Petal-specific activity of the promoter of an anthocyanidin synthase gene of tobacco (Nicotiana tabacum L.)

Anthocyanidin synthase (ANS) is a key enzyme in the late stages of the biosynthesis of anthocyanins, an important class of plant pigments. Two ANS genes (NtANS1 and NtANS2) were cloned from flowers of the tobacco plant (Nicotiana tabacum). These genes exhibit similar genomic structures and are present as single-copy genes. Sequence analysis of the coding regions of the tobacco ANS genes has revealed high levels of amino acid identity with ANS proteins of other plants, with 70–87 % homology at the amino acid level. Analysis of the spatial regulation of expression of tobacco ANS genes has revealed that levels of their transcripts are particularly abundant in petal tissues, among all organs (leaf, stem, root, flower, and seed) and flower tissues (petal, pistil, stamen, and sepal) analyzed. Moreover, levels of gene expression increase with maturation, and then decrease slightly during the final stages of flower development. To investigate activity of the promoter of the NtANS1 gene, the cis-acting elements in the 955-nucleotide region upstream of its start codon are analyzed. Placing the expression of the gene that encodes β-glucuronidase (GUS) under the control of the NtANS1 promoter (NtANS1-P) in transgenic tobacco plants enables the authentic petal-specific expression of this gene to be verified by analysis of different flower tissues by histochemical GUS staining, semi-quantitative RT-PCR, and fluorometric GUS assays. In conclusion, given the ability of the NtANS1-P to restrict target gene expression to petals, it might have value in engineering desirable changes in petal color in the flowers of genetically modified plants.