Allelism of Rps3b and Rps11 revealed by NLR gene capture of resistance genes to Phytophthora sojae in soybean

Exploitation of disease resistance genes in soybean (Glycine max (L.) Merr.), as an effective method for management of Phytophthora sojae (Kauf. & Gerd.), is on the verge of an impasse. Few of the known resistance genes are commercially exploited, and even fewer have been precisely identified. Therefore, little is known about the identities or relationships between those genes, a hindrance preventing optimal introgression of new sources of resistance into elite soybean lines. In this study, we have applied state-of-the-art nucleotide-binding and leucine-rich repeat gene capture (RenSeq) using a set of approximately 80,000 unique baits on near-isogenic lines, whole-genome resequencing, and bulked segregant analysis to uncover a resistance gene that has remained elusive for 40 years. This work highlights the reassessment of the Rps3b locus from Chr13 to Chr7 and the description of two alleles, from Turkish and Chinese landraces, of a sole candidate gene. We have identified Rps3b in four, fully resequenced, genetic backgrounds, including the original PI from 1985, in which the resistance gene was originally described. Specificity of the resistant alleles was achieved through phenotypic characterization with field isolates carrying virulent and avirulent forms of the corresponding effector, Avr3b. Surprisingly, these alleles showed extremely high synteny and sequence identity with Rps11 consistent with allelism, and conferred a resistance phenotype indistinguishable from that of the recently cloned Rps11. These results offer new sources of resistance for breeders that are effective against the current P. sojae pathotypes in the field.