The yeast Saccharomycescerevisiae is capable of responding to various environmental stresses, such as salt stress. Such responses require a complex network and adjustment of the gene expression network. The goal of this study is to further understand the molecular mechanism of salt stress response in yeast, especially the molecular mechanism related to genes BDF1 and HAL2. The Bromodomain Factor 1 (Bdf1p) is a transcriptional regulator, which is part of the basal transcription factor TFIID. Cells lacking Bdf1p are salt sensitive with an abnormal mitochondrial function. We previously reported that the overexpression of HAL2 or deletion of HDA1 lowers the salt sensitivity of bdf1Δ. To better understand the mechanism behind the HAL2-related response to salt stress, we compared three global transcriptional profiles (bdf1Δ vs WT, bdf1Δ + HAL2 vs bdf1Δ, and bdf1Δhda1Δ vs bdf1Δ) in response to salt stress using DNA microarrays. Our results reveal that genes for iron acquisition and cellular and mitochondrial remodeling are induced by HAL2. Overexpression of HAL2 decreases the concentration of nitric oxide. Mitochondrial iron–sulfur cluster (ISC) assembly also decreases in bdf1Δ + HAL2. These changes are similar to the changes of transcriptional profiles induced by iron starvation. Taken together, our data suggest that mitochondrial functions and iron homeostasis play an important role in bdf1Δ-induced salt sensitivity and salt stress response in yeast.

Bromodomain-containing transcription factor, a kind of important regulating protein, can recognize and bind to acetylated histone. The homologous genes, BDF1 and BDF2, in Saccharomyces cerevisiae, respectively, encode a bromodomain-containing transcription factor. Previously study has demonstrated that both BDF1 and BDF2 participate in yeast salt stress response. Bdf1p deletion cells are sensitive to salt stress and this phenotype is suppressed by its homologue BDF2 in a dosage-dependent manner. In this study, we show that the histone deacetylase SIR2 over-expression enhanced dosage-dependent compensation of BDF2. SIR2 over-expression induced a global transcription change, and 1959 gene was down-regulated. We deleted some of the most significant down-regulated genes and did the spot assay. The results revealed that LSP1, an upstream component of endocytosis pathway, and CIN5, a transcription factor that mediates cellular resistance to stresses, can enhance salt resistance of bdf1∆. Further analysis demonstrated that under salt stress the endocytosis is over-activated in bdf1∆ but was recovered in bdf1∆lsp1∆. To our best knowledge, this is the first report that the transcription factor Bdf1p regulates endocytosis under salt stress via LSP1, a major component of eisosomes that regulate the sites of endocytosis.

The phenolic compounds present in hydrolysates pose significant challenges for the sustainable lignocellulosic materials refining industry. Three Saccharomyces cerevisiae strains with high tolerance to lignocellulose hydrolysate were obtained through ethyl methanesulfonate mutation and adaptive evolution. Among them, strain EMV-8 exhibits specific tolerance to vanillin, a phenolic compound common in lignocellulose hydrolysate. The EMV-8 maintains a specific growth rate of 0.104 h−1 in 2 g L−1 vanillin, whereas the reference strain cannot grow. Physiological studies revealed that the vanillin reduction rate of EMV-8 is 1.92-fold higher than its parent strain, and the Trolox equivalent antioxidant capacity of EMV-8 is 15 % higher than its parent strain. Transcriptional analysis results confirmed an up-regulated oxidoreductase activity and antioxidant activity in this strain. Our results suggest that enhancing the antioxidant capacity and oxidoreductase activity could be a strategy to engineer S. cerevisiae for improved vanillin tolerance.

Chitosanases are lytic enzymes involved in the degradation of chitosan, a component of fungal cell walls. The phytopathogenic fungus Fusarium solani produces an extracellular chitosanase, CSN1, the role of which in the physiology and virulence of the fungus remains to be expounded. Here, we studied the expression of the CSN1 gene through gene silencing and examined its effect on fungal pathogenicity. A vector construct encoding a hairpin RNA (hpRNA) of CSN1 was constructed and introduced into the F. solani 0114 strain. The results revealed that majority of the transformants exhibited a significant reduction in chitosanase activity compared with the wild-type strain. Further, transformants with silenced CSN1 exhibited no change in mycelial growth and spore formation. However, pea pod and seedling bioassays indicated that transformants with silenced CSN1 were more virulent compared with the wild-type strain, and in sharp contrast to strains in which overexpression of the CSN1 gene resulted in virulence reduction. Although the mechanism remains unclear, our findings did suggest that F. solani chitosanase has a negative effect on fungal pathogenicity.

To overexpress the chitosanase gene (csn) in F. solani, a vector based on pCAMBIA 1300 was constructed. The csn gene, which is under control of the Aspergillus nidulansgpdA promoter and A. nidulans trpC terminator, was introduced back into the F. solani genome by Agrobacterium tumefaciens-mediated transformation, and the herbicide-resistance gene bar from Streptomyces hygroscopicus was used as the selection marker. Transformants which showed a significant increase in chitosanase production (~2.1-fold than control) were obtained. Southern blot analysis indicated that most transformants had a single-copy T-DNA integration.

The Saccharomyces cerevisiae BDF1 gene, which encodes a bromodomain-containing transcription factor, was previously isolated by transposon mutugenesis in a screen for salt-sensitive mutants. However, the salt stress response mechanism regulated by bromodomain transcription factor 1 protein (Bdf1p) remains poorly understood. In this report, genetic analysis indicated that the salt sensitivity of the BDF1 deletion mutant was suppressed by increased gene dosage of its homologous gene BDF2. Furthermore, comparative transcriptome analysis revealed that the differences in transcriptional response between the wild type and the bdf1Δ mutant in the presence of salt stress (0.6 mol/L NaCl, 45 min) were mainly related to cell-wall biosynthesis, the mitochondria, and several unknown genes. Our results provided further information about the regulatory mechanism involved in the salt stress response and adds new insight for understanding the biological functional of bromdomain-containing proteins in cellular processes.

•Xylose isomerases genes were screened for efficient expression in Saccharomyces cerevisiae.•The xylose isomerase from bovine rumen exhibited high activity when expressing in S. cerevisiae.•A variant containing two mutations (K11T/D220V) of Ru-XI that exhibited 68% increase in enzyme activity was isolated.The conversion of abundant levels of xylose in lignocellulosic materials into viable products would generate economic benefits. The heterologous expression of the xylose isomerase (XI) gene is considered a direct and effective strategy for establishing the xylose metabolic pathway in Saccharomyces cerevisiae. However, only limited sources of xylA are functionally expressed in S. cerevisiae and are capable of driving effective xylose consumption. In this study, Ru-xylA (where Ru represents the rumen), which was screened from the contents of the bovine rumen metagenomic library, was functionally expressed in S. cerevisiae, and the enzyme activity was 1.31 U mg−1 protein. This is a new source of XI that can exhibit high activity levels in S. cerevisiae. The activity of this enzyme is comparable to those of the Piromyces sp. XI. Then, the Ru-XI activity was further improved through mutagenesis and growth-based screening in a centromeric plasmid. A variant containing two mutations (K11T/D220V) that exhibited a 68% increase in enzyme activity was isolated. Our work identified a new xylose isomerase that can be functionally expressed in S. cerevisiae and results in a higher XI enzyme activity through mutagenesis.