A small secreted protein, RsMf8HN, in Rhizoctonia solani triggers plant immune response, which interacts with rice OsHIPP28

The necrotrophic phytopathogen Rhizoctonia solani (R. solani) causes disease in many plant species. This fungal genome encodes abundant small cysteine-rich (SCR)-secreted proteins in R. solani that may induce pathogenesis. To test their molecular functions, we introduced 10 SCR-secreted protein genes from R. solani into tobacco leaves via agroinfiltration. Consequently, we identified RsMf8HN, a novel SCR protein that triggers cell death and an oxidative burst in tobacco. RsMf8HN comprises 182 amino acids (aa), including a signal peptide (SP) of 17aa, and the protein has unique features: it is orthologous to an allergen protein Mal f 8 occurring in Malassezia species, and possesses a high glycine and serine content. RsMf8HN is coded in a genomic location along with its paralogues and a few other effector candidates. The elicitation of plant immunity by RsMf8HN was dependent on HSP90 and SGT1. RsMf8HN was translocated to multiple locations within the host cells: i.e., nuclei, chloroplasts, and plasma membranes. We confirmed the occurrence of in vivo cross-interactions of RsMf8HN with a rice molecule, the heavy metal-associated isoprenylated plant protein OsHIPP28, which is a protein related to the disease susceptibility factor Pi21. In summary, our results suggest that RsMf8HN is a potential effector that enables necrotrophic phytopathogens to interfere with host plant immunity.