Understand the molecular mechanisms of floral
development, sex determination and floral transitions (vegetative to
reproductive, differentiation of floral buds into male/female and transition
towards female flowering) and the alteration in source to sink interaction
after cytokinins application are important for instigating the genetic intervention strategy to increase
feedstock yield of Jatropha. Current study provides the genetic
differences contributing towards female flowering between high vs low ratio
genotypes and key genes associated with female flower development. Also through
comparative transcriptomics, molecular mechanisms unveiled the cause of
compromised yield in response to cytokinin application. 

Through comparative genomics,
floral genes were identified and their relative expression status was studies
at different floral developmental stages. Gene identified for vegetative to
reproductive phase transition in Jatropha were SUP, TFL1, AP1 CUC2, CRY2, PIN1 and TAA1 and showed a
relative increase in expression of ~426 folds. For development of floral organ
genes AP1, CUC2, RGL, EIN2, IPT2, TypA1, PIN1 were identified from which PIN1, AP1 and TypA1 showed a
significant increase in expression of about ~1953 folds and others showed ~13
folds increase in expression at initial floral buds. Gene for sex determination
like CRY2, TAA1, CUC2, PIN1, FT, CKX1, SUP, TFL1,
AP1 and TypA1 were identified in Jatropha. From these, SUP and CRY2 genes showed
~59 folds increase in expression level in intermediates followed by ~18 folds
in female floral buds.  They were found
to be associated with transition towards female flowering by suppressing the
stamen development, allowing females to develop. TAA1, CUC2, PIN1, FT, CKX1 showed higher
expression in female flowers whereas TFL1,
AP1 and TypA1 were expressed higher in male floral buds. Further on
comparing expression in male, female and intermediates between high and low female
to male flower ratio genotypes, it was observed that SUP gene was upregulated in
intermediate stage with ~7 folds when compared with low ratio genotype. CUC2 gene in female floral buds expressed
~10 folds higher in high female flower ratio genotype. These results showed
that the female development was strong in high ratio genotype along with increase
abortion rate of stamens. By correlating the expression of these genes possible
interactions between them and the pathways might be contributing in development
of females and their transition were also predicted. PCA analysis proved
useful in correlating the data of expression analysis with male and female
florals buds. The current study provided a repertoire of key genes for female
flowering which can be further considered as suitable candidates enhancing seed
yield by increasing number of female flowers. In-silico analysis of promoter regions of key genes revealed the
presence of putative regulatory elements associated with floral transition and
associated pathways were ARR1AT, BIHD1OS, MYB1AT,
POLLEN1LELAT52, and WRKY71OS. They were found to be associated with gibberellins, cytokinins, abscisic acid, and auxin pathways as well as
pollen development. GARE2OSREP1 and CARGATCONSENSUS were unique elements found to be
associated with genes involved in female flowering. Overall, these
findings together with the previous information provided a more comprehensive
understanding mechanism of sex determination in J. curcas. 

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