Abstract
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.
Highlights
Necrotrophic diseases negatively affect the production of numerous species of crops, vegetables, fruit trees, and pastures, including the major food staples in the world—rice, corn, and wheat (Sneh et al, 1991; Staats et al, 2005; Michielse and Rep, 2009)
The national standard strain of R. solani AG1 IA was precultured in potato sucrose agar (PSA) medium, and small pieces of agar block with fresh R. solani mycelia were transferred into potato sucrose broth (PSB) medium (200 g/L boiled potato extract and 20 g/L sucrose) to amplify the mycelia
To select 10 small cysteine-rich (SCR) to focus on (Supplementary Table 1). cDNAs for these genes were successfully cloned from the national standard strain of R. solani AG1 IA, and their molecular functions were examined by agroinfiltration-based bioassays in model plant N. benthamiana
Summary
Necrotrophic diseases negatively affect the production of numerous species of crops, vegetables, fruit trees, and pastures, including the major food staples in the world—rice, corn, and wheat (Sneh et al, 1991; Staats et al, 2005; Michielse and Rep, 2009). A basidiomycete species complex, Rhizoctonia solani is a phytopathogen that exhibits a broad host range and is problematic for farmers, in tropical areas with high humidity (Ogoshi, 1987; Taheri and Tarighi, 2011). R. solani releases various molecular proteins, such as phytotoxins, carbohydrate-active enzymes, and effector proteins, during infection of plant hosts to achieve colonization. Among these proteins, effectors in R. solani are the least studied. Numerous candidate effector molecules have been predicted in the genome and transcriptome sequences of R. solani
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