Figure 3.

The protease inhibitor activity of CYS6 is required for elf18-triggered resistance. A) Structure of CYS6 as determined by SMART (http://smart.embl-Heidelberg.de/). The N-terminal box indicates the predicted signal peptide, the middle box represents the cystatin (CY) domain, and the C-terminal bar is a low-complexity region. The amino acids mutated in CYS6m are marked in red. B)E. coli–produced GST, GST-CYS6 (CYS6), and GST-CYS6m (CYS6m) were used to test their inhibition on papain with E64 as a positive control. The products of papain digestion were detected by measuring the optical density at 420 nm. Significant differences compared with the CK samples were detected by Student’s t test. Data are shown as means ± Sd (n = 3). C) Relative expression levels of CYS6 and CYS6m in their transgenic lines in the cys6 mutant background. Significant differences compared with the cys6 mutant were detected by Student’s t test. Data are shown as means ± Sd (n = 3). D) Overexpressing CYS6 but not CYS6m rescues the deficiency of elf18-triggered resistance in the cys6 mutant. Experiments were performed as described in Fig. 2A. Significant differences were detected by 2-way ANOVA. Data are shown as means ± Sd (n = 8). *P < 0.05; ***P < 0.001; ****P < 0.0001; ns, no significant difference.