Abstract
In the last decade, the first brassinosteroid (BR) signaling mutant bril (brassinosteroid insensitive 1), identified in Arabidopsis, has been at the center of topics on BR perception. The structure of BRI1 and its plasma membrane location together with other experimental results had BRI1 a leading candidate for BR-receptors. During these five years, our collaborative researches on BRI1, jointing molecular biology and organic chemistry, have brought about great progress in understanding BR perception mechanism. It is now clarified that BR binds directly to the extracellular domain of BRI1 at the minimal binding region including the 70-amino acid island, showing that BRI1 is a BR-receptor and a new binding domain for steroid hormones. In this work, BR-based molecular probes played a crucial role. Tritium-labelled brassinolide with a high specific radio-activity (50 Ci/mmol) and a biotin-tagged photoaffinity castasterone were absolutely essential for binding studies and for photoaffinity labeling experiments, respectively.
