Rice glycosyltransferase DUGT2 enhances drought and salt tolerances through glycosylating a broad-spectrum of flavonoids under bZIP16 regulation.

UDP-glycosyltransferase (UGT) constitute a superfamily and get dramatic expansion during evolution of land plants. However, their biological significances in stress responses are largely unclear. In addition, it is well known that accumulation of flavonoids enable plants to cope with stressful environments, but the molecular mechanism underlying metabolism regulation of flavonoids under stress conditions remains unanswered. Here, we analyzed the impact of a rice UGT gene, DUGT2, on flavonoid metabolism under stress conditions by using genetic, biochemical, molecular, and omics methods. We found that overexpression of DUGT2 enhanced plant tolerance to drought and salt, while DUGT2 knockout mutants showed a more sensitive phenotype. Our metabolomics analysis showed that the mutants had the most significant reduction in flavonoids under stress conditions compared to the wild type. Subsequent biochemical analysis verified a broad-spectrum enzyme activity of DUGT2 toward flavonoids, suggesting that DUGT2 can affect flavonoid metabolism by flavonoid glycosylation. Furthermore, our transcriptome analysis revealed that the loss of DUGT2 function led to a significant decrease in the expression of genes related to flavonoid biosynthesis and antioxidant enzymes, which might be achieved through feedback regulation. Moreover, we identified an upstream regulator, bZIP16, and demonstrated its positive regulation on DUGT2 transcription activity. Overall, this work reveals that DUGT2 could enhance abiotic stress tolerance by the glycosylation-promoted flavonoid metabolism under the regulation of bZIP16. This work can not only help to understand the biological functions of UGT superfamily in stress responses, but also get a new insight into the regulation mechanism of flavonoid metabolism, especially under stress conditions.