-Methylated Isoflavones Induce Genes of and Pratensein Promotes Nodulation in Chickpea.

Legume plants form symbiotic relationships with rhizobia, which allow plants to utilize atmospheric nitrogen as a nutrient. This symbiosis is initiated by secretion of specific signaling metabolites from the roots, which induce the expression of genes in rhizobia. These metabolites are called gene inducers (NGIs), and various flavonoids have been found to act as NGIs. However, NGIs of chickpea, the second major pulse crop, remain elusive. We conducted untargeted metabolome analysis of chickpea root exudates to explore metabolites with increased secretion under nitrogen deficiency. Principal component (PC) analysis showed a clear difference between nitrogen deficiency and control, with PC1 alone accounting for 37.5% of the variance. The intensity of two features with the highest PC1 loading values significantly increased under nitrogen deficiency; two prominent peaks were identified as -methylated isoflavones, pratensein and biochanin A. RNA-seq analysis showed that they induce gene expression in the symbiont, suggesting that pratensein and biochanin A are chickpea NGIs. Pratensein applied concurrently with at sowing promoted chickpea nodulation. These results demonstrate that pratensein and biochanin A are chickpea NGIs, and pratensein can be useful for increasing nodulation efficiency in chickpea production.