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1. Independent Mechanisms for Acquired Salt Tolerance versus Growth Resumption Induced by Mild Ethanol Pretreatment in Saccharomyces cerevisiae

   https://doi.org/10.1128/mSphere.00574-18  

   McDaniel, Elizabeth A. ; Stuecker, Tara N. ; Veluvolu, Manasa ; Gasch, Audrey P. ; Lewis, Jeffrey A. ; Mitchell, Aaron P. ( December 2018 , mSphere)

   ABSTRACT All living organisms must recognize and respond to various environmental stresses throughout their lifetime. In natural environments, cells frequently encounter fluctuating concentrations of different stressors that can occur in combination or sequentially. Thus, the ability to anticipate an impending stress is likely ecologically relevant. One possible mechanism for anticipating future stress is acquired stress resistance, where cells preexposed to a mild sublethal dose of stress gain the ability to survive an otherwise lethal dose of stress. We have been leveraging wild strains of Saccharomyces cerevisiae to investigate natural variation in the yeast ethanol stress response and its role in acquired stress resistance. Here, we report that a wild vineyard isolate possesses ethanol-induced cross protection against severe concentrations of salt. Because this phenotype correlates with ethanol-dependent induction of the ENA genes, which encode sodium efflux pumps already associated with salt resistance, we hypothesized that variation in ENA expression was responsible for differences in acquired salt tolerance across strains. Surprisingly, we found that the ENA genes were completely dispensable for ethanol-induced survival of high salt concentrations in the wild vineyard strain. Instead, the ENA genes were necessary for the ability to resume growth on high concentrations of salt following a mildmore »ethanol pretreatment. Surprisingly, this growth acclimation phenotype was also shared by the lab yeast strain despite lack of ENA induction under this condition. This study underscores that cross protection can affect both viability and growth through distinct mechanisms, both of which likely confer fitness effects that are ecologically relevant. IMPORTANCE Microbes in nature frequently experience “boom or bust” cycles of environmental stress. Thus, microbes that can anticipate the onset of stress would have an advantage. One way that microbes anticipate future stress is through acquired stress resistance, where cells exposed to a mild dose of one stress gain the ability to survive an otherwise lethal dose of a subsequent stress. In the budding yeast Saccharomyces cerevisiae , certain stressors can cross protect against high salt concentrations, though the mechanisms governing this acquired stress resistance are not well understood. In this study, we took advantage of wild yeast strains to understand the mechanism underlying ethanol-induced cross protection against high salt concentrations. We found that mild ethanol stress allows cells to resume growth on high salt, which involves a novel role for a well-studied salt transporter. Overall, this discovery highlights how leveraging natural variation can provide new insights into well-studied stress defense mechanisms.« less
2. Tup1 Paralog CgTUP11 Is a Stronger Repressor of Transcription than CgTUP1 in Candida glabrata

   https://doi.org/10.1128/msphere.00765-21  

   Bui, Lilian N. ; Iosue, Christine L. ; Wykoff, Dennis D. ( April 2022 , mSphere)

   Mitchell, Aaron P. (Ed.)

   ABSTRACT TUP1 is a well-characterized repressor of transcription in Saccharomyces cerevisiae and Candida albicans and is observed as a single-copy gene. We observe that most species that experienced a whole-genome duplication outside of the Saccharomyces genus have two copies of TUP1 in the Saccharomycotina yeast clade. We focused on Candida glabrata and demonstrated that the uncharacterized TUP1 homolog, C. glabrata TUP11 ( CgTUP11 ), is most like the S. cerevisiae TUP1 ( ScTUP1 ) gene through phenotypic assays and transcriptome sequencing (RNA-seq). Whereas CgTUP1 plays a role in gene repression, it is much less repressive in standard growth media. Through RNA-seq and reverse transcription-quantitative PCR (RT-qPCR), we observed that genes associated with pathogenicity ( YPS2 , YPS4 , and HBN1 ) are upregulated upon deletion of either paralog, and loss of both paralogs is synergistic. Loss of the corepressor CgCYC8 mimics the loss of both paralogs, but not to the same extent as the Cgtup1 Δ Cgtup11 Δ mutant for these pathogenesis-related genes. In contrast, genes involved in energy metabolism ( CgHXT2 , CgADY2 , and CgFBP1 ) exhibit similar behavior (dependence on both paralogs), but deletion of CgCYC8 is very similar to the Cgtup1 Δ Cgtup11 Δ mutant. Finally,more »some genes ( CgMFG1 and CgRIE1 ) appear to only be dependent on CgTUP11 and CgCYC8 and not CgTUP1 . These data indicate separable and overlapping roles for the two TUP1 paralogs and that other genes may function as the Cg Cyc8 corepressor. Through a comparison by RNA-seq of Sctup1 Δ, it was found that TUP1 homologs regulate similar genes in the two species. This work highlights that studies focused only on Saccharomyces may miss important biological processes because of paralog loss after genome duplication. IMPORTANCE Due to a whole-genome duplication, many yeast species related to C. glabrata have two copies of the well-characterized TUP1 gene, unlike most Saccharomyces species. This work identifies roles for the paralogs in C. glabrata , highlights the importance of the uncharacterized paralog, called TUP11 , and suggests that the two paralogs have both overlapping and unique functions. The TUP1 paralogs likely influence pathogenicity based on tup mutants upregulating genes that are associated with pathogenicity.« less
3. Physiological and Multi-Omics Approaches for Explaining Drought Stress Tolerance and Supporting Sustainable Production of Rice

   https://doi.org/10.3389/fpls.2021.803603  

   Zargar, Sajad Majeed ; Mir, Rakeeb Ahmad ; Ebinezer, Leonard Barnabas ; Masi, Antonio ; Hami, Ammarah ; Manzoor, Madhiya ; Salgotra, Romesh K. ; Sofi, Najeebul Rehman ; Mushtaq, Roohi ; Rohila, Jai Singh ; et al ( January 2022 , Frontiers in Plant Science)

   Drought differs from other natural disasters in several respects, largely because of the complexity of a crop’s response to it and also because we have the least understanding of a crop’s inductive mechanism for addressing drought tolerance among all abiotic stressors. Overall, the growth and productivity of crops at a global level is now thought to be an issue that is more severe and arises more frequently due to climatic change-induced drought stress. Among the major crops, rice is a frontline staple cereal crop of the developing world and is critical to sustaining populations on a daily basis. Worldwide, studies have reported a reduction in rice productivity over the years as a consequence of drought. Plants are evolutionarily primed to withstand a substantial number of environmental cues by undergoing a wide range of changes at the molecular level, involving gene, protein and metabolite interactions to protect the growing plant. Currently, an in-depth, precise and systemic understanding of fundamental biological and cellular mechanisms activated by crop plants during stress is accomplished by an umbrella of -omics technologies, such as transcriptomics, metabolomics and proteomics. This combination of multi-omics approaches provides a comprehensive understanding of cellular dynamics during drought or other stress conditionsmore »in comparison to a single -omics approach. Thus a greater need to utilize information (big-omics data) from various molecular pathways to develop drought-resilient crop varieties for cultivation in ever-changing climatic conditions. This review article is focused on assembling current peer-reviewed published knowledge on the use of multi-omics approaches toward expediting the development of drought-tolerant rice plants for sustainable rice production and realizing global food security.« less
4. A Novel cis Element Achieves the Same Solution as an Ancestral cis Element During Thiamine Starvation in Candida glabrata

   https://doi.org/10.1534/g3.119.400897  

   Iosue, Christine L. ; Gulotta, Anthony P. ; Selhorst, Kathleen B. ; Mody, Alison C. ; Barbour, Kristin M. ; Marcotte, Meredith J. ; Bui, Lilian N. ; Leone, Sarah G. ; Lang, Emma C. ; Hughes, Genevieve H. ; et al ( January 2020 , G3: Genes|Genomes|Genetics)

   Regulatory networks often converge on very similar cis sequences to drive transcriptional programs due to constraints on what transcription factors are present. To determine the role of constraint loss on cis element evolution, we examined the recent appearance of a thiamine starvation regulated promoter in Candida glabrata . This species lacks the ancestral transcription factor Thi2, but still has the transcription factor Pdc2, which regulates thiamine starvation genes, allowing us to determine the effect of constraint change on a new promoter. We identified two different cis elements in C. glabrata - one present in the evolutionarily recent gene called CgPMU3 , and the other element present in the other thiamine (THI) regulated genes. Reciprocal swaps of the cis elements and incorporation of the S. cerevisiae Thi2 transcription factor-binding site into these promoters demonstrate that the two elements are functionally different from one another. Thus, this loss of an imposed constraint on promoter function has generated a novel cis sequence, suggesting that loss of trans constraints can generate a non-convergent pathway with the same output.
5. Regulation of biotic interactions and responses to abiotic stresses by MAP kinase pathways in plant pathogenic fungi

   https://doi.org/10.1007/s44154-021-00004-3  

   Zhang, Xue ; Wang, Zeyi ; Jiang, Cong ; Xu, Jin-Rong ( December 2021 , Stress Biology)

   Abstract Like other eukaryotes, fungi use MAP kinase (MAPK) pathways to mediate cellular changes responding to external stimuli. In the past two decades, three well-conserved MAP kinase pathways have been characterized in various plant pathogenic fungi for regulating responses and adaptations to a variety of biotic and abiotic stresses encountered during plant infection or survival in nature. The invasive growth (IG) pathway is homologous to the yeast pheromone response and filamentation pathways. In plant pathogens, the IG pathway often is essential for pathogenesis by regulating infection-related morphogenesis, such as appressorium formation, penetration, and invasive growth. The cell wall integrity (CWI) pathway also is important for plant infection although the infection processes it regulates vary among fungal pathogens. Besides its universal function in cell wall integrity, it often plays a minor role in responses to oxidative and cell wall stresses. Both the IG and CWI pathways are involved in regulating known virulence factors as well as effector genes during plant infection and mediating defenses against mycoviruses, bacteria, and other fungi. In contrast, the high osmolarity growth (HOG) pathway is dispensable for virulence in some fungi although it is essential for plant infection in others. It regulates osmoregulation in hyphae and ismore »dispensable for appressorium turgor generation. The HOG pathway also plays a major role for responding to oxidative, heat, and other environmental stresses and is overstimulated by phenylpyrrole fungicides. Moreover, these three MAPK pathways crosstalk and coordinately regulate responses to various biotic and abiotic stresses. The IG and CWI pathways, particularly the latter, also are involved in responding to abiotic stresses to various degrees in different fungal pathogens, and the HOG pathway also plays a role in interactions with other microbes or fungi. Furthermore, some infection processes or stress responses are co-regulated by MAPK pathways with cAMP or Ca 2+ /CaM signaling. Overall, functions of individual MAP kinase pathways in pathogenesis and stress responses have been well characterized in a number of fungal pathogens, showing the conserved genetic elements with diverged functions, likely by rewiring transcriptional regulatory networks. In the near future, applications of genomics and proteomics approaches will likely lead to better understanding of crosstalk among the MAPKs and with other signaling pathways as well as roles of MAPKs in defense against other microbes (biotic interactions).« less