Hormonal control of flowering: Molecular mechanisms of hormone-receptor action

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Little is known regarding hormone-receptor events that mediated the developmental switch from the vegetative to reproductive habit. We conducted a modifier mutagenesis in Arabidopsis and isolated the brassinolide receptor BRI1 as a timing regulator. Further efforts established the genetic node of its modifying activity, and the potent floral repressor FLC was found to be the molecular target of BRI1. As BRI1 encodes a receptor kinase, we are intrigued as to the biochemical mechanism from a membrane protein that leads to the floral-timing genetic program. Analysis of a separately isolated mutation surprisingly lead to our discovery of another receptorkinase family that participates in floral timing, termed here the RCF loci. Genetic and molecular analyses implicate these receptors in gibberellin signaling. We consider it of broad interest to characterize the RCF proteins as the "missing" hormone receptor for gibberellin. Collectively, our proposal to work on hormone-receptor mediation of the floral transition will open up mechanistic understandings of a poorly understood biological phenomenon. As such, these efforts should lead to ground-breaking understating of hormonal control of a timing process.