Abstract
Potassium has an important role to play in multiple cellular processes. In Saccharomyces cerevisiae, the serine/threonine (S/T) kinase Sat4/Hal4 is required for potassium accumulation, and thus, regulates the resistance to sodium salts and helps in the stabilization of other plasma membrane transporters. However, the functions of Sat4 in filamentous phytopathogenic fungi are largely unknown. In this study, ChSat4, the yeast Sat4p homolog in Colletotrichum higginsianum, has been identified. Target deletion of ChSAT4 resulted in defects in mycelial growth and sporulation. Intracellular K+ accumulation was significantly decreased in the ChSAT4 deletion mutant. Additionally, the ΔChsat4 mutant showed defects in cell wall integrity, hyperoxide stress response, and pathogenicity. Localization pattern analysis indicated ChSat4 was localized in the cytoplasm. Furthermore, ChSat4 showed high functional conservation with the homolog FgSat4 in Fusarium graminearum. Taken together, our data indicated that ChSat4 was important for intracellular K+ accumulation and infection morphogenesis in C. higginsianum.
Highlights
Potassium is indispensable for multiple cellular processes, wherein it has important roles in the maintenance of the membrane potential and intracellular pH, and regulation of cellular enzyme activity (Kahm et al, 2012)
We show that ChSat4 is involved in K+ accumulation, but is important for hyphal growth, sporulation, cell wall integrity, and pathogenicity
Phylogenetic analysis showed that the Sat4 proteins in filamentous fungi have diverged from those of unicellular yeasts, and ChSat4 of C. higginsianum and other Sat4 proteins from Colletotrichum formed a monophyletic lineage (Supplementary Figure S1A)
Summary
Potassium is indispensable for multiple cellular processes, wherein it has important roles in the maintenance of the membrane potential and intracellular pH, and regulation of cellular enzyme activity (Kahm et al, 2012). In S. cerevisiae, SAT4 encodes a serine/threonine kinase, which positively regulates potassium uptake through a Trk1p-dependent manner (Mulet et al, 1999) This protein contributes to the stabilization of the plasma membrane transporters, the control of carbon and nitrogen metabolism, and the regulation of the transcriptional activator Gln (Mulet et al, 1999; Pérez-Valle et al, 2010; Hirasaki et al, 2011). In the filamentous fungus Fusarium graminearum, the deletion of FgSAT4 inhibited hyphal growth and sporulation, altered the normal conidial morphology, increased the sensitivity to NaCl, and decreased the pathogenicity to the host plant (Wang et al, 2011; Zheng et al, 2012) These observations indicated that SAT4 and its orthologs may share different functions and regulatory mechanisms in S. cerevisiae and phytopathogenic fungi
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