LAUSR

Background and aimsIn rhizobia, host specificity is controlled by the nodulation outer proteins (Nops). However, the host genes encoding proteins associated with Nops remain unknown.MethodsWe constructed a Sinorhizobium fredii HH103ΩnopL mutant and analyzed the nodule number (NN) and nodule dry weight (NDW) of 10 germplasms inoculated with the mutant or wild-type strain. Using recombinant inbred lines (RILs), the conditional and unconditional quantitative trait loci (QTLs) associated with NopL were detected. The regions overlapping conditional and unconditional QTLs were identified. Additionally, the expression levels of selected candidate genes were analyzed by qRT-PCR.ResultsDepending on the germplasm, NopL positively or negatively affected NN and NDW. The NN and NDW of ‘Charleston’ and ‘Dongnong 594’ (RIL parents) were lower in samples inoculated with Sinorhizobium fredii HH103ΩnopL than in samples inoculated with the wild-type strain. In soybean inoculated independently with Sinorhizobium fredii HH103 and HH103ΩnopL, 11 and 5 unconditional QTLs were identified for NN and NDW, respectively, while five and two conditional QTLs were identified for NN and NDW, respectively. Two overlapping QTLs were identified among the conditional and unconditional QTLs. Furthermore, the enzymes encoded by Glyma.13g170500 and Glyma.07g099700 likely interacted with NopL.ConclusionsThe Glyma.13g170500 and Glyma.07g099700 detected at QTLs represent candidate genes that encode enzymes that interact with NopL to regulate the establishment of symbiotic relationships between rhizobia and soybean.