Overexpression of UGT74E2, an Arabidopsis IBA Glycosyltransferase, Enhances Seed Germination and Modulates Stress Tolerance via ABA Signaling in Rice

Abstract

UDP-glycosyltransferases (UGTs) play key roles in modulating plant development and responses to environmental challenges. Previous research reported that the Arabidopsis UDP-glucosyltransferase 74E2 (<i>AtUGT74E2</i>), which transfers glucose to indole-3-butyric acid (IBA), is involved in regulating plant architecture and stress responses. Here, we show novel and distinct roles of <i>UGT74E2</i> in rice. We found that overexpression of <i>AtUGT74E2</i> in rice could enhance seed germination. This effect was also observed in the presence of IBA and abscisic acid (ABA), as well as salt and drought stresses. Further investigation indicated that the overexpression lines had lower levels of free IBA and ABA compared to wild-type plants. Auxin signaling pathway gene expression such as for <i>OsARF</i> and <i>OsGH3</i> genes, as well as ABA signaling pathway genes <i>OsABI3</i> and <i>OsABI5,</i> was substantially downregulated in germinating seeds of <i>UGT74E2</i> overexpression lines. Consistently, due to reduced IBA and ABA levels, the established seedlings were less tolerant to drought and salt stresses. The regulation of rice seed germination and stress tolerance could be attributed to IBA and ABA level alterations, as well as modulation of the auxin/ABA signaling pathways by <i>UGT74E2</i>. The distinct roles of <i>UGT74E2</i> in rice implied that complex and different molecular regulation networks exist between Arabidopsis and rice.