Role of the Sln1‐phosphorelay pathway in the response to hyperosmotic stress in the yeast Kluyveromyces lactis

Abstract

The Kluyveromyces lactis SLN1 phosphorelay system includes the osmosensor histidine kinase Sln1, the phosphotransfer protein Ypd1 and the response regulator Ssk1. Here we show that K. lactis has a functional phosphorelay system. In vitro assays, using a heterologous histidine kinase, show that the phosphate group is accepted by KlYpd1 and transferred to KlSsk1. Upon hyperosmotic stress the phosphorelay is inactivated, KlYpd1 is dephosphorylated in a KlSln1 dependent manner, and only the version of KlSsk1 that lacks the phosphate group interacts with the MAPKKK KlSsk2. Interestingly, inactivation of the KlPtp2 phosphatase in a ΔKlsln1 mutant did not lead to KlHog1 constitutive phosphorylation. KlHog1 can replace ScHog1p and activate the hyperosmotic response in Saccharomyces cerevisiae, and when ScSln1 is inactivated, KlHog1 becomes phosphorylated and induces cell lethality. All these observations indicate that the phosphorelay negatively regulates KlHog1. Nevertheless, in the absence of KlSln1 or KlYpd1, no constitutive phosphorylation is detected and cells are viable, suggesting that a strong negative feedback that is independent of KlPtp2 operates in K. lactis. Compared with S. cerevisiae, K. lactis has only a moderate accumulation of glycerol and fails to produce trehalose under hyperosmotic stress, indicating that regulation of osmolyte production is different in K. lactis.

Histidine kinase two-component response regulators Ssk1, Skn7 and Rim15 differentially control growth, developmental and volatile organic compounds emissions as stress responses in Trichoderma atroviride

“…In addition, the total lack of growth of Δssk1 under the osmotic stress conditions given by NaCl and Sorbitol ( Fig. 2 ) strongly suggests a direct regulatory role for Ssk1 in this particular type of stress, as previously reported in other fungal models ( Horie et al., 2008 ; Chen et al., 2017 ; Liu et al., 2017 ; Rodriguez-Gonzalez et al., 2017 ). Finally, under the cell wall stress conditions (CW and CR treatments), Δssk1 was the only strain that showed a significant reduction in mycelial growth.…”

Ypd1 Is an Essential Protein of the Major Fungal Pathogen Aspergillus fumigatus and a Key Element in the Phosphorelay That Is Targeted by the Antifungal Drug Fludioxonil

“…This concept is corroborated by the finding that YPD 1 deletions in S. cerevisiae or Cryptococcus neoformans are not lethal in strains, in which the HOG pathway is inactivated by an additional mutation (Posas et al, 1996 ; Lee et al, 2011 ). The fact that some Ypd1p orthologs are not essential (Nguyen et al, 2000 ; Lee et al, 2011 ; Mavrianos et al, 2014 ; Jacob et al, 2015 ; Rodríguez-González et al, 2017 ) points to differences in the Ypd1-dependent signaling processes in different fungi.…”

Involvement of a Response Regulator VdSsk1 in Stress Response, Melanin Biosynthesis and Full Virulence in Verticillium dahliae

“…Although orthologs of Ssk1 are highly conserved among yeasts and filamentous fungi, contradictory roles in the adaption of various stresses are found in several fungi. For example, deletion of Ssk1 in Kluyveromyces lactis does not affect sensitivity to hyperosmotic stress (Rodriguez-Gonzalez et al, 2017). However, disruption of Ssk1 from Candida albicans causes increased sensitivity in the high salinity conditions (Chauhan et al, 2003).…”