Fig. 4.

Phosphorylation of BRI1 at the serine-891 site affects plants growth. (A, Top) Wild-type BRI1–Flag and the S891A-directed mutant rescue the dwarf phenotype of bri1-5 plants, whereas the S891D-directed mutant does not. (Middle and Bottom) Three independent transgeninc lines of each directed mutant, and the immunoblots show equal expression of the BRI1–Flag transgene. (B) Hypocotyl and petiole lengths measured 6 d after seed germination for plants grown in soil with a short day photoperiod (8 h light/16 h dark). Values are means of measurements from 10 seedlings ± SEM. (C) The S891A-directed mutant accumulates more unphosphorylated BES1 protein in response to exogenous BL treatment, whereas the S891D mutant is unresponsive. Values plotted are from two independent experiments. A representative immunoblot from which these results were obtained is presented in Fig. S2.