The of energy i.e. biodiesel from non-edible crops which

The rising demand for fuels has raised an interest towards
selecting an alternate and promising renewable source of energy i.e. biodiesel
from non-edible crops which do not compete with food crops and agricultural
lands. Jatropha (Jatropha curcas L.),
a non-edible energy crop of the family euphorbiaceae, has the potential of
providing biodiesel feedstock due to high seed oil content (42%). The stumbling roadblock for commercialization of Jatropha-based
biodiesel is low seed yield per inflorescence. Low female to male
flower ratio (1:25-30)
is considered as a major limiting factor responsible for
low seed yield in Jatropha. The molecular basis female flower and the transition into
female flower as well as the genetic factors contribute to differential female
to male flower ratio in different genotypes has not been known in J. curcas. To increase the seed yield, an exogenous cytokinin application was
performed on floral meristems which resulted in an increase of total flower
count with a higher female to male flower ratio but the seed biomass did not
increase in the same proportion. Molecular mechanisms underlying carbon capture
and flux affected between the source and sink (flowers/fruits/seed) due to
cytokinin application have not been studied yet. Thus, the current study, therefore,
investigated: (1) the molecular cues for floral transitions and female
flowering in high female flower genotype of Jatropha
curcas and then validating the expression status identified genes in low (1:25-30)
female to male flower ratio genotype; (3) deciphering molecular components of cytokinin on flowering and source-sink relationship of Jatropha curcas L.

The expression profile of 42 genes for floral organ
development and sex determination was done at six floral developmental stages
of a J. curcas genotype was
investigated. Key genes identified for reproductive phase
transition were CUC2, CRY2, PIN1, TFL1, AP1, SUP, CKX1 and TAA1. Further, CUC2, TAA1, CKX1 and PIN1 were identified
for their role in female flowering and SUP
and CRY2 for female flower
transition. Relative expression of these
genes with respect to low female flower ratio genotype showed significant increase
in expression of TAA1, SUP, CKX1 and CRY2 genes at a stage, where transition towards female flower occurs, thereby
suggesting that these genes possibly play a significant role in female
flowering by promoting abortion of male flower primordia. To understand the transcriptional
regulation of these developmental transitions, promoter regions of key genes were
analyzed for regulatory elements. GAREAT, UP2ATMSD and MYB1AT were identified uniquely
for genes associated with female flowering.  Furthermore, to understand,
the molecular mechanisms underlying carbon capture
and flux affected between the source and sink in developing flowers, fruits and
seeds after cytokinin application, RNA-seq based comprehensive transcriptome sequencing of inflorescence meristems (treated with cytokinin) and control (untreated
inflorescence meristems) at time-intervals of 15 & 30 days, respectively of
J. curcas by using NextSeq 500 platform of Illumina was
performed. 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 15 days of cytokinin treatment however, they
were downregulated after 30 days. Five 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

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The current study provides repertoire of key genes which
can be potential targets to increase the feedstock yield of Jatropha through transgenic
or molecular breeding approaches. Further this study provides information on
molecular mechanisms of female flower development and transitions towards
female flowers. The study also shed light on the metabolic pathways affected by
cytokinin treatment thereby altering source to sink ratio, in turn the feedstock
yield of Jatropha. By understanding this phenomenon suitable gene target were identified
for increasing the yield through genetic interventions.