The Style -Locus Gene Possesses Brassinosteroid-Inactivating Activity When Expressed in .

Heterostyly distinct hermaphroditic floral morphs enforce outbreeding. Morphs differ structurally, promote cross-pollination, and physiologically block self-fertilization. In the self-incompatibility (S)-locus controlling heterostyly possesses three genes specific to short-styled morph genomes. Only one gene, , is expressed in pistils and this has been hypothesized to possess brassinosteroid (BR)-inactivating activity. We tested this hypothesis using heterologous expression in as a bioassay, thereby assessing growth phenotype, and the impacts on the expression of endogenous genes involved in BR homeostasis and seedling photomorphogenesis. Transgenic expressing displayed phenotypes typical of BR-deficient mutants, with phenotype severity dependent on expression level. , which encodes an enzyme involved in BR inactivation, was downregulated in -expressing lines. and which encode enzymes involved in BR biosynthesis, were upregulated. Hypocotyl growth of dwarfs responded to application of brassinolide in light and dark in a manner typical of plants over-expressing genes encoding BR-inactivating activity. These results provide empirical support for the hypothesis that TsBAHD possesses BR-inactivating activity. Further this suggests that style length in is controlled by the same mechanism (BR inactivation) as that reported for , but using a different class of enzyme. This reveals interesting convergent evolution in a biochemical mechanism to regulate floral form in heterostyly.