Trehalose pathway regulates filamentation response in Saccharomyces cerevisiae

In Saccharomyces cerevisae , the diploid cells undergo either pseudohyphal differentiation or sporulation in response to carbon and nitrogen source depletion. Distinct pathways are known to regulate the processes of filamentation and sporulation in response to nutritional stress. Here, we report the novel finding that the trehalose pathway which is essential for sporulation, is involved in pseudohyphae formation both via GPR1 as well as RAS2 mediated signaling. Our observations indicate that GPR1 is epistatic over TPS1 in signaling for filamentation. Further, we have demonstrated that the pseudohyphal defect of the ras2 mutant is overcome upon disruption of TPS2 . Thus, our results indicate that TPS1 and TPS2 may be involved in cell fate decision between meiosis and filamentation response under nutrient depleting conditions. Further, monitoring pseudohyphae formation under limiting glucose condition unravelled the possibility that TPS1 and TPS2 exert opposing effects to trigger filamentation response.

Pseudohyphal differentiation in Komagataella phaffii: investigating the FLO gene family

ABSTRACT Many yeasts differentiate into multicellular phenotypes in adverse environmental conditions. Here, we investigate pseudohyphal growth in Komagataella phaffii and the involvement of the flocculin (FLO) gene family in its regulation. The K. phaffii FLO family consists of 13 members, and the conditions inducing pseudohyphal growth are different from Saccharomyces cerevisiae. So far, this phenotype was only observed when K. phaffii was cultivated at slow growth rates in glucose-limited chemostats, but not upon nitrogen starvation or the presence of fusel alcohols. Transcriptional analysis identified that FLO11, FLO400 and FLO5-1 are involved in the phenotype, all being controlled by the transcriptional regulator Flo8. The three genes exhibit a complex mechanism of expression and repression during transition from yeast to pseudohyphal form. Unlike in S. cerevisiae, deletion of FLO11 does not completely prevent the phenotype. In contrast, deletion of FLO400 or FLO5-1 prevents pseudohyphae formation, and hampers FLO11 expression. FAIRE-Seq data shows that the expression and repression of FLO400 and FLO5-1 are correlated to open or closed chromatin regions upstream of these genes, respectively. Our findings indicate that K. phaffii Flo400 and/or Flo5-1 act as upstream signals that lead to the induction of FLO11 upon glucose limitation in chemostats at slow growth and chromatin modulation is involved in the regulation of their expression.

Roles of the Snf1-Activating Kinases during Nitrogen Limitation and Pseudohyphal Differentiation in Saccharomyces cerevisiae

ABSTRACT In Saccharomyces cerevisiae, Snf1 protein kinase is important for growth on carbon sources that are less preferred than glucose. When glucose becomes limiting, Snf1 undergoes catalytic activation, which requires phosphorylation of its T-loop threonine (Thr210). Thr210 phosphorylation can be performed by any of three Snf1-activating kinases: Sak1, Tos3, and Elm1. These kinases are redundant in that all three must be eliminated to confer snf1Δ-like growth defects on nonpreferred carbon sources. We previously showed that in addition to glucose signaling, Snf1 also participates in nitrogen signaling and is required for diploid pseudohyphal differentiation, a filamentous-growth response to nitrogen limitation. Here, we addressed the roles of the Snf1-activating kinases in this process. Loss of Sak1 caused a defect in pseudohyphal differentiation, whereas Tos3 and Elm1 were dispensable. Sak1 was also required for increased Thr210 phosphorylation of Snf1 under nitrogen-limiting conditions. Expression of a catalytically hyperactive version of Snf1 restored pseudohyphal differentiation in the sak1Δ/sak1Δ mutant. Thus, while the Snf1-activating kinases exhibit redundancy for growth on nonpreferred carbon sources, the loss of Sak1 alone produced a significant defect in a nitrogen-regulated phenotype, and this defect resulted from deficient Snf1 activation rather than from disruption of another pathway. Our results suggest that Sak1 is involved in nitrogen signaling upstream of Snf1.

Amino acids mediate colony and cell differentiation in the fungal pathogen Candida parapsilosis

Candida parapsilosis is responsible for severe cases of non-albicans systemic candidiasis and is one of the leading causes of mortality in neonates. The molecular mechanisms underlying this organism's virulence remain unknown. Unlike C. albicans, which can exist in several morphogenetic forms, C. parapsilosis exists in either the yeast or pseudohyphal forms. The environmental signals that trigger pseudohyphal differentiation and the signalling pathways that transduce these signals are unknown. This paper provides evidence for the role of amino acids in morphogenesis in C. parapsilosis. The cell and colony morphologies, pseudohyphal differentiation and invasive growth of five C. parapsilosis isolates were characterized in ammonium-rich minimal media lacking or supplemented with naturally occurring amino acids. C. parapsilosis underwent dramatic changes in cellular and colony morphology and formed pseudohyphae in response to a specific subset of amino acids. Transport studies showed that these amino acid inducers activate the transport of some, but not all, unrelated amino acids. Interestingly, citrulline, an amino acid that is not transported in the presence of ammonium, strongly induced pseudohyphal morphogenesis in C. parapsilosis under these conditions. Together the data suggest that amino acids are important morphogens in C. parapsilosis and that amino-acid-mediated morphogenesis in this organism does not require transport of the ligand across the plasma membrane.