Explorations of a novel effector CcAA9-20333 from Colletotrichum coccodes: the potential roles played in host immunity.

Key message: The AA9 LMPO protein, CcAA9-20333, acts as a secretory effector by inhibiting N. benthamiana cell death via its enzymatic activity and contributes to the virulence of C. coccodes. Although the functions of most effectors produced by fungi are unclear, it is known that they may both increase infection and alter host immunity. This research describes a novel fungal effector protein CcAA9-20333 of Colletotrichum coccodes. First, the signal peptide of CcAA9-20333 has secretory function verified by yeast trap secretion assay and subcellular localization, and CcAA9-20333 with the full length can inhibit host immunity including the PCD induced by INF1 and BAX, accumulation of ROS, ion leakage, and genes' expression involved in SA and JA pathway, and even inhibit the susceptibility of plant to C. coccodes. The expression level of CcAA9-20333 was associated with the regulation mechanism of it on immune response, with the positive correlation. In addition, all of these functions were decided by the enzymatic activity of CcAA9-20333, which was verified by site mutant. The morphological characteristics of ΔCcAA9-20333, the mutant of C. coccodes, demonstrated that CcAA9-20333 can reduce the sporulation and virulence. All of these provided that CcAA9-20333 play a critical role in regulating the immunity of host plant and pathogenicity of C. coccodes. This approach teaches us to see beyond the obvious while expanding the field of LPMO study.