Interaction Between Photoreceptors and BR Signaling in Arabidopsis

Extensive studies have been performed to elucidate the role of brassinosteroids (BRs), an important class of phy- tohormone in plant growth, development, and photomorphogenesis. Different wavelengths of light recognized by photoreceptors play a crucial role in plant development. The role of different photoreceptors in BR signaling has not been analyzed. Here we used photoreceptor single mutants, double mutants and even a quadruple mutant to analyze BR-dependent hypocotyl growth and gene regulation. All the photoreceptor mutants differed from the controls in their response to BR, and hypocotyl elongation as well as BR marker gene regulation were inhibited by application of propiconazole (PCZ), a BR biosynthesis inhibitor. In addition, altered Phytochrome and Cryptochrome expression in brassinosteroid insensitive 1 mutant bri1-5 and brassinazole-resistant 1 dominant mutant bzr1-D indicated that BR negatively regulates photoreceptors in transcriptional levels. This is the first study to investigate the connections between BR and photoreceptors in Arabidopsis .