For plants, accurate timing of the transition from vegetative to reproductive growth maximizes reproductive success. The transition is known to be controlled by numerous interacting endogenous and environmental factors,but more, it seems, remain to be discovered. On , Domagalska and colleagues describe an unexpected role for brassinosteroid signalling -namely, the regulation of expression of FLOWERING LOCUS C(FLC), a potent floral repressor - in the control of flowering time in Arabidopsis thaliana. Brassinosteroids are plant steroid hormones that signal through a receptor-like kinase called BRASSINOSTEROID INSENSITIVE 1 (BRI1). The researchers identify two alleles of bri1 that are strong enhancers of several flowering-time mutants. Double mutants that combine bri1 (or cpd, a brassinosteroid-deficient mutant)with known flowering-time mutants (for example, luminidependens)express raised levels of FLC transcripts, they report, which leads to extremely late flowering. RNAi directed against the FLC transcript reverses this phenotype. The researchers propose, therefore, that brassinosteroid signalling regulates FLC expression and thus helps to control flowering time.
