The Soybean Rfg1 Gene Restricts Nodulation by Sinorhizobium fredii USDA193

Abstract

Sinorhizobium fredii is a fast-growing rhizobial species that can establish a nitrogen-fixing symbiosis with a wide range of legume species including soybeans (Glycine max). In soybeans, this interaction shows a high level of specificity such that particular S. fredii strains nodulate only a limited set of plant genotypes. Here we report the identification of a dominant gene in soybeans that restricts nodulation with S. fredii USDA193. Genetic mapping in an F2 population revealed co-segregation of the underlying locus with the previously cloned Rfg1 gene. The Rfg1 allele encodes a member of the Toll-interleukin receptor/nucleotide-binding site/leucine-rich repeat class of plant resistance proteins that restricts nodulation by S. fredii strains USDA257 and USDA205, and an allelic variant of this gene also restricts nodulation by Bradyrhizobium japonicum USDA122. By means of complementation tests and CRISPR/Cas9-mediated gene knockouts, we demonstrate that the Rfg1 allele also is responsible for resistance to nodulation by S. fredii USDA193. Therefore, the Rfg1 allele likely provides broad-spectrum resistance to nodulation by many S. fredii and B. japonicum strains in soybeans.

Celebrating 20 Years of Genetic Discoveries in Legume Nodulation and Symbiotic Nitrogen Fixation

“…Rj2-carrying cultivars of G. max form active N-fixing symbioses with many strains of Bradyrhizobium but not with B. japonicum USDA 122. Rfg1 restricts symbiosis with certain Sinorhizobium fredii strains (Fan et al, 2017). Rj2 and Rfg1 are The entry of rhizobia into the plant cell via tubular ITs triggers a transient ROS burst (1).…”

Improvement of rhizobium‐soybean symbiosis and nitrogen fixation under drought

“…The use of fast-growing rhizobial strains for inoculation has additional advantages with bacterial culture cultivation and risk of contamination reduced due to a shorter generation time (Albareda, Rodríguez-Navarro, & Temprano, 2009). However, fast-growing strains, such as S. fredii USDA 123, exhibit a high level of host specificity due to the presence of the Rfg1 gene and might, therefore, nodulate only a limited number of genotypes (Fan et al, 2017).…”

Genetic and Molecular Mechanisms Underlying Symbiotic Specificity in Legume-Rhizobium Interactions

“…Specificity occurs at both species and genotypic levels ( Broughton et al, 2000 ; Perret et al, 2000 ; Wang et al, 2012 ). This can take place at early stages of the interaction so that the same bacterial strains can infect and nodulate one host plant but not another ( Yang et al, 2010 ; Wang et al, 2012 ; Tang et al, 2016 ; Fan et al, 2017 ). Incompatibility also frequently happens at later stages of nodule development such that nitrogen-fixing efficiency differs significantly between different plant-bacteria combinations ( Wang et al, 2012 , 2017 , 2018 ; Yang et al, 2017 ).…”