Characterization of a sterile dwarf mutant and the cloning of zeaxanthin epoxidase in Asian cotton (Gossypium arboreum L.)

Abstract

To document radiation damage incurred by nuclear DNA and understand the molecular mechanisms that control plant height, a sterile dwarf mutant (sd a ) derived from the Gossypium arboreum treated with 60Co γ-rays was characterized. A sequence analysis revealed that sd a included a partial deletion and a point mutation. The physiological changes and responses of the sd a mutant to exogenous hormones showed that the mutant’s chlorophyll contents, net photosynthetic rate, and abscisic acid levels were significantly reduced compared to those of wild-type. Using the sequence of a differentially expressed sequence tag encoding a zeaxanthin epoxidase (ZEP), a novel etiolation-associated gene, full-length cDNA was rapidly cloned using rapid amplification of cDNA ends. The full-length cDNA of this gene is 2414 bp, with a 2004-bp open reading frame encoding a putative ZEP of 667 amino acid residues that has a 73.421-kDa theoretical molecular mass and a 6.67 isoelectric point. The genomic sequence of GaZEP is 5233 bp, comprising 15 exons and 14 introns. The GaZEP promoter contains numerous cis-regulatory elements that are responsive to light, hormones, and stress. Real-time quantitative PCR indicated that GaZEP expression in the mutant was downregulated. The expression levels of GaZEP in roots and leaves were positively correlated with the root hair lengths and abscisic acid levels, respectively. Thus, in photosynthetic tissues, GaZEP mRNA levels might be regulated coordinately with variations in the abscisic acid levels. These results may assist in the further functional dissection of ZEP and in elucidating the molecular mechanism underlying sterile dwarfism in cotton.