P-214 - The plasma membrane-localized effector protein SOVIG9 of Sporisorium reilianum supresses defense signaling of Sorghum bicolor

Sporisorium reilianum f.sp. reilianum (SRS) is the causal agent of head smut disease in sorghum. The biotrophic smut fungus infects the plant at the seedling stage and proliferates inside the plant without visible symptoms, successfully suppressing the plant's immune system. Using a classical genetics approach we identified a gene cluster encoding nine effector proteins contributing to the host-specific virulence of SRS on sorghum. We found that the knock-out of the ninth effector, SOVIG9, results in visible plant defense responses including the induction of sorghum-specific phytoalexins on infected leaves, suggesting that the effector suppresses plant defense responses during early infection stages. We proved secretion of SOVIG9 and showed that the effector is myristoylated in planta putatively targeting plasma membrane-associated proteins and thereby suppressing the plant's phospho-signaling. Interestingly, protein-tags or modifications affecting the protein structure of SOVIG9 resulted in an even stronger phytoalexin induction hinting at recognition of the modified effector by the plant's immune system. We are currently identifying the exact target proteins of SOVIG9 as well as putative R proteins recognizing the tagged effector using IP-LC/MS. Understanding the function of the SOVIG9 effector of S. reilianum will give new insights on effector-mediated host-adaptation in plant-pathogen interactions.