Heritability, signal perception and autoregulation of root nodulation in chickpea

Chickpea (Cicer arietinum L.) establishes symbiotic interactions with Mesorhizobium to develop root nodules where nitrogen fixation occurs. This symbiotic relationship can fix atmospheric nitrogen (N2) up to 140 kg N/ha that contribute nearly 80% nitrogen requirement of the crop. Global researchers had revealed the existence of natural variations in chickpea germplasm for nodulation traits with high heritability. Surprisingly, the contribution of environmental variation is too low for Biological Nitrogen Fixation (BNF) traits and high broad-sense heritability (>60) was observed for early nodulation, late nodule senescence and high nodule number traits. Correlation studies indicated a strong positive correlation between nodule number at flowering stage with total nodule weight and plant biomass and seed protein content. Nod Factor receptors in chickpea (CaNFR1 and CaNFR5) are characterized recently that forms phylogenetically distinct group along with M. truncatula, P. sativum, and L. japonicus. Critical role of cytokinin signalling through members of two component system (TCS) in nodulation was investigated in chickpea. The chickpea ortholog CaHK19 was the master spigot of cytokinin perception in chickpea. The co-expression pattern of CaHKs and CaNIN clearly indicated a link between cytokinin perception and downstream expression of CaNIN in chickpea as earlier established in Medicago. Genes involved in AON pathway are partially revealed in chickpea. CaRND1, CaRDN2, and CaRDN3 (C. arietinum Root-Determined Nodulation) function as receptors for signals produced from the roots. Revealing the molecular basis of root nodule organogenesis and their regulatory mechanisms along with identification of potential genetic stock will help on breeding or engineering chickpea genotypes with high symbiotic efficiency, extended nitrogen fixation and high symbiotic efficiency make grain legumes as nitrogen fixing factories to fertilize the soil in a sustainable way.