Fine-mapping and evolutionary history of R-BPMV, a dominant resistance gene to Bean pod mottle virus in Phaseolus vulgaris L.

Abstract

R-BPMV is located within a recently expanded TNL cluster in the Phaseolus genus with suppressed recombination and known for resistance to multiple pathogens including potyviruses controlled by the I gene. Bean pod mottle virus (BPMV) is a comovirus that infects common bean and legumes in general. BPMV is distributed throughout the world and is a major threat on soybean, a closely related species of common bean. In common bean, BAT93 was reported to carry the R-BPMV resistance gene conferring resistance to BPMV and linked with the I resistance gene. To fine map R-BPMV, 182 recombinant inbred lines (RILs) derived from the cross BAT93 × JaloEEP558 were genotyped with polymerase chain reaction (PCR)-based markers developed using genome assemblies from G19833 and BAT93, as well as BAT93 BAC clone sequences. Analysis of RILs carrying key recombination events positioned R-BPMV to a target region containing at least 16 TIR-NB-LRR (TNL) sequences in BAT93. Because the I cluster presents a suppression of recombination and a large number of repeated sequences, none of the 16 TNLs could be excluded as R-BPMV candidate gene. The evolutionary history of the TNLs for the I cluster were reconstructed using microsynteny and phylogenetic analyses within the legume family. A single I TNL was present in Medicago truncatula and lost in soybean, mirroring the absence of complete BPMV resistance in soybean. Amplification of TNLs in the I cluster predates the divergence of the Phaseolus species, in agreement with the emergence of R-BPMV before the separation of the common bean wild centers of diversity. This analysis provides PCR-based markers useful in marker-assisted selection (MAS) and laid the foundation for cloning of R-BPMV resistance gene in order to transfer the resistance into soybean.