The response regulator BcSkn7 is required for vegetative differentiation and adaptation to oxidative and osmotic stresses in Botrytis cinerea

Abstract

The high-osmolarity glycerol pathway plays an important role in the responses of fungi to various environmental stresses. Saccharomyces cerevisiae Skn7 is a response regulator in the high-osmolarity glycerol pathway, which regulates the oxidative stress response, cell cycle and cell wall biosynthesis. In this study, we characterized an Skn7 orthologue BcSkn7 in Botrytis cinerea. BcSKN7 can partly restore the growth defects of S. cerevisiae SKN7 mutant and vice versa. The BcSKN7 mutant (ΔBcSkn7-1) revealed increased sensitivity to ionic osmotic and oxidative stresses and to ergosterol biosynthesis inhibitors. In addition, ΔBcSkn7-1 was also impaired dramatically in conidiation and sclerotial formation. Western blot analysis showed that BcSkn7 positively regulated the phosphorylation of BcSak1 (the orthologue of S. cerevisiae Hog1) under osmotic stress, indicating that BcSkn7 is associated with the high-osmolarity glycerol pathway in B. cinerea. In contrast with BcSak1, BcSkn7 is not involved in the regulation of B. cinerea virulence. All of the phenotypic defects of ΔBcSkn7-1 are restored by genetic complementation of the mutant with the wild-type BcSKN7. The results of this study indicate that BcSkn7 plays an important role in the regulation of vegetative differentiation and in the response to various stresses in B. cinerea.

Unraveling the Function of the Response Regulator BcSkn7 in the Stress Signaling Network of Botrytis cinerea

“…A comparison of the results shows that there are several differences between the phenotypes of the ⌬bcskn7 mutants, starting with a divergent gene annotation. In contrast to six introns confirmed by cDNA sequencing in the ORF of bcskn7 in this study, only four introns are described in Yang et al (32). Moreover, the results concerning formation of reproductive structures, sensitivity to cell wall stress, and virulence differ.…”

“…Therefore, an additional effector pathway for Bos1 is assumed (26). This pathway probably involves the second response regulator BcSkn7, which was recently identified and partly characterized in a parallel investigation (32). It was shown that under osmotic stress BcSkn7 positively regulated phosphorylation of BcSak1; however, phosphorylation and expression analyses showed that regulation of the oxidative stress response probably is independent of BcSak1 phosphorylation, in a similar manner to that observed in yeast.…”

“…Moreover, the results concerning formation of reproductive structures, sensitivity to cell wall stress, and virulence differ. However, one has to keep in mind that Yang et al (32) worked with the B. cinerea strain 38B1, while B05.10 was used in this study. There are some reports that gene deletions can have diverse impacts on growth and virulence in B. cinerea in distinct strain backgrounds.…”

MrSkn7 Controls Sporulation, Cell Wall Integrity, Autolysis, and Virulence in Metarhizium robertsii

“…We also found that the ⌬MrSkn7 mutant completely lost the ability to produce conidia on PDA, while the conidiation abilities were only partially impaired in the BcSkn7 deletion mutant of B. cinerea (9), ⌬FgSkn7 mutant of F. graminearum (8), and ⌬SrrA (i.e., ⌬AnSkn7) mutant of A. nidulans (36). Salt stress could induce the upregulation of sporulation-related genes (Fig.…”

“…The orthologs of Skn7 in yeasts and different filamentous fungi generally contribute to cell wall integrity, sporulation, osmotic stress, and oxidative stress (5). Interestingly, deletion of MoSkn7 (Magnaporthe oryzae Skn7) in M. oryzae (7), FgSkn7 (Fusarium graminearum Skn7) in F. graminearum (8), and BcSkn7 (Botrytis cinerea Skn7) in B. cinerea (9) did not impair fungal virulence and thereby the ability to infect their respective plant hosts. In contrast, AaSkn7 (Alternaria alternata Skn7) is required by A. alternata to infect citrus (10).…”