Systematic analysis of the Diacylglycerol acyltransferase (DGAT) genes in oat and functional characterazation of AsDGAT2-1 involved in oil accumulation and cold stress tolerance

Diacylglycerol acyltransferase (DGAT) catalyzes the final committed step in triacylglycerol (TAG) biosynthesis and is a key determinant of seed oil content and fatty acid (FA) composition. Although oat (Avena sativa L.) possesses the highest seed oil content among cereals, the functions of its DGAT gene family remain poorly understood. Here, we identified 12 AsDGAT genes in the oat genome and systematically analyzed their sequence features, gene structures, and phylogenetic relationships. Promoter analysis revealed that AsDGAT genes contain multiple cis-regulatory elements associated with light, phytohormones, metabolism, and stress responses, suggesting roles in development and stress adaptation. Expression profiling showed that AsDGAT genes display distinct tissue-specific patterns and respond differentially to hormone and abiotic stress treatments. Notably, AsDGAT2-1 was predominantly expressed in developing seeds. Heterologous expression in a TAG-deficient yeast mutant confirmed its in vivo DGAT activity, and subcellular localization showed that AsDGAT2-1 was located at the endoplasmic reticulum, the primary site of TAG assembly. Overexpression of AsDGAT2-1 in tobacco significantly increased total seed oil content and shifted FA composition toward elevated oleic acid accumulation. Transgenic tobacco plants also exhibited enhanced cold tolerance. Our work provides a comprehensive characterization of the DGAT family in oat and identifies AsDGAT2-1 as a promising dual-function candidate for engineering high-oleic-acid oil production and improved cold resilience in plants.