Regulation of nodule number by GmNORK is dependent on expression of GmNIC in soybean

Abstract

Root nodules are highly organized root organs where nitrogen fixation takes place in, and its formation are the results of complicated interactions between legumes and rhizobia. Nodule number is tightly controlled by Legumes to ensure optimal growth without energy loses wasted by excessive number of nodules. One of major factors controlling of nodule number is nitrate availability in the soil. However, during symbiotic development, the details of Nod factor signaling associated with nitrate regulation of nodulation are unknown. NORK, the immediately downstream component of these Nod factor receptors is central to the Nod factor signaling. NIC1, a CLE peptide-encoding gene in soybean (Glycine max), play an important role in nitrate regulation of nodulation. In this study, specified RNAi construct of GmNORK was generated and transformed into soybean roots by agrobacterium rhizogenes-mediated hairy root transformation. We found that the nodule number decreased substantially in GmNORK knock-down soybean transgenic roots. The expression levels of GmNIC1 in the GmNORK RNAi soybean transgenic roots is substantially reduced after rhizobial inoculation compared with the control soybean transgenic roots. Our data suggest that nitrate regulation of nodulation was affected by Nod factor signaling during nodule development in soybean, providing valuable information toward understanding the functions of GmNORK and GmNIC1 in symbiotic signaling and nodule development.