Abstract
Verticillium dahliae causes vascular wilt disease on over 200 plant species worldwide. This fungus forms melanized microsclerotia which help it to survive under adverse conditions and these structures are vital to the disease spread. Here, we identified and characterized a V. dahliae homolog to of the Saccharomyces cerevisiae Ssk1, a response regulator of the two-component system. Herein, we demonstrated that the VdSsk1 deletion strains were more sensitive to various stresses, including oxidative stress conferred by H2O2 and sodium nitroprusside dihydrate, while the mutants confered higher resistance to fungicides such as fludioxonil and iprodione. Furthermore, disruption of VdSsk1 resulted in significant downregulation of melanin biosynthesis-related genes but did not affect microsclerotial development. Phosphorylation of VdHog1 was not detected in the VdSsk1 deletion strains under the treatment of sorbitol, indicating that phosphorylation of VdHog1 is dependent on VdSsk1. Finally, we demonstrated that VdSsk1 is required for full virulence. Taken together, this study suggests that VdSsk1 modulates stress response, melanin biosynthesis and virulence of V. dahliae.
Highlights
The two-component system (TCS) pathway is a primary means of responding to external stimuli, and is widely conserved in bacteria, fungi, and plants (Bourret et al, 1991; Alex et al, 1996)
These findings indicate that VdSsk1 governs the signaling required for appropriate stress responses, melanin biosynthesis, and for full virulence in V. dahliae
The potential VdSsk1 deletion strains were screened by genomic PCR and the deletion mutants were confirmed by southern blot (Supplementary Figure S2)
Summary
The two-component system (TCS) pathway is a primary means of responding to external stimuli, and is widely conserved in bacteria, fungi, and plants (Bourret et al, 1991; Alex et al, 1996). Most eukaryotic TCSs always comprise a membrane-bound sensor histidine kinase (HK), a response regulator (RR) and a His-containing phosphotransfer protein (HPt) (Motoyama et al, 2008). In the budding yeast Saccharomyces cerevisiae, the TCS pathway contains one HK (Sln1), one Hpt protein (Ypd1) and two RRs (Ssk and Skn7) (Schaller et al, 2011). The histidine kinase functions as the sensor reacting to external stress signals and activates RRs, which trigger downstream responses including stress signaling pathways and expression of stress response genes. Ssk acts through the HOG MAPK cascade as an upstream regulator in S. cerevisiae, while Skn functions as a stress response transcription factor to adapt to conditions of high osmolarity
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