The transcription factor GCN4 regulates PHM8 and alters triacylglycerol metabolism in Saccharomyces cerevisiae

The role of yeast m6A methyltransferase in peroxisomal fatty acid oxidation

The precise and controlled regulation of gene expression at transcriptional and post-transcriptional levels is crucial for the eukaryotic cell survival and functions. In eukaryotes, more than 100 types of post-transcriptional RNA modifications have been identified. The N⁶-methyladenosine (m⁶A) modification in mRNA is among the most common post-transcriptional RNA modifications known in eukaryotic organisms, and the m⁶A RNA modification can regulate gene expression. The role of yeast m⁶A methyltransferase (Ime4) in meiosis, sporulation, triacylglycerol metabolism, vacuolar morphology, and mitochondrial functions has been reported. Stress triggers triacylglycerol accumulation as lipid droplets. Lipid droplets are physically connected to the different organelles such as endoplasmic reticulum, mitochondria, and peroxisomes. However, the physiological relevance of these physical interactions remains poorly understood. In yeast, peroxisome is the sole site of fatty acid β-oxidation. The metabolic status of the cell readily governs the number and physiological function of peroxisomes. Under low-glucose or stationary-phase conditions, peroxisome biogenesis and proliferation increase in the cells. Therefore, we hypothesized a possible role of Ime4 in the peroxisomal functions. There is no report on the role of Ime4 in peroxisomal biology. Here, we report that IME4 gene deletion causes peroxisomal dysfunction under stationary-phase conditions in Saccharomyces cerevisiae; besides, the ime4Δ cells showed a significant decrease in the expression of the key genes involved in peroxisomal β-oxidation compared to the wild-type cells. Therefore, identification and determination of the target genes of Ime4 that are directly involved in the peroxisomal biogenesis, morphology, and functions will pave the way to better understand the role of m⁶A methylation in peroxisomal biology.

Functional analysis of diacylglycerol O-acyl transferase 2 gene to decipher its role in virulence of Botrytis cinerea

Gray mold disease inflicted by Botrytis cinerea is a serious menace responsible for significant economic loss worldwide. Due to its polyphagous nature, the pathogen has enthused inquisitiveness in researchers to unravel its complexity. Agrobacterium tumefaciens-mediated transformation was used to generate insertional mutants of Botrytis cinerea. A mutant (BCM-55) with disruption in a gene (BcDGAT2) that encodes for diacylglycerol O-acyl transferase 2 (DGAT2), showed enervated virulence on various hosts' tissues. Enzyme DGAT2 is crucial in the final step of synthesis of triacylglycerol (TAG) that plays an important role in homeostasis of membrane and cellular processes. However, the role of DGAT2 has never been reported in a phytopathogenic fungus. In this study, BCM-55 was characterized to ascertain the role of DGAT2 in virulence of B. cinerea. The insertional mutant was defective in spore production and lacked sclerotia formation as a consequence of lower accumulation of TAG. A significant delay in spore germination in BCM-55 was accompanied with a low penetration potential. Hyphae of the mutant formed swollen endings with considerable impairment in penetration. Deletion of BcDGAT2 also led to increased sensitivity towards cell wall and membrane-disturbing agents. Furthermore, BCM-55 was deficient in the production of oxalic acid and showed lower activity of a cell wall-degrading enzyme, polygalacturonase. The role of BcDGAT2 in virulence was further confirmed by targeted deletion and complementation of the gene. The results insinuate a crucial role of BcDGAT2 in penetration and consequently virulence of B. cinerea. The study provides novel insights into plant-pathogen interactions that can be exploited to develop suitable disease management strategies.

Yeast ENV9 encodes a conserved lipid droplet (LD) short-chain dehydrogenase involved in LD morphology

Lipid droplets (LDs) have emerged as dynamic and interactive organelles with important roles in lipid metabolism and membrane biogenesis. Here, we report that Saccharomyces cerevisiae Env9 is a novel conserved oxidoreductase involved in LD morphology. Microscopic and biochemical studies confirm localization of tagged Env9 to LDs and implicate its C-terminal hydrophobic domain (aa241-265) in its membrane association and stability. Confocal studies reveal a role for Env9 in LD morphology. Env9 positively affects both formation of large LDs upon overexpression and LD proliferation under poor carbon source. In silico bioinformatic and modeling approaches establish that ENV9 is a widely conserved member of the short-chain dehydrogenase (SDR) superfamily. Bayesian phylogenetic studies strongly support ENV9 as an ortholog of human SDR retinol dehydrogenase 12 (RDH12). Dehydrogenase activity of Env9 was confirmed by in vitro oxidoreductase assays. RDH12 mutations have been linked to Leber Congenital Amaurosis. Similar site-directed point mutations in the predicted Env9 oxidoreductase active site (N146L) or cofactor-binding site (G23-24A) abolished its reductase activity in vitro, consistent with those reported in other retinol dehydrogenases. The same residues were essential for affecting LD size and number in vivo. Taken together, our results implicate oxidoreductase activity of Env9 in its cellular role in LD morphology.