The UDP-dependent glycosyltransferase MdUGT88F4 of apple (Malus domestica) functions in drought tolerance by promoting the accumulation of isosalipurposide and amino acids

Abstract Members of the UDP-dependent glycosyltransferase (UGT) family play critical roles in plant stress responses. MdUGT88F4 , a key UDP-glucose: phloretin 2’-O-glucosyltransferase gene in Malus spp., was previously identified to catalyze the biosynthesis of the dihydrochalcone compound isosalipurposide, but its role in abiotic stress tolerance remains unexplored. In this study MdUGT88F4 expression was found to be upregulated by drought stress . Overexpression of MdUGT88F4 alleviated drought-induced growth inhibition of transgenic apple plants. Under drought conditions, transgenic lines overexpressing MdUGT88F4 (OX) exhibited reduced leaf wilting, along with significantly lower relative electrolyte leakage and malondialdehyde content compared to wild type (WT). Conversely, OX plants showed higher relative water content and total chlorophyll levels. Notably, OX plants displayed enhanced photosynthetic capacity and reduced reactive oxygen species (ROS) accumulation under drought conditions. Drought stress induced isosalipurposide accumulation in apple plants, with OX plants showing significantly higher levels than WT. Furthermore, most amino acids and their derivatives were detected at higher concentrations in the OX plants, which also exhibited enhanced accumulation of amino acids under drought conditions, implying presence of a more robust metabolic adjustment. RNA-seq analysis revealed that differences in metabolic processes, particularly amino acid metabolism, contributed to the enhanced drought tolerance in the OX plants. Collectively, these findings indicate that MdUGT88F4 positively modulates drought tolerance in apple by promoting isosalipurposide synthesis and coordinating amino acid metabolism.