Cloning of 9-cis-epoxycarotenoid dioxygenase gene (TaNCED1) from wheat and its heterologous expression in tobacco

Abscisic acid (ABA) regulates plant responses to various environmental stresses. Oxidative cleavage of cis-epoxycarotenoids catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED) is the critical step in the biosynthesis of ABA in higher plants. Using a homologous cloning approach, a NCED-like gene (designated as TaNCED1) was isolated from wheat (Triticum aestivum). It contained an open reading frame of 1 848 bp and encodes a peptide of 615 amino acids. Multiple sequence alignments showed that TaNCED1 shared high identity with NCEDs from other plants. Phylogenetic analysis revealed that TaNCED1 was most closely related to a barley HvNCED1 gene. The predicted 3D structure of TaNCED1 showed high similarity with other homologues. Southern blot analysis indicated that TaNCED1 was a single copy in the genome of wheat. TaNCED1 was differentially expressed in various organs and the expression was up-regulated by low temperature, drought, NaCl, and ABA. Heterologous expression of TaNCED1 in tobacco (Nicotiana tabacum) significantly improved its drought tolerance. Under drought treatment, TaNCED1-overexpressing transgenic tobacco plants exhibited higher germination rate, higher relative water content, content of soluble sugars and of ABA when compared with the wild type plants.