Isolation of a gibberellin 20-oxidase cDNA from and characterization of its expression in chrysanthemum

P>A PCR strategy was used to isolate a full-length GA20-oxidase cDNA from chrysanthemum. The gene putatively encodes a 377 residue polypeptide, which shares 87% homology with lettuce GA20ox. A Southern blot analysis indicated that the hexaploid chrysanthemum genome probably contains several GA20ox copies. The DgGA20ox gene is expressed in the leaf, stem, flower and root, but most strongly in the young leaf. The application of the GA biosynthesis inhibitor paclobutrazol to the fourth internode increased the expression of DgGA20ox, while exogenously applied GA(3) decreased it. This supports the commonly observed phenomenon that the expression level of GA20ox genes is regulated by the local level of physiologically active GA. The relevance of the DgGA20ox in relation to chrysanthemum breeding was discussed as well.