The transmembrane protein S ho1 cooperates with the mucin M sb2 to regulate invasive growth and plant infection in F usarium oxysporum

Summary In the vascular wilt pathogen F usarium oxysporum , the mitogen‐activated protein kinase ( MAPK ) F mk1 is essential for plant infection. The mucin‐like membrane protein M sb2 regulates a subset of F mk1‐dependent functions. Here, we examined the role of the tetraspan transmembrane protein Sho1 as an additional regulator of the F mk1 pathway and determined its genetic interaction with M sb2. Targeted Δ sho1 mutants were generated in wild‐type and Δ msb2 backgrounds to test possible interactions between the two genes. The mutants were examined for hyphal growth under different stress conditions, phosphorylation of the MAPK F mk1 and an array of F mk1‐dependent virulence functions. Similar to M sb2, Sho1 was required for the activation of F mk1 phosphorylation, as well as F mk1‐dependent gene expression and invasive growth functions, including extracellular pectinolytic activity, cellophane penetration, plant tissue colonization and virulence on tomato plants. Δ sho1 mutants were hypersensitive to the cell wall‐perturbing compound Calcofluor White, and this phenotype was exacerbated in the Δ msb2 Δ sho1 double mutant. These results highlight that S ho1 and M sb2 have partially overlapping functions upstream of the F mk1 MAPK cascade, to promote invasive growth and plant infection, as well as cell wall integrity, in F . oxysporum .