The Turnera Style S-Locus Gene TsBAHD Possesses Brassinosteroid-Inactivating Activity When Expressed in Arabidopsis thaliana

The Turnera Style S-Locus Gene TsBAHD Possesses Brassinosteroid-Inactivating Activity When Expressed in Arabidopsis thaliana

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Heterostyly distinct hermaphroditic floral morphs enforce outbreeding.Morphs differ structurally, promote cross-pollination, and physiologically block self-fertilization.In Turnera the self-incompatibility (S)-locus controlling heterostyly possesses three genes specific to short-styled morph genomes.Only one LIP TINT gene, TsBAHD, is expressed in pistils and this has been hypothesized to possess brassinosteroid (BR)-inactivating activity.We tested this hypothesis using heterologous expression in Arabidopsis thaliana as a bioassay, thereby assessing growth phenotype, and the impacts on the expression of endogenous genes involved in BR homeostasis and seedling photomorphogenesis.

Transgenic A.thaliana expressing TsBAHD displayed phenotypes typical of BR-deficient mutants, with phenotype severity dependent on TsBAHD expression level.BAS1, which encodes an enzyme involved in BR inactivation, was downregulated in TsBAHD-expressing lines.CPD and DWF, which encode enzymes involved in BR biosynthesis, were upregulated.Hypocotyl growth of TsBAHD 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 Turnera is controlled by the same mechanism (BR inactivation) as that reported for Primula, but using a different class of enzyme.This TV Tuner Cards reveals interesting convergent evolution in a biochemical mechanism to regulate floral form in heterostyly.