Fig. 3.

BRI1 receptor activation requires heteromerization with a SERK coreceptor in planta. (A) Schematic view of signaling competent wild-type and chimeric BRI1–BL–SERK3 complexes. BRI1 domains are shown in blue, SERK3 domains in gray. (B) Stable transgenic lines expressing oBRI1–iSERK3:mCherry under the BRI promoter (pBRI1) and oSERK3–iBRI1:mCitrine under the SERK3 promoter (pSERK3) show a partially rescued bri1-301 growth phenotype when expressed together (Bottom Left). The expression of isolated chimera results in a dominant negative growth phenotype (Bottom Middle and Right). ∼WT corresponds to pBRI1::BRI1:mCitrine/bri1-null. (Scale bar, 1 cm.) (C) Hypocotyl growth assay in the presence and absence of BRZ (compare Fig. 2A). bri1-301 is hypersensitive to BRZ, a phenotype that is partially complemented by the expression of oBRI1–iSERK3 and oSERK3–iBRI1. Quantifications are shown, analyzed as in Fig. 2B.