Antisense suppression of cucumber (Cucumis sativus L.) sucrose synthase 3 (CsSUS3) reduces hypoxic stress tolerance

Abstract

Sucrose synthase (SUS; EC 2.4.1.13) plays important roles in sugar metabolism and abiotic stress response. But the genes encoding SUS in cucumber (Cucumis sativusL.) have not been well studied. Here, we isolated four cucumber sucrose synthase genes (CsSUS). Among them, CsSUS3, which highly expressed in the roots, was chosen for further study. Immunolocalization and subcellular localization analysis indicated that CsSUS3 localized in the cytosol and the plasma membrane, and mainly existed in the companion cells of phloem in the roots. When suffering hypoxia stress from flooding, CsSUS3 expression and SUS activity in roots increased, especially in the lateral roots; moreover, the soluble SUS activity increased clearly, but the membrane fraction hardly changed. Compared with the wild-type cucumbers, the transgenic lines with antisense expression of CsSUS3 were more sensitive to flooding. After 6 d of flooding, the SUS activity, soluble sugar and uridine 5′-diphosphate glucose (UDPG) content and the ratio of ATP/ADP in the roots of transgenic plants were significantly lower than that in wild-type plants. Moreover, the transgenic lines grew more slowly with more yellow necrosis in the leaves. These findings suggested CsSUS3 participated in resisting hypoxic stress. Furthermore, the mechanism of CsSUS3 in resisting hypoxic stress was also discussed. Cucumber is an important horticultural crop, but it often suffers from the heavy rainstorm which led excessive accumulation of water in field so affected the growth in summer growing season. It has been reported that sucrose synthase (SUS; EC 2.4.1.13) was a low oxygen induced protein, but the role and functional mechanism of SUS in low oxygen conditions is controversial. In this study, four putative CsSUS cDNA were first isolated from cucumber. Among these genes, CsSUS3, which was highly expressed in the root and strongly induced by flooding treatment, was chose for the further research. Via histochemical, subcellular localization and antisense suppression of CsSUS3 in cucumber, we found that CsSUS3 played an important role in resisting hypoxic stress. © 2013 John Wiley & Sons Ltd.