In plants, sex determination is the process
through which unisexual flowers are formed. There are two dominant ways of
unisexual flower development: One is the emergence of only one type of sex
organ without formation of any bisexual tissue at any stage floral development.
Whereas in other; there is initiation of a bisexual floral meristem with both
stamens and pistils followed by a developmental arrest or abortion of one sex
with only the stamens or the carpels attaining functional maturity. The step
impeding the development of floral sex organs is at an immature stage well
prior to reaching sexual maturity (reviewed by Kinney, Columbus, & Friar,
2008). Many monoecious species progresses through an early hermaphroditic stage
to differentiated (unisexual) stages later in floral development, by aborting
or arresting either of the sexual organs (Ainsworth, 2000). Jatropha being a monoecious
plant, sexual differentiation occurs by abortion of stamens, allowing the
female flowers to develop. No female tissues were found in fully developed male
flowers however remains of male tissues (aborted stamens) were found in a fully
developed female flowers. Transcriptome analysis of Jatropha floral buds
identifies Tasselseed 2 (TS2), a sex
determination gene which is required for stamen development and its reduced
expression promotes the carpel development by aborting male tissues. Recently,
transcriptome analysis of male and female floral buds at different
developmental stages of Jatropha identifies CRABS CLAW gene for sex
differentiation. They have also identified an ATP-binding protein promotes
stamen degeneration in female flower at later stage of development. Chlorophyll A/B-binding protein, ubiquitin
carboxyl-terminal hydrolase and inorganic phosphate transporter contribute to
the female organ development whereas cytochrome C oxidase subunit 1 contributes
to the development of the stamen. Gibberellin-regulated protein 4-like protein
and AMP-activated protein kinase  genes were
found to be associated with stamen differentiation, whereas auxin response
factor 6-like protein, AGL-20, CLV1, auxin-induced protein 22D, RING-H2 finger
protein ATL3J, and r2r3-myb transcription factor contribute to embryo sac
development in female flowers. COX, ARP1, GID1 and auxin-induced protein X10A
are expressed in both male and female flowers (Xu et al 2016). Functional study of JcFT, a floreign and a key
regulator of flowering pathway showed highest expression level in female
flowers (Li et al 2014).

Transcriptome analysis of other monoecious
plants have been performed to identify genes associated with sex determination.
P450 and ENDO-BETA-1,3-1,4 GLUCANASE
genes were identified for female flowering and CHALCONE SYNTHASE A, DEFECTIVE IN ANTHER DEHISCENCE1 (DAD1) and
found to be associated with pollen development (Rocheta et al 2014). ENDO-BETA-1,3-1,4
GLUCANASE gene possibly inhibits the development of male structure in females
and defect in DAD1 showed defects in anther dehiscence, pollen maturation, and
flower opening (Ishiguro et al., 2001). In Ricinus communis PDC related genes (cysteine protease) identified for
female development and its expression level was increased at the peak of anther
abortion (Lorrain et al., 2003; Wei et al., 2013). 

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In cucumber sex differentiation has been studied extensively and is
genetically controlled by F locus (for females) and M locus (for male). AMINOCYCLOPROPANE-1-CARBOXYLIC
ACID SYNTHASEs (ACS1 & ACS2), ETR2 and ERS genes
associated with ethylene biosynthesis
and signaling pathways were found to be involved in sex determination.  ACS1 & ACS2 promotes gynoecia development by inhibiting male reproductive organs (Saito
et al 2007; Boualem et al., 20089).  ETR2 and ERSI, an ethylene receptors accumulated in
gynoecia, thus promoting female development (Yamasaki et al 2001).  A
MADS-box protein ERAF-17 in cucumber induces female flowering. CTR1-like kinase
protein (CTR1 and CTR2), negative regulators of ethylene 


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