Tuber-Specific Expression of Two Gibberellin Oxidase Transgenes from Arabidopsis Regulates over Wide Ranges the Potato Tuber Formation

Potato (Solanum tuberosum L.) tuberization is a practically important natural process regulated by various factors including phytohormones. This work was aimed at studying characteristics of in vitro cultivated potato plants transformed with the AtGA20-oxidase gene promoting biosynthesis of bioactive gibberellins (GAs) or with the AtGA2-oxidase gene acting oppositely, i.e. deactivating functional GAs. Both transgenes originated from Arabidopsis and were fused to a sugar-sensitive B33 patatin promoter providing their expression predominantly in tubers. Global phytohormone determination in AtGA20ox-transformants revealed active GA₁ at high and moderate concentrations in tubers and shoots, respectively. In control plants, GA₁ was virtually absent. Together with GAs, contents of some other phytohormones were altered in transgenic plants. This was especially true for the auxin content which increased ~15-fold in tubers and more than 4-fold in shoots. Also the jasmonic acid content exhibited a tuber-specific increase while the content of abscisic acid decreased both in tubers and shoots. The dynamics of tuberization in transformed and non-transformed potato plants was recorded in in vitro parallel assays. The transgene for GA inactivation enhanced tuber formation while the transgene promoting active GA synthesis reduced potato productivity. Hence, the crucial role of gibberellin in potato productivity was corroborated. These results showed that the manipulation of the local GA level by using the foreign GA oxidase genes and organ-specific promoters is useful not only to investigate the molecular mechanisms governing tuberization, but also as a biotechnological tool for the manipulation of tuber formation without marked impairment of other physiological traits of potatoes.