Understand ratio genotypes and key genes associated with female


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,
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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Comparative transcriptome-based analysis of inflorescences
treated with cytokinin and untreated inflorescences provided details on
molecular components associated with compromised yield in Jatropha. The current
study revealed that the carbon fixation and its allocation was affected by BA
application. GO and KEGG based functional annotation showed that processes like
carbohydrate metabolism and nitrogen metabolism were
upregulated after 15 days of cytokinin treatment however, they were
downregulated after 30 days. Key genes FBP, SBP, GS,
GDH and AGPase were identified to be significantly downregulated
after 30 days of cytokinin application and are associated with biomass and
yield. These results would be critical for understanding the molecular dynamic
of souce-sink interaction in response to cytokinin application in Jatropha.

Transcriptome sequences and data generated was
submitted on a public domain (Link: