The putative four-transmembrane proteins RWTD1 and PRM1 differentially regulate sexual mating, symptom development, and teliospore formation in the sugarcane smut fungus
Sugarcane smut, caused by Sporisorium scitamineum, is one of the most devastating diseases of sugarcane worldwide, leading to severe yield losses and long-term agricultural impacts. Integral membrane proteins are essential components of plasma membranes, playing critical roles in molecular transport, signal transduction, pathogenesis, and defense. However, their contributions to sexual mating and pathogenicity in smut fungi remain largely unknown. In this study, we sought to characterize two novel integral membrane proteins—regulation of whip and teliospore development 1 (RWTD1) and pheromone-regulated multispanning membrane protein (PRM1)—in S. scitamineum. The RWTD1 protein, which contains four transmembrane domains, showed mating-specific upregulation and localized to discrete puncta in the cytoplasm near the cell membrane. The deletion of RWTD1 in Mat-1 haploids abolished filamentous growth after sexual mating, whereas its deletion in Mat-2 haploids resulted in reduced filamentation. Transcriptome profiling revealed that, relative to the wild type, genes encoding several integral and intrinsic membrane components were differentially expressed in RWTD1 mutants, including PRM1 and DIK6, which encode putative four- and seven-transmembrane domain proteins, respectively. Deleting PRM1 recapitulated the mating defects observed in the ΔRWTD1 mutants. While RWTD1, PRM1, and DIK6 contributed to virulence, RWTD1 also functioned in symptom development and teliospore formation. Overall, our work demonstrated that the transmembrane proteins RWTD1, PRM1, and DIK6 are important contributors to virulence and sexual mating in the sugarcane smut fungus.