Search

The understanding of the molecular mechanisms underlying acquired herbicide resistance is crucial in dealing with the emergence of resistant weeds. Saccharomyces cerevisiae has been used as a model system to gain insights into the mechanisms underlying resistance to the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The TPO1 gene, encoding a multidrug resistance (MDR) plasma membrane transporter of the major facilitator superfamily (MFS), was previously found to confer resistance to 2,4-D in yeast and to be transcriptionally activated in response to the herbicide. In this work, we demonstrate that Tpo1p is required to reduce the intracellular concentration of 2,4-D. ScTpo1p homologs encoding putative plasma membrane MFS transporters from the plant model Arabidopsis thaliana were analyzed for a possible role in 2,4-D resistance. At5g13750 was chosen for further analysis, as its transcript levels were found to increase in 2,4-D stressed plants. The functional heterologous expression of this plant open reading frame in yeast was found to confer increased resistance to the herbicide in Δtpo1 and wild-type cells, through the reduction of the intracellular concentration of 2,4-D. Heterologous expression of At5g13750 in yeast also leads to increased resistance to indole-3-acetic acid (IAA), Al3+ and Tl3+. At5g13750 is the first plant putative MFS transporter to be suggested as possibly involved in MDR. [ABSTRACT FROM AUTHOR]

The understanding of the molecular basis of yeast resistance to ethanol may guide the design of rational strategies to increase process performance in industrial alcoholic fermentations. In this study, the yeast disruptome was screened for mutants with differential susceptibility to stress induced by high ethanol concentrations in minimal growth medium. Over 250 determinants of resistance to ethanol were identified. The most significant gene ontology terms enriched in this data set are those associated with intracellular organization, biogenesis, and transport, in particular, regarding the vacuole, the peroxisome, the endosome, and the cytoskeleton, and those associated with the transcriptional machinery. Clustering the proteins encoded by the identified determinants of ethanol resistance by their known physical and genetic interactions highlighted the importance of the vacuolar protein sorting machinery, the vacuolar H+-ATPase complex, and the peroxisome protein import machinery. Evidence showing that vacuolar acidification and increased resistance to the cell wall lytic enzyme β-glucanase occur in response to ethanol-induced stress was obtained. Based on the genome-wide results, the particular role of the FPS1 gene, encoding a plasma membrane aquaglyceroporin which mediates controlled glycerol efflux, in ethanol stress resistance was further investigated. FPSI expression contributes to decreased [3H]ethanol accumulation in yeast cells, suggesting that Fps1p may also play a role in maintaining the intracellular ethanol level during active fermentation. The increased expression of FPS1 confirmed the important role of this gene in alcoholic fermentation, leading to increased final ethanol concentration under conditions that lead to high ethanol production. [ABSTRACT FROM AUTHOR]

Abstract: Yeast cells adapted to the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) exhibit a plasma membrane less susceptible to 2,4-D-induced disruption and are more tolerant than unadapted cells to lethal concentrations of the herbicide. These cells, adapted to grow in the presence of increasing concentrations of 2,4-D, were found to exhibit a dose-dependent increase of the saturation degree of membrane fatty acids, associated to the higher percentage of stearic (C18:0) and palmitic (C16:0) acids, and to the decreased percentage of palmitoleic (Δ9-cisC16:1) and oleic (Δ9-cisC18:1) acids. The decreased transcription of the OLE1 gene (encoding the Δ9 fatty acid desaturase that catalyses the conversion of palmitic and stearic acids to palmitoleic and oleic acids, respectively) registered in 2,4-D adapted cells suggests that yeast adaptation to the herbicide involves the enhancement of the ratio of saturated (C16:0 and C18:0) to monounsaturated (C16:1 and C18:1) membrane fatty acids through a reduced OLE1 expression. [Copyright &y& Elsevier]