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.

A Novel, Small Cysteine-Rich Effector, RsSCR10 in Rhizoctonia solani Is Sufficient to Trigger Plant Cell Death.

The necrotrophic phytopathogen Rhizoctonia solani (R. solani) is a fungus that causes disease in a wide range of plant species. Fungal genomes encode abundant, small cysteine-rich (SCR) secreted proteins, and the probable importance of these to pathogenesis has been highlighted in various pathogens. However, there are currently no reports of an R. solani SCR-secreted protein with evidential elicitor activity. In this study, the molecular function of 10 SCR-secreted protein genes from R. solani was explored by agroinfiltration into Nicotiana benthamiana (N. benthamiana) leaves, and a novel SCR protein RsSCR10 was identified that triggered cell death and oxidative burst in tobacco. RsSCR10 comprises 84 amino acids, including a signal peptide (SP) of 19 amino acids that is necessary for RsSCR10 to induce tobacco cell death. Elicitation of cell death by RsSCR10 was dependent on Hsp90 but not on RAR1, proving its effector activity. Two cysteine residues have important effects on the function of RsSCR10 in inducing cell death. Furthermore, RsSCR10 showed cross-interaction with five rice molecules, and the inferred functions of these rice proteins suggest they are instrumental in how the host copes with adversity. Overall, this study demonstrates that RsSCR10 is a potential effector that has a critical role in R. solani AG1 IA-host interactions.