Isolation and characterization of an ABC-transporter cDNA clone from wheat (Triticum aestivum L.)

The outmost layer of the surface of any land plant is covered with wax, which protects the inner tissues of plants. The Arabidopsis ATP binding cassette (ABC) transporter, Cer5, was found to be an exporter of wax molecules. Full-length wheat tacer5 cDNA, a sequence homologous to cer5, was isolated. Similar to other transporters of the ABCG subfamily, TaCer5 also has a typical basic structure of NBD-MSD (nucleotidebinding folds domain — membrane-spanning domain). Although the identity scores of TaCer5 and other ABCG transporters are not very high, amino acid residues of NBDs and MSDs are highly conserved among them. Tacer5 is a tissue-specific gene. The transcripts of tacer5 were found in leaf tissues and predominantly in stem tissues but were hardly detectable in root tissues. Stress inhibited the expression of tacer5. The expression was significantly decreased by salinity, low temperature, and 48-hour-darkness and also by exogenous phytohormone abscisic acid and salicylic acid, although not significantly. Exposure to polyethylene glycol either increased the expression or decreased it, depending on the duration of exposure. All the above factors also decreased the extent of wax deposited on wheat leaves. It is therefore concluded that transport of wax molecules is affected by environmental factors.