The NCED2 and CYP707A1 Genes of Wheat Regulate Seed Dormancy and Germination

Abscisic acid (ABA) controls seed germination and dormancy, and this is mediated partly by its level in the seed. The amount of ABA in plant tissues is determined by a balance between its biosynthesis and catabolism, which are regulated mainly by the 9-cis-epoxycarotenoid dioxygenases (NCEDs) and ABA 8′-hydroxylase (ABA8′OH), respectively. This study identified the three homeologs of one of the NCED genes of hexaploid wheat, designated as TaNCED2 (TaNCED2A, TaNCED2B and TaNCED2D), and one of the ABA8′OH encoding CYP707A genes, designated as TaCYP707A1 (TaCYP707A1A, TaCYP707A1B and TaCYP707A1D) from a dormant cultivar. Expression analysis of TaNCED2 and TaCYP707A1 in different wheat tissues revealed that both genes are mainly expressed in the seed. Ectopic constitutive expression of the TaNCED2A homeolog in wild-type Arabidopsis led to increased seed ABA content during imbibition and delayed germination relative to the wild-type control seeds, while constitutive expression of the TaCYP707A1B homeolog in wild type Arabidopsis plants caused a decrease in seed ABA level and enhanced germination phenotype. Complementation of the cyp707a1 cyp707a2 double mutant seeds with TaCYP707A1B significantly reduced seed ABA level and there by rescued the germination phenotype cyp707a1 cyp707a2. Furthermore, the expression patterns of the two gene in wheat seeds were found to be closely associated the degree of seed dormancy.