Global analysis of Two Component System (TCS) member of chickpea and other legume genomes implicates its role in enhanced nodulation

Nodule organogenesis is governed primarily by phytohormone cytokinin. We observed the significant nodulation in chickpea at particular cytokinin concentration (2.5x10-7) which indicated the importance of cytokinin in nodule development. Cytokinin signaling is mediated through the Two Component System (TCS) which comprises of sensor histidine kinases (HKs), histidine phosphotransfer proteins (HPs), and response regulators (RRs). Therefore, we analyzed the interconnection of cytokinin with TCS molecules during root nodule development through global analysis of TCS candidates in legumes with special consideration to cytokinin receptor and Type-B RR member. We have conducted an in depth global analysis of TCS family members in chickpea and other legumes, Medicago and pigeon pea. Higher number of TCS genes were found in Medicago (96), followed by pigeonpea (75) and chickpea (67). A good correlation between TCS members with their corresponding total number of genes were observed in all three-legume species. Collinearity analysis of TCS revealed phylogenetically closer proximity of Cicer to Medicago followed by Glycine than Cajanus. Comprehensive analysis of 3-dimensional structure, genomic organisation and domain arrangement showed a conservation of TCS members within species. In depth investigation showed that HKs were mainly conserved among TCS members in legumes and non-legumes while divergence occurred at level of RRs. Further, Type-B RRs were functionally most diversified in RRs based on phylogeny, syntenic and transcript analysis. Few numbers of segmentally duplicated pair of TCS showed difference in their transcriptional regulation suggesting the functional evolution. For functional characterization the cre1 mutants of (Medicago) were complemented with chickpea cytokinin responsive HKs and nodulation deficient phenotype of mutants were restored. A synchronous cytokinin-induced expression of chickpea cytokinin receptor HKs and CaNIN provides strong relation of cytokinin signaling during nodulation. Furthermore, interesting potential candidate CaRR13 was selected to deduce the underlying molecular mechanism of nodulation, chickpea in specific and legumes in general.