Role of the Sln1‐phosphorelay pathway in the response to hyperosmotic stress in the yeast Kluyveromyces lactis
Summary 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 th...
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Veröffentlicht in: | Molecular microbiology 2017-06, Vol.104 (5), p.822-836 |
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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.
The osmotic stress response in yeast requires the Sln1/Ypd1/Ssk1 phosphorelay system. In Saccharomyces cerevisiae, inactivation of Sln1 leads to constitutive Hog1 phosphorylation and to cell lethality due to hyperactivation of the HOG pathway. In this condition, the Ptp2 phosphatase, which dephosphorylates Hog1, would be insufficient to attenuate Hog1 activity. In contrast, in Kluyveromyces lactis, a strong feedback mechanism, independent on Ptp2, is operating and will inactivate Hog1 in a mutant lacking Sln1. |
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ISSN: | 0950-382X 1365-2958 |
DOI: | 10.1111/mmi.13664 |