Abstract
PHYTOCHROME INTERACTING FACTOR 3 (PIF3) interacts with the active phytochrome B (phyB). To identify mutations in the phyB N-terminus that disrupt this interaction, we developed a yeast reverse-hybrid screen. Fifteen mutations identified in this screen, or in previous genetic screens for Arabidopsis mutants showing reduced sensitivity to red light, were shown to disrupt light-induced binding of phyB to PIF3 in in vitro binding assays. These phyB mutations fall into two classes: Class I (11 mutations) containing those defective in light perception, and Class II (4 mutations) containing those normal in light perception, but defective in binding to PIF3. A bioinformatics comparison of phyB to BphP, for which a crystal structure has been solved, predicts that three of the four Class II mutated residues are solvent exposed in a cleft between PAS and GAF domains, suggesting that these residues could be directly required for the physical interaction of phyB with PIF3.
