Characterization of New Gibberellin-Responsive Semidwarf Mutants of Arabidopsis

Chemical mutagenesis of Arabidopsis thaliana (L.) Heynh. yielded four semidwarf mutants, all of which appeared to be gibberellin (GA)-biosynthesis mutants. All four had atypical response profiles to C20-GAs, suggesting that each had impaired 20-oxidation. One mutant, 11.2, was shown to be allelic to ga5 and has been named ga5-2. It had altered metabolism of [14C]GA15 relative to that in wild-type plants and undetectable levels of C19-GAs in young stems, consistent with the known function of GA5 as a stem-expressed GA 20-oxidase. Two mutants (2.1 and 10.3), which had very short inflorescences and siliques, were allelic to each other but not to the known GA-responding mutants, ga1 to ga5. The locus defined by these two mutations is provisionally named GA6 and is purported to encode an inflorescence- and silique-expressed GA 20-oxidase. A double mutant, ga5-2 ga6-2, had an extreme dwarf phenotype with very short siliques. The fourth mutation, 1.1, gave a phenotype like ga5, but was not allelic to any of the known ga mutations. It has not yet been given a gene symbol pending further studies.