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Komagataella phaffii encodes two Pho4 transcription factors: a comparative functional study under phosphate starvation and high pH stress

ABSTRACT: The transcription factor Pho4 plays a crucial role in the response to phosphate starvation in many fungi, and it has been linked to tolerance to alkalinization of the medium. The vast majority of fungi encode a single Pho4-encoding gene. However, the genome of the industrially relevant yeast Komagataella phaffii appears to encode two possible Pho4 proteins, namely PAS-chr1-1_0265 and PASchr2-1_0177, designated here PHO4(A) and PHO4(B), respectively, which have never been functionally characterized. Phenotypic analysis of single and double mutants suggests that Pho4(B) plays a major role in adaptation to Pi scarcity. The phenotypes of single mutants do not overlap, but the double mutant is sensitive to multiple types of stress, including alkaline pH. Transcriptomic analysis under Pi starvation confirms that Pho4(B) is crucial for the typical transcriptional response (induction of PHO5, PHO89, VTC1, etc.). However, under high pH stress, induction of many of these genes becomes also PHO4(A) dependent, at least in the short-time response. Notably, expression of both PHO4(A) and PHO4(B) allows growth of a S. cerevisiae pho4 deletion mutant in the absence of phosphate. These results suggest that both transcription factors are functional in K. phaffii, although their functions are only partially overlapping, that these genes can respond differently to diverse stimuli, and that together are a key component in the adaptation to a variety of stresses.

ORGANISM(S): Komagataella phaffii GS115

PROVIDER: GSE310523 | GEO | 2026/07/24

REPOSITORIES: GEO

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Project description:Binding of transcription factors to DNA is a key regulatory step in the control of gene expression. DNA sequences with high affinity for transcription factors occur more frequently in the genome than instances of genes bound or regulated by these factors. How specific gene regulation is achieved by transcription factors remains unclear. We used genome-wide approaches to study how trans factors shape the binding and regulatory landscape of Pho4, a budding yeast transcription factor that activates gene expression in response to phosphate limitation. In no phosphate (0mM phosphate) medium, Pho4 is transported into the nucleus and activates transcription of a set of genes (PHO) that are necessary for cell survival in phosphate limited environment. In high phosphate (10mM phosphate) medium, Pho4 is transported outside of the nucleus and the transcription program of PHO genes are turned off. Here we examined the transcription profiling of S. cerevisiae (W303) in various strains treated in media with 10mM or 0mM inorganic phosphate, to study the the transcription activation by Pho4 its cooperative binding factor Pho2, and its competitive binding factor Cbf1. (I) To infer how much Pho4 itself, Pho2 itself, and the interaction between Pho2 and Pho4 contribute to transcriptional activation in response to Pi starvation, we applied mutant cycle analysis to compare wild type, pho2Δ, pho4Δ and pho2Δ pho4Δ strains in both 10 mM and 0 mM Pi conditions. Mutant cycle analysis is a cyclic comparison among all various mutants. For example, by comparing pho2Δ and pho2Δ pho4Δ, we can directly infer the contribution from Pho4 alone to gene activation. And by comparing wild type and pho2Δ, we can infer the contribution from Pho2 alone together with that from the interaction between Pho2 and Pho4. (II) Compare two strains or one strain in two treatments in multiple replicates with dye-swap method. wt no vs high Pi, to identify genes that are induced in response to Pi starvation. cbf1Δ vs wt in high Pi, to identify the influence of Cbf1 on gene expression in high Pi condition. cbf1Δpho4Δ vs wt in high Pi, to identify the influence of Cbf1 on gene expression that is mediated through Pho4, in high Pi condition. rtg3Δtye7Δ vs wt in high Pi, to identify the influence of Rtg3 and Tye7 on gene expression in high Pi condition. pho80Δ vs pho80Δpho4Δ, to identify the genes that are activated Pho4 when Pho4 is fully nuclear localized. pho80Δcbf1Δ vs pho80Δcbf1Δpho4Δ, to identify the influence of Cbf1 on gene expression that is mediated through Pho4, when Pho4 is fully nuclear localized.

Project description:The budding yeast Saccharomyces cerevisiae alters its gene expression profile in response to a change in nutrient availability. The PHO-system is a well-studied case in the transcriptional regulation responding to nutritional changes in which a set of genes (PHO genes) is expressed to activate phosphate (Pi) metabolism for adaptation to Pi-starvation. Pi-starvation triggers an inhibition of Pho85 kinase, leading to migration of unphosphorylated Pho4 transcriptional activator into the nucleus enabling expression of PHO genes. When Pi is sufficient, the Pho85 kinase phosphorylates Pho4 thereby excluding it from the nucleus and resulting in repression (i.e., lack of transcription) of PHO genes. The Pho85 kinase has a role in various cellular functions other than regulation of the PHO system, in that Pho85 monitors whether environmental conditions are adequate for cell growth, and represses inadequate (untimely) responses in these cellular processes. In contrast, Pho4 appears to activate some genes involved in stress-response and is required for G1 arrest caused by DNA damage. These facts suggest the antagonistic function of these two players on a more general scale when yeast cells must cope with stress conditions. To explore general involvement of Pho4 in stress-response, we tried to identify Pho4-dependent genes by a genome-wide mapping of Pho4- and Rpo21-binding (Rpo21 being the largest subunit of RNA polymerase II) using a yeast tiling array. In the course of this study, we found Pi- and Pho4-regulated intragenic and antisense RNAs that could modulate the Pi-signal transduction pathway. Low-Pi signal is transmitted via certain inositol polyphosphate (IP) species (IP7) that are synthesized by Vip1 IP6 kinase. We have shown that Pho4 activates transcription of antisense and intragenic RNAs in the KCS1 locus to downregulate the Kcs1 activity, another IP6 kinase, by producing truncated Kcs1 protein via hybrid formation with the KCS1 mRNA and translation of the intragenic RNA, thereby enabling Vip1 to utilize more IP6 to synthesize IP7 functioning in low-Pi signaling. Since Kcs1 also can phosphorylate these IP7 species to synthesize IP8, reduction in the Kcs1 activity can ensure accumulation of the IP7 species, leading to further stimulation of low Pi-signaling, i.e., forming a positive feedback loop. We also report that genes apparently not involved in the PHO system are regulated by Pho4 either dependent upon or independently of the Pi conditions, and many of the latter genes are involved in stress-response. In S. cerevisiae, a large-scale cDNA analysis and mapping of RNA polymerase II binding using a high-resolution tiling array have identified a large number of antisense RNA species whose functions are yet to be clarified. Here we have shown that nutrient-regulated antisense and intragenic RNAs, as well as direct regulation of structural gene transcription, function in the response to nutrient availability. Our findings also imply that Pho4 is present in the nucleus even under high-Pi condition to activate or repress transcription, which challenges our current understanding of Pho4 regulation. Wild type and pho4 deletion mutant were grown in low or high phosphate medium and distribution of Rpo21 was analyzed.

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Komagataella phaffii encodes two Pho4 transcription factors: a comparative functional study under phosphate starvation and high pH stress

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