Figure 5.

Identification of SERKs as co-receptors for RGF1. (A) RGF1 induces RGFR1^LRR-SERK1^LRR interaction in vitro. Left, superposition of the gel filtration chromatograms of the RGFR1^LRR+SERK1^LRR and RGFR1^LRR+RGF1+SERK1^LRR proteins. The vertical and horizontal axes represent UV absorbance (280 nm) and elution volume (ml), respectively. Right, coomassie blue staining of the peak fractions shown on the left following SDS-PAGE. M, molecular weight ladder (kDa). (B) RGF1 induces RGFR2^LRR-SERK1^LRR interaction in vitro. Left, superposition of the gel filtration chromatograms of the RGFR2^LRR+SERK1^LRR and RGFR2^LRR+RGF1+SERK1^LRR proteins. (C) RGF1 promotes RGFR1^ΔKD-SERK1^ΔKD/SERK2^ΔKD/BAK1^ΔKD interaction in Nicotiana Benthamiana. Agrobacteria harboring the indicated constructs were syringe infiltrated into tobacco leaves. Peptides (10 nM RGF1, 1 μM PSK as a negative control) were added 2 h before tobacco tissues were harvested for immunoprecipitation with anti-GFP antibody. Immunoblot assays were performed to determine the levels of expressed proteins. Each assay was repeated three times. (D) RGF1 promotes RGFR3^ΔKD-SERK1^ΔKD, RGFR4^ΔKD-SERK1^KD and RGFR5^ΔKD-SERK1^ΔKD interaction in Nicotiana Benthamiana. (E) Confocal images of the root meristem of Col-0 and mutants (5 DAG stage). The white arrowheads indicate the boundary of meristematic zone and elongation zone. Scale bar, 50 μm. (F) Changes in meristematic cortex cell numbers in Col-0 and serk mutants in response to RGF1. Quantification of meristematic cortex cell number of Col-0 and mutant seedlings (5 DAG stage) grown in the medium supplied with 1 nM RGF1. n = 25. (G) Root lengths of Col-0 and serk mutant seedlings (7 DAG stage). (H) Changes in root lengths of Col-0 and serk mutants in response to RGF1. Quantification of root lengths of Col-0 and mutant seedlings (7 DAG stage) grown in the medium supplied with 1 nM RGF1. n = 25. ^*P < 0.05, ^**P < 0.01, ^***P < 0.001 by Student's t-test. NS indicates not significant.