QTL analysis of nodule traits and the identification of loci interacting with the type III secretion system in soybean.

ABSTRACT

Symbiotic nitrogen fixation is the main source of nitrogen for soybean growth. Since the genotypes of rhizobia and soybean germplasms vary, the nitrogen-fixing ability of soybean after inoculation also varies. A few studies have reported that quantitative trait loci (QTLs) control biological nitrogen fixation traits, even soybean which is an important crop. The present study reported that the Sinorhizobium fredii HH103 gene rhcJ belongs to the tts (type III secretion) cluster and that the mutant HH103ΩrhcJ can clearly decrease the number of nodules in American soybeans. However, few QTLs of nodule traits have been identified. This study used a soybean (Glycine max (L.) Merr.) 'Charleston' × 'Dongnong 594' (C × D, n = 150) recombinant inbred line (RIL). Nodule traits were analysed in the RIL population after inoculation with S. fredii HH103 and the mutant HH103ΩrhcJ. Plants were grown in a greenhouse with a 16-h light cycle at 26 °C and an 8-h dark cycle at 18 °C. Then, 4 weeks after inoculation, plants were harvested for evaluation of nodule traits. Through QTL mapping, 16 QTLs were detected on 8 chromosomes. Quantitative PCR (qRT-PCR) and RNA-seq analysis determined that the genes Glyma.04g060600, Glyma.18g159800 and Glyma.13g252600 might interact with rhcJ.