Abstract：Gibberellins (GAs) are endogenous hormones that play important roles in the regulation of plant growth and development. Their regulation functions also have a great impact on the plant's ornamental performance. Petunia is a model system for comparative research, and a model plant for investigating the traits that influence ornamental performance. Although most of the genes involved in the biosynthesis and catabolism of the bioactive GAs have been identified in Arabidopsis thaliana and rice(Oryza sativa), no GA metabolism genes in petunia (Petunia hybrida) had been cloned and analysed previously. In this study, three full-length GA 2-oxidase cDNAs were isolated from petunia using a RACE PCR method and we named them PhGA2ox1~3(GenBank accession numbers：GU059939, JQ323102 and JQ323101). Evolutionary analysis suggested that proteins encoded by the three cDNAs all belong to C19 CGA 2-oxidase clade, closing to SlGA2ox2, -4, and -5 of Solanum lycopersicum and NtGA2ox1~3 of Nicotiana tabacum. qRT-PCR analysis indicated that their expression profiles were similar. A relatively higher expression level was observed in stems, leaves, stamens and pistils on the first day of anthesis, and in wilting petals, compared to a very low expression level in sepals and petal on the first day of anthesis and in fruits seven days after pollination. However, PhGA2ox3 transcripts were much less abundant than those of PhGA2ox1 and -2 as the cycle threshold (Ct) values of PhGA2ox3 were four cycles lower than those of PhGA2ox1 and -2 for the same cDNA template (Ct PhGA2ox1~26, Ct PhGA2ox2~25 and Ct PhGA2ox3~30), using primers with similar efficiency. 2×35S::PhGA2ox1 transgenic petunia plants were created by Agrobacterium tumefaciens-mediated transformation. The transgenic plants exhibited various degrees of GA-deficient phenotypes such as shortened internodes, smaller and dark-green leaves, which were reported and well described by other researchers, suggesting the PhGA2ox1 cDNA encodes a functional gene.
