Overexpression of a Common Wheat Gene GALACTINOL SYNTHASE3 Enhances Tolerance to Zinc in Arabidopsis and Rice Through the Modulation of Reactive Oxygen Species Production

Galactinol synthase (GolS, EC 2.4.1.123), a key enzyme in the biosynthesis of raffinose family oligosaccharides (RFOs), plays roles in plant growth and developmental processes. The in vitro roles of GolS in plant responses against heavy metal stress are not well clarified. In the present study, a suppression-subtractive hybridization (SSH) cDNA library has been constructed using RNA extracted from wheat cultivar Jinan 18 treated with ZnCl2 as the tester and RNA from untreated seedlings as the driver. Sixteen expressed sequence tags (ESTs) highly homologous with known proteins associated with stress tolerance have been obtained. Among these, a 1000-bp cDNA sequence encoding GolS protein has been isolated and designated as TaGolS3. Real-time quantitative PCR (qPCR) analysis revealed that TaGolS3 was mainly expressed in young roots and upregulated by exogenous ABA treatment and several abiotic stresses, such as ZnCl2, CuCl2, low temperature, and NaCl. Subcellular localization analysis showed that TaGolS3 protein is a nuclear-localized protein. A detailed analysis of Arabidopsis and rice transgenic plants overexpressing TaGolS3 gene displayed that transgenic plants exhibited increased lateral root number, primary root length, plant survival rate, and plant height. Moreover, in comparison with the wild-type (WT) plants, the TaGolS3-overexpressing lines showed a higher expression of ROS-scavenging genes, activities of antioxidative enzymes, proline contents, and a lower level of malondialdehyde (MDA) contents and electrolyte leakage under zinc stress. These results confirmed the positive roles of TaGolS3 in improving plant tolerance to heavy metal stress, indicating a potential resource in the transgenic breeding to enhance heavy metal stress tolerance in crop plants.