Abstract
Erythritol production is a unique response to hyperosmotic stress that is observed in a small group of yeasts, including Yarrowia lipolytica. This study investigated whether this unusual mechanism is regulated by the HOG pathway, well described in Saccharomyces cerevisiae. The gene YALI0E25135g was identified as the Y. lipolytica homologue of HOG1 and was found to be phosphorylated in response to hyperosmotic shock. Deletion of the gene caused a significant decrease in resistance to hyperosmotic stress and negatively affected erythritol production. Interestingly, the deletion strain yl-hog1Δ displayed significant morphological defects, with the cells growing in a filamentous form. Moreover, yl-hog1Δ cells were also resistant to the cell wall damaging agents Congo red and calcofluor white. Collectively, these results indicate that yl-Hog1 is crucial for the cellular response to hyperosmotic stress, plays a role in the induction of erythritol production, and potentially prevents cross-talk with different MAPK signalling pathways in the cell.
Highlights
Yarrowia lipolytica is an unconventional, dimorphic yeast with great potential for industrial applications
Phosphorylation of Hog[1] is carried out by the upstream Pbs[2] Mitogen activated protein kinase (MAPK) kinase (MAPKK), which in turn is activated by phosphorylation which is mediated by one of three MAPKK kinases (MAPKKKs): Ste[11], Ssk[2] or Ssk[22] (Fig. 1)
Based on BLAST comparisons with S. cerevisiae and C. albicans HOG1 sequences, the gene YALI0E25135g was identified as the Y. lipolytica homologue of Hog[1]
Summary
Yarrowia lipolytica is an unconventional, dimorphic yeast with great potential for industrial applications. Considering the high interest in this yeast for industrial purposes, it is surprising that very little is known about the regulation of metabolic and signalling pathways This lack of knowledge was recognized during attempts to optimize erythritol production[5,6]. In Candida albicans, the Sho1-Ste[11] branch does not relay osmotic stress signals to Hog[1] This is mediated solely by the Ssk[2] MAPKKK, which is regulated by both Sln[1] dependent and independent mechanisms[16], while the extremely halotolerant Hortaea werneckii has two redundant Hog[1] homologues[17]. Some phenotypes observed in S. cerevisiae hog1Δ mutants are due to the inappropriate activation of alternative MAPKs
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