Expression pattern and promoter analysis of the gene encoding GDP-D-mannose 3′,5′-epimerase under abiotic stresses and applications of hormones by kiwifruit

In higher plants, ascorbic acid (AsA) plays important roles in antioxidative defenses against environmental stresses. GDP-D-mannose 3',5'-epimerase (GME) catalyses a committed step in AsA biosynthesis. After isolating GME cDNAs from two species of Actinidia (kiwifruit), we analyzed expression abundance and promoter activities under abiotic stresses or applications of exogenous stress-signaling hormones. Exposure to ABA, SA, cold or light by kiwifruit leaves increased AsA contents, whereas application of GA(3), wounding, heat or darkness decreased those amounts. Expression of GME was up-regulated in the leaves by SA, wounding, cold, and heat, but down-regulated by GA(3). Promoter activities were enhanced by SA and heat, but were not affected by wounding, darkness, or light. GME promoters affected differentially by some stress conditions or stimuli between two kiwifruit genotypes used, although AsA levels are not linked with the expression of GME, indicating other factors are important for determining AsA levels. We speculated that AsA concentrations are under complicated regulation so that only one gene expression, here GME sole cannot determine AsA concentrations. (C) 2012 Elsevier B.V. All rights reserved.