Understand the molecular mechanisms of floral development, sexdetermination and floral transitions (vegetative to reproductive,differentiation of floral buds into male/female and transition towards femaleflowering) and the alteration in source to sink interaction after cytokininsapplication are important for instigating the genetic intervention strategy toincrease feedstock yield of Jatropha.
Current study provides the geneticdifferences contributing towards female flowering between high vs low ratiogenotypes and key genes associated with female flower development. Also throughcomparative transcriptomics, molecular mechanisms unveiled the cause ofcompromised yield in response to cytokinin application. Through comparative genomics, floral genes wereidentified and their relative expression status was studies at different floraldevelopmental stages. Gene identified for vegetative to reproductive phasetransition in Jatropha were SUP, TFL1,AP1 CUC2, CRY2, PIN1 and TAA1 and showed a relative increase inexpression 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 ~1953folds 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. Fromthese, SUP and CRY2 genes showed ~59 folds increase in expression level inintermediates followed by ~18 folds in female floral buds.
They were found to be associated withtransition towards female flowering by suppressing the stamen development,allowing females to develop. TAA1, CUC2, PIN1, FT, CKX1 showed higher expression in femaleflowers whereas TFL1, AP1 and TypA1 were expressed higher in male floral buds. Further on comparingexpression in male, female and intermediates between high and low female tomale flower ratio genotypes, it was observed that SUP gene was upregulated in intermediate stage with ~7 folds whencompared with low ratio genotype.
CUC2gene in female floral buds expressed ~10 folds higher in high female flowerratio genotype. These results showed that the female development was strong inhigh ratio genotype along with increase abortion rate of stamens. By correlatingthe expression of these genes possible interactions between them and thepathways might be contributing in development of females and their transition werealso predicted. PCA analysis proved useful in correlating the data ofexpression analysis with male and female florals buds.
The current studyprovided a repertoire of key genes for female flowering which can be furtherconsidered as suitable candidates enhancing seed yield by increasing number offemale flowers. In-silico analysis ofpromoter regions of key genes revealed the presence of putative regulatoryelements associated with floral transition and associated pathways were ARR1AT, BIHD1OS, MYB1AT, POLLEN1LELAT52, and WRKY71OS. They were found to beassociated with gibberellins, cytokinins, abscisic acid, andauxin pathways as well as pollen development. GARE2OSREP1 and CARGATCONSENSUS were unique elementsfound to be associated with genes involved in female flowering. Overall, thesefindings together with the previous information provided a more comprehensiveunderstanding mechanism of sex determination in J. curcas. Comparative transcriptome-based analysis of inflorescencestreated with cytokinin and untreated inflorescences provided details onmolecular components associated with compromised yield in Jatropha.
The currentstudy revealed that the carbon fixation and its allocation was affected by BAapplication. GO and KEGG based functional annotation showed that processes likecarbohydrate metabolism and nitrogen metabolism wereupregulated after 15 days of cytokinin treatment however, they weredownregulated after 30 days. Key genes FBP, SBP, GS,GDH and AGPase were identified to be significantly downregulatedafter 30 days of cytokinin application and are associated with biomass andyield. These results would be critical for understanding the molecular dynamicof souce-sink interaction in response to cytokinin application in Jatropha.Transcriptome sequences and data generated wassubmitted on a public domain (Link: http://14.
139.240.55/NGS/download.php).
