The PP2A phosphatase regulatory subunit SsRts1 regulates morphogenesis, mitosis, sexual mating and virulence in Sporisorium scitamineum

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Sugarcane smut, caused by S. scitamineum, results in substantial economic losses across global sugarcane growing areas. Elucidating the pathogenic mechanisms of S. scitamineum is therefore crucial for developing effective disease control strategies. Our previous work has shown that the protein phosphatase SsPpe1 regulates mating and pathogenicity in S. scitamineum. In this study, we identified SsRts1 as a novel interacting protein of SsPpe1, which contains a PP2A regulator subunit B56 domain. Deletion of Ssrts1 gene impaired sporidia growth, resulting in pseudohyphal sporidia with multiple nuclei and aberrant chitin distribution. Further analysis revealed elevated phosphorylation levels of the cell cycle-related kinase CDK1T161 in the ΔSsrts1 mutants, suggesting that SsRts1 participates in mitosis regulation. Moreover, the ΔSsrts1 mutants exhibited increased sensitivity to cell wall, oxidative and high osmotic stresses. Mechanistically, SsRts1 negatively regulates the phosphorylation levels of the CWI-MAPK Mps1, implicating that SsRts1 is involved in regulating the cell wall integrity (CWI) pathway. Additionally, deletion of Ssrts1 also led to abnormal accumulation of autophagosome, along with defects in sexual mating, filamentation, and virulence. Global transcriptome profiling indicated that SsRts1 modulates ATPase activity, cell cycle progression, transmembrane transport, and tryptophan metabolism. Notably, exogenous supplementation with tryptophan partially restored the mating and filamentation defects in the ΔSsrts1 mutants, indicating that SsRts1 modulates these processes partly through the tryptophan catabolism pathway. Collectively, these findings provide insight into the regulatory roles of PP2A regulatory subunit SsRts1 in S. scitamineum, and expand our understanding of PP2A function in plant-pathogenic fungi.

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