a, BIK1(9KR) undergoes phosphorylation similar to BIK1 upon flg22 treatment. BIK1–HA or BIK1(9KR)–HA was expressed in wild-type protoplasts which were then treated with 100 nM flg22 for the indicated times. Band-shift of BIK1 was examined by immunoblotting with anti-HA antibody. b, BIK1(9KR) interacts with RHA3A in a co-IP assay. RHA3A–HA was co-expressed with BIK1–FLAG or BIK1(9KR)–FLAG in protoplasts that were then treated with 100 nM flg22 for 15 min. Co-IP assay was carried out with anti-FLAG agarose and immunoprecipitated proteins were immunoblotted with anti-HA or anti-FLAG antibody (top two panels). Bottom two panels show BIK1–FLAG or BIK1(9KR)–FLAG and RHA3A–HA proteins. c, Transgenic plants with BIK19KR overexpression in wild-type background show similar MAPK activation to wild-type plants. Eleven-day-old seedlings of wild-type or 35S::BIK19KR-HA/WT transgenic plants (lines 55 and 56) were treated with 200 nM flg22 for 15 min. MAPK activation was analysed with anti-pERK antibody (top), and protein loading is shown by CBB staining for RBC (bottom). d, Transgenic plants with BIK19KR overexpression in wild-type background show similar flg22-induced ROS production to wild-type plants. Leaf discs from the indicated genotypes were treated with 100 nM flg22, and ROS production was measured as relative luminescence units by a luminometer over 50 min. Mean total photon count ± s.e.m. overlaid with dot plot (one-way ANOVA, n = 16). e, Growth phenotype of pBIK1::BIK1-HA/bik1 and pBIK1::BIK19KR-HA/bik1 transgenic plants. Five-week-old soil-grown plants are shown. Scale bar, 1 cm. f, Expression of BIK1–HA or BIK1(9KR)–HA in transgenic plants. Top, total proteins from leaves of four-week-old transgenic plants were subjected to anti-HA immunoblotting. Bottom, CBB staining for RBC. g, RHA3A and RHA3B are involved in resistance to Pst DC3000 hrcC− infection. Plants were spray-inoculated with Pst DC3000 hrcC− and bacterial growth was measured at 4 dpi. Mean ± s.e.m. overlaid with dot plots (one-way ANOVA, n = 6). h, RHA3A and RHA3B are involved in resistance to Botrytis. Four-week-old plant leaves were deposited with 10 μl B. cinerea BO5 at a concentration of 2.5 × 105 spores per ml. Disease symptoms were recorded, and the lesion diameter was measured at 2 dpi. Mean ± s.e.m. overlaid with dot plots (one-way ANOVA, n = 34). i, ROS production is reduced in rha3a/b plants. Leaf discs from wild-type or rha3a/b plants were treated with 100 nM flg22 and ROS production measured over 50 min. Mean ± s.e.m. total photon count overlaid with dot plots (two-tailed Student’s t-test, n = 36 for wild-type and n = 32 for rha3a/b). j, RHA3A and RHA3B are involved in resistance to Pst DC3000. Plants were spray-inoculated with Pst DC3000 and bacterial growth was measured at 3 dpi. Mean ± s.e.m. overlaid with dot plots (two-tailed Student’s t-test, n = 9). Experiments were repeated three times with similar results. Source Data