QTL mapping and gene mining to identify genes on soybean (Glycine max) associated with NopB of Sinorhizobium fredii HH103

Soybean is a special crop that can utilize N-2 in the air via symbioses with Rhizobium spp. The formation of effective nodules is a complex process in which nodulation outer proteins (Nops) are determinants of establishment of a symbiotic relationship. We constructed a Sinorhizobium fredii HH103 omega nopB mutant. A nodulation test showed that the mutant had a negative effect on the Suinong14, ZYD00006, Dongnong594 and Charleston soybean lines. Recombinant inbred soybean lines were independently inoculated with the mutant and wild-type strains, and five and four quantitative trait loci (QTLs) were identified by analysing the nodule number (NN) and nodule dry weight (NDW), respectively. We chose one QTL that overlapped with other studies and a novel QTL identified in our study and selected six candidate genes for further analysis. The qRT-PCR analysis showed that only changes in Glyma.17G166200 expression depended on NopB. Further analysis showed that Glyma.17G166200 encoded a protein with a D-glucose-binding domain and a serine-threonine/tyrosine protein kinase catalytic domain that was involved in the abscisic acid (ABA) pathway.