Shantanu DasPhD Scholar

Dept. of Plant Breeding and GeneticsAssam Agricultural University, Jorhat-785013

NUE

ContentsIntroduction.

Need for improvement of NUE

Understanding plant response to N limitation

Physiological basis of NUE

Molecular basis of NUE

Approaches for improving NUE

Case study

Ideotype of Nitrogen use efficient genotype

The relationship between NUE and grain yield

Conclusion

What is NUE ?(Yield obtained per unit of available nitrogen (N) in the soil)

Physiological NUE =Eefficiency with which the plant

uses N from acquired available N to total plant dry matter

N imported from the field to the crop product Agronomic NUE = N applied.

NUE is the product of uptake efficiency and utilization efficiency.

NUE in plants is a complex phenomenon that depends on

a number of internal and external factors.

Where, When and Why NUE traits are required?

It’s required in all environmental condition where yield is required, because NUE crop yield. ⍺

For abiotic stress improvement in crops, NUE has become the

second priority after drought both in the private and in the public sector.

To minimize N loss, maximize N uptake & reduce environmental pollution.

It’s required in all environmental condition where yield is required, because NUE crop yield. ⍺

For abiotic stress improvement in crops, NUE has become the

second priority after drought both in the private and in the public sector.

To minimize N loss, maximize N uptake & reduce environmental pollution.

Soil Available N

Key events responsible forKey events responsible for soil available N soil available N

Global Status of N fertilizer consumption & NUE

Global Status of N fertilizer consumption & NUE

There is 20-fold increase in the global use of N fertilizer applications during the past five decades (Glass, 2003) and this is expected to increase at least threefold by 2050 (Good et al., 2004).

The current average NUE in the field is approximately 33% and substantial proportion of the remaining 67% is lost into the environment, especially in the intensively cropped area.

It is estimated that 1% increase in NUE could save $1.1 billion annually.

Need for improvement of NUE

Nitrogen (N) must be supplemented to meet the food production demands of an ever-increasing population.

The cost of mineral nitrogen fertilizer accounts for a major portion of the total cost of production.

N recovery by crops is only 30% to 35% of that applied and remaining 65% to 70% is lost into the environment through a combination of ammonia volatilization, denitrification, leaching, immobilization and runoff.

Therefore, Physiologist and plant breeders need to develop cultivars that can exploit N more efficiently in order to minimize loss of N, reduce environmental pollution, decrease input cost and make more economic use of the absorbed N.

Understanding plant response to N limitation

• There may be two type of response to N limitation (i.e.)

1. Adaptive response and

2. Non-adoptive response

Adaptive responses Increase in N uptake. Retardation of growth and photosynthesis. Remobilization of N from older to young leaves and reproductive parts. Increased anthocyanin accumulation.

Non -adaptive responses Fail to accumulate anthocyanin. Having sudden senescence. Unable to remobilize N metabolites from rosette leaves towards

developing seeds.

Physiological components of NUE

There may be a two components of NUE

1. Nitrogen Uptake Efficiency

2. Nitrogen Utilization Efficiency

1. Nitrogen uptake efficiency(Amount of absorbed N/quantity of available N)

N uptake efficiency drives biomass production and depend on

Amount of N uptake

Storage

Assimilation

N uptake (Kant & Rothstein., 2010)

For plant N is mainly available in the form of NO3- and NH4

+

There are 3 type of NO3- transporter - LATS, cHATS & iHATS

Km value of cHATS-(about 6-20 μM) [Forde and Clarkson, 1999]

Km value of iHATS-(about 13-79 μM) [Forde and Clarkson, 1999]

Several structural gene involve in N uptake

NRT1 families member (NRT1.1 and NRT1.2) are characterized as LAT

NRT2 families member (NRT2.1 and NRT2.2) are characterized as HAT

AMT families member are involved in NH4+ (AMT1, AMT2 & AMT3)

N Assimilation

NO3- after entering into the plant cell, assimilation is begin .

N Storage

Absorbed N may stored in the vacoule or directly assimilate into amino acid

Nitrate reductase No3

- NO2-

Nitrate assimilation

Cytoplasm

NO2- Nitrite reductase NH4

+Move NO2-

Nitrate reductase encoded in nucleus and synthesized in cytoplasm.

Ammonium assimilation

2. Nitrogen Utilization Efficiency (Efficiency of a plant to utilized N from acquired available N

in the plant for production of biomass)

Utilization efficiency involved N remobilization.

At the reproductive stage both N assimilation & N remobalization become critical.

Leaves & shoot act as a source for amino acid to the reproductive and storage organ.

Upto 80% of the grain N content is derived from leaves in rice and wheat.

During leaf senescence N release via protease activities.

Amino acid

The predominant gene families which involved in phloem loading process is AAP (AAP1 - AAP8)

Loading into

Phloem

NH4+Stored Protein

Molecular basis of NUE

Genetics of NUE

NUE is a complex quantitative traits which involves many genes.

Expression of multiple gene depend on a number of internal and external factors.

There are 100s of nitrate responsive gene.

For their transcription require regulatory sequence i.e. NRE (Nitrate responsive element).

One of the such sequence originally reported to be comprised of an A[G/C]TCA sequence.

These sequence is randomly distributed throughout the

genome.

QTL mapping is a powerful tool for analysis of complex NUE.

By using QTL mapping in some model spp. such as rice, arabidopsis and maize, candidate genes encoding enzyme that involved in N uptake, assimilation and utilization have been identified.

Contd. (genetics of NUE)

Gene involved in Nitrogen uptake (Kant et al., 2011)

Gene involved in Nitrate Assimilation (Good et. al., 2004)

Contd.

Agronomic Approach

Optimum N Application_________________

According to phonological stages,

Based on the crop N demand,

Knowledge of plant N uptake efficiency,

Based on soil N status or

Using controlled-release fertilizers - Nitroform® - Nutralene® - IB Nitrogen

NUE is affected by

N uptake efficiency - Root characteristics

Physiological N use efficiency (PE)

-mode of photosynthesis i.e. C3 or C4

- N supply

N partitioning b/w leaf & stem

Efficiency of N use in CO2 fixation

Increasing leaf N content

Delay leaf senescence

Higher canopy structure

Physiological Approach

Conventional approach

Selection

Backcross method

Molecular approach

Marker assisted selection

Genetic Approach

F2

P2

F1

P1 xResistantSusceptible

Marker assisted backcrossing Marker assisted backcrossing

Marker-assisted backcrossing (MAB)

There are three levels of selection in which markers may be applied in backcross breeding.

Foreground selection : to screen for the target trait. Recombinant selection: to minimize linkage drag. Background selection: to the recovery of the recurrent

parent genome.

Transgenic approach (Abrol, Raghuram & Sachdev, 2007)

GENE GENE SOURCE TARGET PLANTPHENOTYPE OBSERVED

Nrt 2.1Nicotiana

plumbaginifoliaN. tabaccum

Increased nitrate influx under low N conditions

NR N. plumbaginifolia N. tabaccumHigher

Nitrate assimilation

NiR Spinacea oleracea ArabidopsisHigher

Ammonium accumulation

GS1 Glycine max Lotus corniculatus Accelerated senescence

CASE STUDY

Zhang et al., 2015Zhang et al., 2015

Identified a major QTL (TOND1) on the long arm of chromosome 12, confer tolerance to nitrogen deficiency in Teqing

YIL 105 x Teqing

F1

311 F2

34 75

41

Contain TOND 1 Don’t Contain TOND1

150 cultivars (75 Indica and 75 Japonica cultivars) and regions

Whether rice cultivars having the TOND 1 allele exhibit strong tolerance to N deficiency ?

Over-expression of TOND1 increased the tolerance to N deficiency in the TOND1- deficient rice cultivars.

Identification of TOND 1 provides a molecular basis of breeding

for breeding rice varieties with improved grain yield despite input

of N fertilizer

Concluded

Ideotype of Nitrogen use efficient genotype

Increased amount and activity of NR & NiR

Increased amount and activity of GS & GOGAT

High root to shoot ratio

High root vigor & root hair

High root length density

N-induced root proliferation Microbial symbiosis

Grain yield is positively correlated with N uptake efficiency and N utilization efficiency

Grain yield is positively correlated with N uptake efficiency and N utilization efficiency

There is a considerable genetic variability for NUE which provide opportunity for genetic improvement.

Several candidate gene responsible for NUE have been identify in several crops like Arabidopsis, Rice and maize etc.

By hybridization programme, its is enable to transfer identified NUE related QTL to the genotype having good agronomic background.

Incorporation of NUE trait in a genotype will increase the ultimate grain yield which will contribute to our national economy.

NUE