Brassica napus genes Rlm4 and Rlm7, conferring resistance to Leptosphaeria maculans, are alleles of the Rlm9 wall-associated kinase-like resistance locus

Abstract

Plant cell surface receptors are at the forefront of defence against pathogens, involved in pathogen sensing through the detection of conserved molecules named pathogen-associated molecular patterns (PAMP) and highly variable pathogen virulence (effector) proteins. The recently reported Brassica napus (canola, oilseed rape) disease resistance gene Rlm9 encodes a wall-associated kinase-like (WAKL) receptor which confers race-specific resistance against races of the blackleg pathogen Leptosphaeria maculans carrying the corresponding effector gene, AvrLm5-9 (Larkan et al., 2020). Rlm4 and Rlm7 are located on B. napus chromosome A07 and genetically tightly linked to Rlm9 (Larkan et al., 2016). The L. maculans effectors AvrLm4-7 and AvrLm7 are small, secreted cysteine-rich proteins encoded by a single locus, AvrLm4-7. A single amino acid change in AvrLm4-7 masks recognition by Rlm4 without affecting Rlm7 function. Here, we report the cloning of Rlm4 and Rlm7, both alleles of the Rlm9 WAKL locus.