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Functional analysis of Mpk1-mediated cell wall integrity signaling pathway in the thermotolerant methylotrophic yeast Hansenula polymorpha

ABSTRACT: Purpose: To identify the downstream gene sets regulated by Mpk1p in H. polymorpha under normal and caffeine-treated conditions, we compared the RNA-seq based transcriptional profiles. Methods: Total RNA was isolated according to the hot phenol extraction method and all procedure for RNA sequencing were conducted by ChunLab. More than 1.5-fold regulated genes are functionally classified using the Munich Information Center for Protein Sequences (MIPS) FunCat. Results: Transcriptome analysis of the DL1-L strain revealed that caffeine significantly increased expression of a subset of cell-wall related genes in an Mpk1p-dependent manner, but most of which were not Rlm1-target genes. Conclusion: Our results support the essential role of Mpk1p in maintaining cell wall integrity upon several stress conditions of H. polymorpha.

ORGANISM(S): Ogataea parapolymorpha

PROVIDER: GSE106861 | GEO | 2018/11/14

REPOSITORIES: GEO

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Project description:Caffeine is a natural purine analog that elicits pleiotropic effects, which ultimately lead to cell death by a mechanism that is still largely uncharacterized. This drug can activate the PKC1-MAPK cell integrity pathway, as shown by phosphorylation of Mpk1 kinase. However, and contrary to expectation, the caffeine-induced hyperphosphorylation of Mpk1 was accompanied by a negligible activation of its downstream targets Rlm1 and SBF transcription factors, which suggested that the fortification of the cell wall induced by caffeine was independent on the MAP kinase activation. This result was consistent with the finding that the loss of RLM1 had no consequence on the increased resistance of caffeine-treated cells to zymolyase, and was further consolidated by a genome-wide microarray analysis showing that, contrary to the cell wall drugs Congo Red and Calcofluor white, caffeine did not cause upregulation of Rlm1-dependent genes encoding cell wall remodeling enzymes. Interestingly, this global expression analysis revealed a striking resemblance of the transcriptomic responses to caffeine with those of rapamycin, a potent inhibitor of the TOR1 and TOR2 kinases. Consistent with this analysis, we found that the caffeine-induced phosphorylation of Mpk1 was lost in a tor1(delta) mutant but it was conserved in a TOR1-1 strain bearing a rapamycin-insensitive Tor1 kinase. Also, and contrary to the mechanism by which rapamycin led to activation of the PKC pathway, the caffeine-dependent process did not necessitate cell wall sensors and was completely abolished upon deletion of ROM2 encoding a GDP/GTP exchange factor of the Rho1-PKC pathway. Moreover, addition of caffeine to yeast cells resulted in a transient drop in intracellular cAMP, and this effect was not observed in a rom2(delta) mutant. In summary, our results revealed that Tor1 is a potential direct target of caffeine in yeast, whose inhibition leads to activation of the Pkc1-Mpk1 kinase cascade and inhibition of the Ras/cAMP pathway, and that for this specific case, the cross-talk between these signaling pathways is mediated by Rom2. These results may have broad implication for our understanding of caffeine effects in analogous regulatory networks in mammalian cells. Key words: caffeine, antifungal drugs, cell wall, transcript profiling, TOR, PKC1, RAS/cAMP. Keywords: time course, dose response

Project description:BackgroundOgataea (Hansenula) polymorpha is one of the most thermotolerant xylose-fermenting yeast species reported to date. Several metabolic engineering approaches have been successfully demonstrated to improve high-temperature alcoholic fermentation by O. polymorpha. Further improvement of ethanol production from xylose in O. polymorpha depends on the identification of bottlenecks in the xylose conversion pathway to ethanol.ResultsInvolvement of peroxisomal enzymes in xylose metabolism has not been described to date. Here, we found that peroxisomal transketolase (known also as dihydroxyacetone synthase) and peroxisomal transaldolase (enzyme with unknown function) in the thermotolerant methylotrophic yeast, Ogataea (Hansenula) polymorpha, are required for xylose alcoholic fermentation, but not for growth on this pentose sugar. Mutants with knockout of DAS1 and TAL2 coding for peroxisomal transketolase and peroxisomal transaldolase, respectively, normally grow on xylose. However, these mutants were found to be unable to support ethanol production. The O. polymorpha mutant with the TAL1 knockout (coding for cytosolic transaldolase) normally grew on glucose and did not grow on xylose; this defect was rescued by overexpression of TAL2. The conditional mutant, pYNR1-TKL1, that expresses the cytosolic transketolase gene under control of the ammonium repressible nitrate reductase promoter did not grow on xylose and grew poorly on glucose media supplemented with ammonium. Overexpression of DAS1 only partially restored the defects displayed by the pYNR1-TKL1 mutant. The mutants defective in peroxisome biogenesis, pex3Δ and pex6Δ, showed normal growth on xylose, but were unable to ferment this sugar. Moreover, the pex3Δ mutant of the non-methylotrophic yeast, Scheffersomyces (Pichia) stipitis, normally grows on and ferments xylose. Separate overexpression or co-overexpression of DAS1 and TAL2 in the wild-type strain increased ethanol synthesis from xylose 2 to 4 times with no effect on the alcoholic fermentation of glucose. Overexpression of TKL1 and TAL1 also elevated ethanol production from xylose. Finally, co-overexpression of DAS1 and TAL2 in the best previously isolated O. polymorpha xylose to ethanol producer led to increase in ethanol accumulation up to 16.5 g/L at 45 °C; or 30-40 times more ethanol than is produced by the wild-type strain.ConclusionsOur results indicate the importance of the peroxisomal enzymes, transketolase (dihydroxyacetone synthase, Das1), and transaldolase (Tal2), in the xylose alcoholic fermentation of O. polymorpha.

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Functional analysis of Mpk1-mediated cell wall integrity signaling pathway in the thermotolerant methylotrophic yeast Hansenula polymorpha

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