PQ (2010) Physiological and proteomic approaches to addressheat tolerance during anthesis in rice (Oryza sativa L.). J Exp Bot 61: 143–156

Jain M, Prasad PVV, Boote KJ, Hartwell AL, Jr., Chourey PS (2007) Effectsof season-long high temperature growth conditions on sugar-to-starchmetabolism in developing microspores of grain sorghum (Sorghum bicolorL. Moench). Planta 227: 67–79

Kaur R, Bains TS, Bindumadhava H, Nayyar H (2015) Responses of mung-bean (Vigna radiata L.) genotypes to heat stress: Effects on reproductivebiology, leaf function and yield traits. Sci Hortic (Amsterdam) 197: 527–541

Kim SY, Hong CB, Lee I (2001) Heat shock stress causes stage-specific malesterility in Arabidopsis thaliana. J Plant Res 114: 301–307

Kinnersley AM, Turano FJ (2000) Gamma aminobutyric acid (GABA) andplant responses to stress. Crit Rev Plant Sci 19: 479–509

Krasensky J, Jonak C (2012) Drought, salt, and temperature stress-inducedmetabolic rearrangements and regulatory networks. J Exp Bot 63: 1593–1608

Kumar RR, Goswami S, Gadpayle KA, Singh K, Sharma SK, Singh GP,Pathak H, Rai RD (2014) Ascorbic acid at pre-anthesis modulate thethermotolerance level of wheat (Triticum aestivum) pollen under heatstress. J Plant Biochem Biotechnol 23: 293–306

Lansac AR, Sullivan CY, Johnson BE (1996) Accumulation of free prolinein sorghum (Sorghum bicolor) pollen. Can J Bot 74: 40–45

Larkindale J, Huang BR (2005) Effects of abscisic acid, salicylic acid, eth-ylene and hydrogen peroxide in thermotolerance and recovery forcreeping bentgrass. Plant Growth Regul 47: 17–28

Lee S-LJ, Warmke HE (1979) Organelle size and number in fertile andT-cytoplasmic male-sterile corn. Am J Bot 66: 141–148

Li X, Lawas LMF, Malo R, Glaubitz U, Erban A, Mauleon R, Heuer S,Zuther E, Kopka J, Hincha DK, Jagadish KSV (2015) Metabolic andtranscriptomic signatures of rice floral organs reveal sugar starvation asa factor in reproductive failure under heat and drought stress. Plant CellEnviron 38: 2171–2192

Luo D, et al (2013) A detrimental mitochondrial-nuclear interaction causescytoplasmic male sterility in rice. Nat Genet 45: 573–577

Mathur S, Agrawal D, Jajoo A (2014) Photosynthesis: response to hightemperature stress. J Photochem Photobiol B 137: 116–126

McCormick S (2004) Control of male gametophyte development. Plant Cell(Suppl) 16: S142–S153

McLoughlin F, Basha E, Fowler ME, Kim M, Bordowitz J, Katiyar-Agarwal S,Vierling E (2016) Class I and II small heat shock proteins together withHSP101 protect protein translation factors during heat stress. Plant Physiol172: 1221–1236

Mesihovic A, Iannacone R, Firon N, Fragkostefanakis S (2016) Heat stressregimes for the investigation of pollen thermotolerance in crop plants.Plant Reprod 29: 93–105

Min L, Li Y, Hu Q, Zhu L, Gao W, Wu Y, Ding Y, Liu S, Yang X, Zhang X(2014) Sugar and auxin signaling pathways respond to high-temperaturestress during anther development as revealed by transcript profilinganalysis in cotton. Plant Physiol 164: 1293–1308

Plant Physiol. Vol. 173, 2017 1975

Pollen Development at High Temperature

Dow

nloaded from https://academ

ic.oup.com/plphys/article/173/4/1967/6116104 by guest on 24 August 2021

Mittler R, Finka A, Goloubinoff P (2012) How do plants feel the heat?Trends Biochem Sci 37: 118–125

Mittler R, Vanderauwera S, Gollery M, Van Breusegem F (2004) Reactiveoxygen gene network of plants. Trends Plant Sci 9: 490–498

Müller F, Rieu I (2016) Acclimation to high temperature during pollendevelopment. Plant Reprod 29: 107–118

Müller F, Xu J, Kristensen L, Wolters-Arts M, de Groot PFM, Jansma SY,Mariani C, Park S, Rieu I (2016) High-temperature-induced defects intomato (Solanum lycopersicum) anther and pollen development are as-sociated with reduced expression of B-class floral patterning genes.PLoS One 11: e0167614

Mutters RG, Ferreira LGR, Hall AE (1989) Proline content of the anthersand pollen of heat-tolerant and heat-sensitive cowpea subjected to dif-ferent temperatures. Crop Sci 29: 1497–1500

Ohama N, Sato H, Shinozaki K, Yamaguchi-Shinozaki K (2017) Tran-scriptional regulatory network of plant heat stress response. TrendsPlant Sci 22: 53–65

Oshino T, Abiko M, Saito R, Ichiishi E, Endo M, Kawagishi-Kobayashi M,Higashitani A (2007) Premature progression of anther early develop-mental programs accompanied by comprehensive alterations in tran-scription during high-temperature injury in barley plants. Mol GenetGenomics 278: 31–42

Pachauri RK, Allen MR, Barros VR, Broome J, Cramer W, Christ R,Church JA, Clarke L, Dahe Q, Dasgupta P, et al (2014) Climate Change2014. Synthesis Report. Contribution of Working Groups I, II and III tothe Fifth Assessment Report of the Intergovernmental Panel on ClimateChange. IPCC, Geneva, Switzerland

Pacini E, Guarnieri M, Nepi M (2006) Pollen carbohydrates and watercontent during development, presentation, and dispersal: a short review.Protoplasma 228: 73–77

Parish RW, Li SF (2010) Death of a tapetum: A programme of develop-mental altruism. Plant Sci 178: 73–89

Parish RW, Phan HA, Iacuone S, Li SF (2012) Tapetal development andabiotic stress: a centre of vulnerability. Funct Plant Biol 39: 553–559

Peet MM, Sato S, Gardner RG (1998) Comparing heat stress effects onmale-fertile and male-sterile tomatoes. Plant Cell Environ 21: 225–231

Prasad PVV, Djanaguiraman M (2011) High night temperature decreasesleaf photosynthesis and pollen function in grain sorghum. Funct PlantBiol 38: 993–1003

Pressman E, Harel D, Zamski E, Shaked R, Althan L, Rosenfeld K, FironN (2006) The effect of high temperatures on the expression and activityof sucrose-cleaving enzymes during tomato (Lycopersicon esculentum)anther development. J Hortic Sci Biotechnol 81: 341–348

Pressman E, Peet MM, Pharr DM (2002) The effect of heat stress on tomatopollen characteristics is associated with changes in carbohydrate con-centration in the developing anthers. Ann Bot (Lond) 90: 631–636

Pressman E, Shaked R, Shen S, Altahan L, Firon N (2012) Variations incarbohydrate content and sucrose-metabolizing enzymes in tomato(Solanum lycopersicum L.) stamen parts during pollen maturation. Am JPlant Sci 3: 252–260

Proels RK, Gonzalez MC, Roitsch T (2006) Gibberellin-dependent induc-tion of tomato extracellular invertase Lin7 is required for pollen devel-opment. Funct Plant Biol 33: 547–554

Ruan YL, Jin Y, Yang YJ, Li GJ, Boyer JS (2010) Sugar input, metabolism,and signaling mediated by invertase: roles in development, yield po-tential, and response to drought and heat. Mol Plant 3: 942–955

Ruberti C, Brandizzi F (2014) Conserved and plant-unique strategies forovercoming endoplasmic reticulum stress. Front Plant Sci 5: 69

Saini HS, Sedgley M, Aspinall D (1984) Developmental anatomy in wheatof male sterility induced by heat stress, water deficit or abscisic acid.Aust J Plant Physiol 11: 243–253

Sakata T, Oshino T, Miura S, Tomabechi M, Tsunaga Y, Higashitani N,Miyazawa Y, Takahashi H, Watanabe M, Higashitani A (2010) Auxinsreverse plant male sterility caused by high temperatures. Proc Natl AcadSci USA 107: 8569–8574

Sato S, Kamiyama M, Iwata T, Makita N, Furukawa H, Ikeda H (2006)Moderate increase of mean daily temperature adversely affects fruit set

of Lycopersicon esculentum by disrupting specific physiological processesin male reproductive development. Ann Bot (Lond) 97: 731–738

Scharf KD, Berberich T, Ebersberger I, Nover L (2012) The plant heatstress transcription factor (Hsf) family: structure, function and evolu-tion. Biochim Biophys Acta 1819: 104–119

Schoper JB, Lambert RJ, Vasilas BL, Westgate ME (1987) Plant factorscontrolling seed set in maize : the influence of silk, pollen, and ear-leafwater status and tassel heat treatment at pollination. Plant Physiol 83:121–125

Selinski J, Scheibe R (2014) Pollen tube growth: where does the energycome from? Plant Signal Behav 9: e977200

Sharkey TD (2005) Effects of moderate heat stress on photosynthesis: im-portance of thylakoid reactions, rubisco deactivation, reactive oxygenspecies, and thermotolerance provided by isoprene. Plant Cell Environ28: 269–277

Sharma KD, Nayyar H (2016) Regulatory networks in pollen developmentunder cold stress. Front Plant Sci 7: 402

Sheoran IS, Sproule KA, Olson DJH, Ross ARS, Sawhney VK (2006)Proteome profile and functional classification of proteins in Arabidopsisthaliana (Landsberg erecta) mature pollen. Sex Plant Reprod 19: 185–196

Singh A, Grover A (2008) Genetic engineering for heat tolerance in plants.Physiol Mol Biol Plants 14: 155–166

Srivastava R, Deng Y, Shah S, Rao AG, Howell SH (2013) BINDINGPROTEIN is a master regulator of the endoplasmic reticulum stresssensor/transducer bZIP28 in Arabidopsis. Plant Cell 25: 1416–1429

Suzuki K, Takeda H, Tsukaguchi T, Egawa Y (2001) Ultrastructural studyon degeneration of tapetum in anther of snap bean (Phaseolus vulgaris L.)under heat stress. Sex Plant Reprod 13: 293–299

Tang RS, Zheng JC, Jin ZQ, Zhang D, Huang H, Chen LG (2008) Possiblecorrelation between high temperature-induced floret sterility and en-dogenous levels of IAA, GAs and ABA in rice (Oryza sativa L.). PlantGrowth Regul 54: 37–43

Tunc-Ozdemir M, Tang C, Ishka MR, Brown E, Groves NR, Myers CT,Rato C, Poulsen LR, McDowell S, Miller G, Mittler R, Harper JF (2013)A cyclic nucleotide-gated channel (CNGC16) in pollen is critical forstress tolerance in pollen reproductive development. Plant Physiol 161:1010–1020

Vierling E (1991) The roles of heat-shock proteins in plants. Annu Rev PlantPhysiol Plant Mol Biol 42: 579–620

Volkov RA, Panchuk II, Mullineaux PM, Schöffl F (2006) Heat stress-induced H2O2 is required for effective expression of heat shock genesin Arabidopsis. Plant Mol Biol 61: 733–746

Wang L, Ruan YL (2016) Critical roles of vacuolar invertase in floral organdevelopment and male and female fertilities are revealed throughcharacterization of GhVIN1-RNAi cotton plants. Plant Physiol 171: 405–423

Xie HT, Wan ZY, Li S, Zhang Y (2014) Spatiotemporal production of re-active oxygen species by NADPH oxidase is critical for tapetal pro-grammed cell death and pollen development in Arabidopsis. Plant Cell26: 2007–2023

Yi J, Moon S, Lee YS, Zhu L, Liang W, Zhang D, Jung KH, An G (2016)Defective Tapetum Cell Death 1 (DTC1) regulates ROS levels by bindingto metallothionein during tapetum degeneration. Plant Physiol 170:1611–1623

Zanor MI, Osorio S, Nunes-Nesi A, Carrari F, Lohse M, Usadel B, KühnC, Bleiss W, Giavalisco P, Willmitzer L, et al (2009) RNA interference ofLIN5 in tomato confirms its role in controlling Brix content, uncovers theinfluence of sugars on the levels of fruit hormones, and demonstratesthe importance of sucrose cleavage for normal fruit development andfertility. Plant Physiol 150: 1204–1218

Zhang X, Li J, Liu A, Zou J, Zhou X, Xiang J, Rerksiri W, Peng Y, Xiong X,Chen X (2012) Expression profile in rice panicle: insights into heat re-sponse mechanism at reproductive stage. PLoS One 7: e49652

Zhang XW, Xiong HR, Liu AL, Zhou XY, Peng Y, Li ZX, Luo GY, Tian XR,Chen XB (2014) Microarray data uncover the genome-wide gene ex-pression patterns in response to heat stress in rice post-meiosis panicle. JPlant Biol 57: 327–336

1976 Plant Physiol. Vol. 173, 2017

Rieu et al.

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