The Brassica napus wall‐associated kinase‐like (WAKL) gene Rlm9 provides race‐specific blackleg resistance

In plants, race‐specific defence against microbial pathogens is facilitated by resistance (R) genes which correspond to specific pathogen avirulence genes. This study reports the cloning of a blackleg R gene from Brassica napus (canola), Rlm9, which encodes a wall‐associated kinase‐like (WAKL) protein, a newly discovered class of race‐specific plant RLK resistance genes. Rlm9 provides race‐specific resistance against isolates of Leptosphaeria maculans carrying the corresponding avirulence gene AvrLm5‐9, representing only the second WAKL‐type R gene described to date. The Rlm9 protein is predicted to be cell membrane‐bound and while not conclusive, our work did not indicate direct interaction with AvrLm5‐9. Rlm9 forms part of a distinct evolutionary family of RLK proteins in B. napus, and while little is yet known about WAKL function, the Brassica–Leptosphaeria pathosystem may prove to be a model system by which the mechanism of fungal avirulence protein recognition by WAKL‐type R genes can be determined.