SEX DETERMINATION IN PLANTS

Central University of KeralaDept of Genomic Science

Presented by,

DEVARAPALLI PRATAP

Key Words.y Angiosperms y Hermaphrodite y Monoecious y Dioecious y Stamens y Pistil

Sex chromosomes in plantsy Plants producing only female flowers have two X chromosomes that is XX. y Plants producing only male flowers have one X and one Y chromosome that is

XY.y As in humans, the sex chromosomes are cytological distinct.

Sex Determinationy Sex determination is the developmental decision that occurs during the plant life

cycle which leads to the differentiation of two gametes male and female.y The variation in sex expression indicates that there are many sex-determining

mechanisms in plants which are emerged out during the evolution.

Now we will go through different types of sex determination In three types of plantsy Dioecious angiosperm - Silene latifolia y Monoecious angiosperm Zea maize y Homosporous fern - Ceratopteris richardii,

Sex determination in Dioecious angiospermsSilene latifolialatifoliay Early studies on S.latifolia showed that deletions of one arm of the Y chromosome

correlate with hermaphroditism, while deletions of the opposite arm correlate with asexuality.y Y-linked sex-determination by map-based isolation

Techniques done by Donnison et al. isolating male-specific DNA markers using Representational difference analysis (RDA).y These DNA markers attaches on the Y chromosome for the determination of the genes of

malenessy Isolation of genes from the male and female flower buds where the expression of Men-9

gene is observed in male flowers compared to female flowers.

Sex determination in Silene by DNA methylationy Janousek et al. treated seeds with 5-azacytidine, a drug which demethylates DNA when it

has been incorporated into the DNA.y This treatment inhibited the suppression of gynoecium development. y 21% of the treated XY male seeds developed as androhermaphrodite plants and no

gynohermaphroditic plants were observed.y When 5-azacytidine-treated androhermaphroditic flowers were used as female donors of

this trait, none of the progeny seeds developed androhermaphroditic flowers.y 5-azacytidine either induces inhibition of Y-linked female suppressing genes, or activates

autosomal female-promoting genes.

Sex determination in Monoecious angiospermsZea maizemaizey Maize is a Monoecious plant that develops unisexual female and male flowers within

separate inflorescences of the same individual.y The maize inflorescence has the male and female florets initially perfect and become

unisexual by a process of selective arrest.y Abortion of pistils in staminate florets of the tassel, and of stamens in pistillate florets of

the ear takes place.y Gibberellins promote pistil development and suppress stamen development in the ear

florets.

y Another two types of sex determining mutations, Silkless (sk1) and Tassel seed(Ts)have

been identified.y In sk1plants, the pistils and stamens of both ear florets are aborted although secondary

sexual traits remain female, indicating that Sk1 is necessary for the formation of a functional pistil in the upper ear floret [27]. In ts plants, functional pistillate florets form in the tassel.y Non allelic ts mutations :

- ts1and ts2 affect the primary sex characteristics - ts4 and ts6 affect secondary sex characteristicsy The ts2 gene produces hydroxysteroid dehydrogenases which is involved in the pistil

abortion in tassels.y Normally ts2 is epiststic over sk1 in ear, where as sk1 particularly suppresses ts2 in tassel.

Males

Females

Sex determination in Homosporous fernCeratopteris richardiirichardiiy It has the potential to develop either male or hermaphroditic gametophytes. y A Hormone, referred to as ACE - Antheridiogen Ceratopteris produces male

gametophytes.y The epistatic interactions among these genes have been examined and a genetic

regulatory pathway controlling sex determination in Ceratopteris was defined.y Different types of genes participate in this pathway for the determination of sexes.

Transformer gene (TRA) Femaleness Feminization gene (FEM1) Maleness TRA gene Increases MAN1 Decreases FEM1

ACE

ACE signal transduction pathway FEMALENESS Increases HER and FEM1 genes

Decreases TRA

MALENESS

ConclusionBy these we can say that the sex determination in plants was differentiated into different mechanisms regarding to the different species based on the hormones, biochemical agents and some regulatory pathways.

ReferencesCristina.J and Ann.B .,sex determination in plants., Current Opinion in Plant Biology 1998, 1:6872. Stephen.L and Alejandro.C.U., Sex Determination in Flowering Plants., The Plant Cell, Vol. 5, 1241-1251.

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