A measurable activation of the bZIP transcription factor Atf1 in a fission yeast strain devoid of stress-activated and cell integrity mitogen-activated protein kinase (MAPK) activities

CsAtf1, a bZIP transcription factor, is involved in fludioxonil sensitivity and virulence in the rubber tree anthracnose fungus Colletotrichum siamense

In phytopathogenic fungi, the HOG MAPK pathway has roles in osmoregulation, fungicide sensitivity, and other processes. The ATF1/CREB-activating transcription factor Atf1 is a regulator that functions downstream of the HOG MAPK pathway. Here, we identified a gene, designated CsAtf1, that encodes a bZIP transcription factor in Colletotrichum siamense, which is the main pathogen that causes Colletotrichum leaf fall disease in rubber trees in China. CsAtf1 localizes to the nucleus. Its mRNA expression correlates positively with that of CsPbs2 and CsHog1 in the HOG MAPK pathway in response to activator (anisomycin), inhibitor (SB203580) and fludioxonil treatments. The CsAtf1 deletion mutant showed slightly retarded mycelial growth, small conidia, slow spore germination, and abnormal appressorium formation. This mutant showed the increased spore germination rate after fludioxonil treatment and more resistance to the fungicide fludioxonil than did the wild-type fungus. However, unlike deletion of Pbs2 or Hog1, which resulted in greater sensitivity to osmotic stress, the CsAtf1 deletion induced slightly increased resistance to osmotic stress and the cell wall stress response. The ΔCsAtf1 strain also exhibited significantly reduced virulence on rubber tree leaves. These data revealed that CsAtf1 plays a key role in the regulation of fludioxonil sensitivity and in pathogenicity regulation in C. siamense.

Genes affecting the extension of chronological lifespan in Schizosaccharomyces pombe (fission yeast)

So far, more than 70 genes involved in the chronological lifespan (CLS) of Schizosaccharomyces pombe (fission yeast) have been reported. In this mini‐review, we arrange and summarize these genes based on the reported genetic interactions between them and the physical interactions between their products. We describe the signal transduction pathways that affect CLS in S. pombe: target of rapamycin complex 1, cAMP‐dependent protein kinase, Sty1, and Pmk1 pathways have important functions in the regulation of CLS extension. Furthermore, the Php transcription complex, Ecl1 family proteins, cyclin Clg1, and the cyclin‐dependent kinase Pef1 are important for the regulation of CLS extension in S. pombe. Most of the known genes involved in CLS extension are related to these pathways and genes. In this review, we focus on the individual genes regulating CLS extension in S. pombe and discuss the interactions among them.

Nitrogen starvation reveals the mitotic potential of mutants in the S/MAPK pathways

The genetics of quiescence is an emerging field compared to that of growth, yet both states generate spontaneous mutations and genetic diversity fueling evolution. Reconciling mutation rates in dividing conditions and mutation accumulation as a function of time in non-dividing situations remains a challenge. Nitrogen-starved fission yeast cells reversibly arrest proliferation, are metabolically active and highly resistant to a variety of stresses. Here, we show that mutations in stress- and mitogen-activated protein kinase (S/MAPK) signaling pathways are enriched in aging cultures. Targeted resequencing and competition experiments indicate that these mutants arise in the first month of quiescence and expand clonally during the second month at the expense of the parental population. Reconstitution experiments show that S/MAPK modules mediate the sacrifice of many cells for the benefit of some mutants. These findings suggest that non-dividing conditions promote genetic diversity to generate a social cellular environment prone to kin selection.

Nitrogen-starved fission yeast cells survive for weeks without dividing. Here, the authors show that some of these surviving cells accumulate mutations in the stress- and mitogen-activated protein kinase pathways and outcompete their parental cells, which provide nutrients for the mutant cells.

Antifungal compound honokiol triggers oxidative stress responsive signalling pathway and modulates central carbon metabolism

The fast growing evidences have shown that the plant-derived compound honokiol is a promising candidate for treating multiple human diseases, such as inflammation and cancer. However, the mode-of-action (MoA) of honokiol remains largely unclear. Here, we studied the antifungal activity of honokiol in fission yeast model, with the goal of understanding the honokiol's mechanism of action from the molecular level. We found that honokiol can inhibit the yeast growth at a dose-dependent way. Microarray analysis showed that honokiol has wide impacts on the fission yeast transcription levels (in total, 512 genes are up-regulated, and 42 genes are down-regulated). Gene set enrichment analysis indicated that over 45% up-regulated genes belong to the core environmental stress responses category. Moreover, network analysis suggested that there are extensive gene-gene interactions amongst the co-expression gene lists, which can assemble several biofunctionally important modules. It is noteworthy that several key components of central carbon metabolism, such as glucose transporters and metabolic enzymes of glycolysis, are involved in honokiol's MoA. The complexity of the honokiol's MoA displayed in previous studies and this work demonstrates that multiple omics approaches and bioinformatics tools should be applied together to achieve the complete scenario of honokiol's antifungal function.

Tor Signaling Regulates Transcription of Amino Acid Permeases through a GATA Transcription Factor Gaf1 in Fission Yeast

In the fission yeast, two Tor isoforms, Tor1 and Tor2, oppositely regulate gene expression of amino acid permeases. To elucidate the transcriptional machinery for these regulations, here we have employed the cap analysis of gene expression (CAGE), a method of analyzing expression profiles and identifying transcriptional start sites (TSSs). The loss of Tor1 decreased, and Tor2 inhibition by its temperature sensitive mutation increased, mRNA expression of isp5+, per1+, put4+ and SPBPB2B2.01. In contrast, the loss of Tor1 increased, and Tor2 inhibition decreased, the expression of cat1+. These changes were confirmed by semi-quantitative RT-PCR. These opposite effects by the loss of Tor1 and Tor2 inhibition appeared to occur evenly across multiple TSSs for the respective genes. The motif discovery analysis based on the CAGE results identified the GATA motifs as a potential cis-regulatory element for Tor-mediated regulation. In the luciferase reporter assay, the loss of Tor1 reduced, and Tor2 inhibition and nitrogen depletion increased, the activity of isp5+ promoter as well as that of a GATAAG reporter. One of the GATAAG motifs in isp5+ promoter was critical for its transcriptional activity, and a GATA transcription factor Gaf1 was critical for the activities of isp5+ promoter and the GATAAG reporter. Furthermore, Tor2 inhibition and nitrogen depletion induced nuclear localization of Gaf1 from the cytosol and its dephosphorylation. These results suggest that Tor2 inhibition, which is known to be induced by nitrogen depletion, promotes nuclear localization of Gaf1, thereby inducing isp5+ transcription through Gaf1 binding to the GATAAG motif in its promoter. Since Gaf1 was also critical for transcription of per1+ and put4+, Tor-Gaf1 signaling may coordinate transcription of multiple amino acid permeases according to nutrient availability.

Azoles activate Atf1-mediated transcription through MAP kinase pathway for antifungal effects in fission yeast

Azole antifungals directly inhibit enzymes for ergosterol biosynthesis, and this direct action is thought to underlie antifungal actions of these drugs. Recent studies showed that azoles alter expression of genes for various cellular functions. However, transcription factors regulated by azoles and their roles in antifungal actions remain poorly characterized. Using luciferase assay, we found that miconazole increased luciferase activity under the promoter containing the cAMP response element (CRE) motif. This azole-induced activation of CRE reporter was abolished in Atf1-deficient cells, suggesting that azoles induce Atf1 activation. As Atf1 is activated by stress-activated MAP kinase Sty1 upon various stressors, we examined its involvement. Azoles increased phosphorylation of Sty1 for its activation, and Sty1 deletion impaired azole-induced CRE reporter activation. In contrast, deletion of Pyp1, a tyrosine phosphatase which negatively regulates Sty1, increased CRE reporter activation. In addition, cells deficient in Atf1 and stress-activated MAP kinase pathway showed resistance to azoles, whereas cells lacking Pyp1 increased azole susceptibility, suggesting a critical role for azole-induced activation of MAP kinase-Atf1 pathway in antifungal actions of azoles. Collectively, these results suggest that azoles activate stress-activated MAP kinase pathway, thereby facilitating Atf1-mediated transcription for antifungal effects.

pREPORT: a multi-readout transcription reporter vector for fission yeast

Transcription factors are prominent regulators of gene expression that execute responses to various intracellular and extracellular stimuli. Recombinant transcription reporter systems can be conveniently used to study the DNA binding preferences and regulatory activity of a transcription factor under a range of conditions. Several reporter genes have been used to study transcription regulation in the fission yeast Schizosaccharomyces pombe. Each of these reporters has distinct advantages, such as high sensitivity or ease of use, and limitations, such as prohibitive costs or use of hazardous substances. To combine the strengths and mitigate the weaknesses of individual reporter genes, we have created pREPORT, a flexible multi-readout transcription reporter vector for fission yeast that employs an enhanced GFP-lacZ fusion and a customizable minimal promoter. With pREPORT, gene expression driven by the transcription factor of interest can be quantified in a number of ways, both in live cells and in vitro, using a single reporter construct.

FgSKN7 and FgATF1 have overlapping functions in ascosporogenesis, pathogenesis and stress responses in Fusarium graminearum

Fusarium head blight caused by Fusarium graminearum is one of the most destructive diseases of wheat and barley. Deoxynivalenol (DON) produced by the pathogen is an important mycotoxins and virulence factor. Because oxidative burst is a common defense response and reactive oxygen species (ROS) induces DON production, in this study, we characterized functional relationships of three stress-related transcription factor genes FgAP1, FgATF1 and FgSKN7. Although all of them played a role in tolerance to oxidative stress, deletion of FgAP1 or FgATF1 had no significant effect on DON production. In contrast, Fgskn7 mutants were reduced in DON production and defective in H2 O2 -induced TRI gene expression. The Fgap1 mutant had no detectable phenotype other than increased sensitivity to H2 O2 and Fgap1 Fgatf1 and Fgap1 Fgskn7 mutants lacked additional or more severe phenotypes than the single mutants. The Fgatf1, but not Fgskn7, mutant was significantly reduced in virulence and delayed in ascospore release. The Fgskn7 Fgatf1 double mutant had more severe defects in growth, conidiation and virulence than the Fgatf1 or Fgskn7 mutant. Instead of producing four-celled ascospores, it formed eight small, single-celled ascospores in each ascus. Therefore, FgSKN7 and FgATF1 must have overlapping functions in intracellular ROS signalling for growth, development and pathogenesis in F. graminearum.

Ecl1 is activated by the transcription factor Atf1 in response to H2O2 stress in Schizosaccharomyces pombe

The Ecl1 family genes extend the lifespan of fission yeast when overexpressed. They also cause resistance against H(2)O(2) stress. In this study, we found that the bZip transcription factor Atf1 is a direct activator of the induction of extender of chronological lifespan (ecl1 (+)) by H(2)O(2) stress. Based on ChIP analysis, we identified that Atf1 binds to the upstream DNA region of ecl1(+). Previously, we reported that overexpression of ecl1(+) increased the expression of the catalase-encoding ctt1(+). This ecl1(+)-dependent increase of ctt1(+) expression occurred in ∆atf1 mutant. On the other hand, the activation of ctt1 (+) caused by the ∆pyp1 mutation, which enhances Sty1-Atf1 activity, could occur in ∆ecl1 mutant. Based on these results, we propose that Atf1 can regulate ctt1(+) in both an Ecl1-dependent and an Ecl1-independent manner.

FTY720 stimulated ROS generation and the Sty1/Atf1 signaling pathway in the fission yeast Schizosaccharomyces pombe

Fingolimod hydrochloride (FTY720) is the first-in-class immune modulator known as sphingosine 1-phosphate (S1P) receptor agonists. FTY720 has also been reported to exert a variety of physiological functions such as antitumor effect, angiogenesis inhibition, and Ca2+ mobilization. Here, we show that FTY720 treatment induced reactive oxygen species (ROS) accumulation, and investigated the effect of FTY720 on the stress-activated MAP kinase Spc1/Sty1, a functional homologue of p38 MAPK, using a Renilla luciferase reporter construct fused to the CRE, which gives an accurate measure of the transcriptional activity of Atf1 and thus serves as a faithful readout of the Spc1/Sty1 MAPK signaling in response to oxidative stresses. FTY720 stimulated the CRE responses in a concentration-dependent manner, which was markedly reduced by deletion of the components of the Spc1/Sty1 MAPK pathway. The blockade of ROS production by NAC (N-acetyl-L-cysteine) significantly reversed the FTY720-induced ROS accumulation, subsequent activation of the Spc1/Sty1 MAPK pathway, and inhibition of cell proliferation. Cells lacking the components of the Spc1/Sty1 MAPK exhibited higher sensitivity to FTY720 and higher ROS levels upon FTY720 treatment than in wild-type cells. Thus, our results demonstrate the usefulness of fission yeast for elucidating the FTY720-mediated signaling pathways involving ROS.

Possible involvement of nitric oxide and reactive oxygen species in glucose deprivation-induced activation of transcription factor rst2

Glucose is one of the most important sources of cellular nutrition and glucose deprivation induces various cellular responses. In Schizosaccharomyces pombe, zinc finger protein Rst2 is activated upon glucose deprivation, and regulates gene expression via the STREP (stress response element of Schizosaccharomyces pombe) motif. However, the activation mechanism of Rst2 is not fully understood. We monitored Rst2 transcriptional activity in living cells using a Renilla luciferase reporter system. Hydrogen peroxide (H2O2) enhanced Rst2 transcriptional activity upon glucose deprivation and free radical scavenger inhibited Rst2 transcriptional activity upon glucose deprivation. In addition, deletion of the trx2 (+) gene encoding mitochondrial thioredoxin enhanced Rst2 transcriptional activity. Notably, nitric oxide (NO) generators enhanced Rst2 transcriptional activity upon glucose deprivation as well as under glucose-rich conditions. Furthermore, NO specific scavenger inhibited Rst2 transcriptional activity upon glucose deprivation. Altogether, our data suggest that NO and reactive oxygen species may be involved in the activation of transcription factor Rst2.

TORC1 signaling is governed by two negative regulators in fission yeast

The target of rapamycin (TOR) is a highly conserved protein kinase that regulates cell growth and metabolism. Here we performed a genome-wide screen to identify negative regulators of TOR complex 1 (TORC1) in Schizosaccharomyces pombe by isolating mutants that phenocopy Δtsc2, in which TORC1 signaling is known to be up-regulated. We discovered that Δnpr2 displayed similar phenotypes to Δtsc2 in terms of amino acid uptake defects and mislocalization of the Cat1 permease. However, Δnpr2 and Δtsc2 clearly showed different phenotypes in terms of rapamycin supersensitivity and Isp5 transcription upon various treatments. Furthermore, we showed that Tor2 controls amino acid homeostasis at the transcriptional and post-transcriptional levels. Our data reveal that both Npr2 and Tsc2 negatively regulate TORC1 signaling, and Npr2, but not Tsc2, may be involved in the feedback loop of a nutrient-sensing pathway.