Soybean gene expression correlated with symbiotic rhizobial nitrogen fixation activity

Soybean ( Glycine max L.) can establish a symbiotic relationship with rhizobia. However, little is known about the host plant genes that correlate with the nitrogen fixation activity of symbiotic rhizobia. In this study, we investigated soybean genes that correlate with bacterial symbiotic nitrogen fixation in two experiments. In the first experiment, soybean seeds were inoculated with two strains of soybean rhizobia exhibiting different nitrogen fixation activities and were grown in the field until the R1 stage. Subsequently, the roots and nodules were subjected to RNA-seq analysis to identify the expression of soybean genes related to bacterial nitrogen fixation. In the second experiment, to confirm host gene expressions dependent on bacterial nitrogen fixation activity, nod+/fix-(Delta nif gene) mutants and the wild type were inoculated into soybean, and gene expressions were evaluated by qRT-PCR. GmNRT2.5, a high-affinity nitrate transporter gene, was correlated with nitrogen fixation activity. qPCR analysis of roots and nodules inoculated with a nod+/fix-mutant revealed that GmNRT2.5 on chromosome 8 (Glyma.08G284000: GmNRT2.5 Chr8) was particularly correlated with nitrogen fixation activity in the root nodule section. Based on the results, it is suggested that GmNRT2.5 Chr8 may function as a regulatory gene bridging nitrogen fixation and nitrate absorption from the soil. Therefore, GmNRT2.5 Chr8 might be a useful host gene for estimating symbiotic nitrogen fixation activity.