No safe haven: Loss of avirulence in the plant pathogen Leptosphaeria maculans by DNA duplication and repeat‐induced point mutation

Microbes can overcome the ability of plant resistance genes to confer protection against disease by mutating their corresponding avirulence genes. The fungus Leptosphaeria maculans causes blackleg disease on canola crops and subverts Brassica napus resistance genes through several DNA mutation mechanisms. One of these is repeat‐induced point (RIP) mutation, which can ‘leak’ into the avirulence genes from the adjacent repetitive sequences that the mutation process is targeting. Here, we identified populations of L. maculans in Australia that have extensive RIP mutations in the avirulence gene AvrLm2 and show that this has been triggered by a duplication of the gene and surrounding DNA that includes the distant (>55 kb in total) AvrLm6 gene. This finding provides another mechanism of mutation by which pathogens can overcome host resistance, and more broadly contributes to understanding the complex balance between gene duplication and genome defence.