The blast effector Pwl2 is a virulence factor that modifies the cellular localisation of host protein HIPP43 to suppress immunity.

The rice blast fungusMagnaporthe oryzaesecretes a battery of effector proteins during host infection to suppress plant immunity and promote disease. Among these effectors, the MAX effector-Pwl2 was first identified as a host specificity determinant for infection of weeping lovegrass (Eragrostis curvula). However, its biological activity has remained unknown. Here we show that thePWL2gene is ubiquitous in all host-limited forms ofM. oryzaeand has undergone substantial copy number expansion indicating that it is a core effector of the blast fungus. We used CRISPR/Cas9-mediated gene editing to delete all three copies ofPWL2and generate apwl2null mutant inM. oryzaestrain Guy11. This resulted in gain-of-virulence towards weeping lovegrass, but a reduction in the severity of disease symptoms on rice. To further investigate the virulence mechanism of Pwl2, we showed that transgenic rice and barley lines constitutively expressingPWL2display suppression of reactive oxygen species generation and increased susceptibility to infection byM. oryzae. Also, we identify the barley and rice heavy metal-binding isoprenylated protein HIPP43 as a target of the Pwl2 effector. Transgenic lines overexpressing HIPP43 exhibit attenuated defense responses and increased susceptibility to blast infection, consistent with the hypothesis that Pwl2 binds HIPP43 to modulate immunity. This binding is coupled to changes in cellular localisation of these proteins. Taken together, our results provide evidence that Pwl2 is a virulence factor inM. oryzaethat acts by suppressing host immunity through binding and re-localising HIPP43.