Comparative transcriptomics reveals a reduction in carbon capture and flux between source and sink in cytokinin-treated inflorescences of Jatropha curcas L.

Abstract

The low seed yield of Jatropha curcas has been a stumbling block in realizing its full potential as an ideal bioenergy crop. Low female to male flower ratio is considered as a major limiting factor responsible for low seed yield in Jatropha. An exogenous cytokinin application was performed on floral meristems to increase the seed yield. This resulted in an increase of total flowers count with a higher female to male flower ratio. However, the seed biomass did not increase in the same proportion. The possible reason for this was hypothesized to be the lack of increased photosynthesis efficiency at source tissues which could fulfil the increased demand of photosynthates and primary metabolites in maturing seeds. After cytokinin application, possible molecular mechanisms underlying carbon capture and flux affected between the source and sink in developing flowers, fruits and seeds were investigated. Comparative transcriptome analysis was performed on inflorescence meristems (treated with cytokinin) and control (untreated inflorescence meristems) at time intervals of 15 and 30days, respectively. KEGG-based functional annotation identified various metabolic pathways associated with carbon capture and flux. Pathways such as photosynthesis, carbon fixation, carbohydrate metabolism and nitrogen metabolism were upregulated after 15days of cytokinin treatment; however, those were downregulated after 30days. Five genes FBP, SBP, GS, GDH and AGPase showed significant increase in transcript abundance after 15days of treatment but showed a significant decrease after 30days. These genes, after functional validation, can be suitable targets in designing a suitable genetic intervention strategy to increase overall seed yield in Jatropha.