Fig. 6: Fusarium SCOOP-like peptides activate MIK2-dependent immune responses.

a Alignment of SCOOPL SxS motifs from different Fusarium strains with Arabidopsis SCOOP12. Foc, F. oxysporum f. sp. conglutinans Fo5176; Fol, F. oxysporum f. sp. lycopersici MN25; Fo47, F. oxysporum 47; Fg, F. graminearum PH-1; Fpg, F. pseudograminearum; Ff, F. fujikuroi; Fv, F. venenatum. Two conserved serine (S) residues are boxed in red. b The surface accessibility of FgSCOOPL. FgSCOOPL peptide is highlighted in magenta, the C-terminus in yellow, and the rest in green. c Fusarium SCOOPL peptides, except FpgSCOOPL, inhibit root growth in a MIK2-dependent manner. Images of 10-day-old WT and mik2-1 seedlings with or without 1 µM Fusarium SCOOPL peptides. Scale bar, 4 mm (left). Quantification of seedling root length (right) (***P < 0.001, n.s., no significant differences, two-tailed Student’s t-test, n = 9, 9, 8, 9, 9, 10, 9, 9, 8, 9, 10, 9 for plots from left to right). d Fusarium SCOOPLs, except FpgSCOOPL, induce ROS production. WT seedlings were treated with or without 1 µM peptides, and ROS was calculated as total RLUs. Different letters indicate a significant difference with others (P < 0.05, one-way ANOVA followed by Tukey’s test, n = 4). e FocSCOOPL triggers the cytosolic Ca²⁺ increase. p35S::Aequorin seedlings were treated with or without 1 µM FocSCOOPL or FpgSCOOPL. Cytosolic Ca²⁺ concentration was indicated as means of RLU. The data are shown as mean ± SE (n = 9 and 6 for FocSCOOPL and FpgSCOOPL). f FocSCOOPL-induced MAPK activation is blocked in mik2-1. Ten-day-old seedlings were treated with or without 1 µM FocSCOOPL. g Fusarium SCOOPLs induce pMYB51::GUS expression in roots. Images of root tips of 1-week-old pMYB51::GUS seedlings upon treatments with or without 1 µM SCOOPLs for 3 h and subjected to GUS staining. Scale bar, 1 mm. h, i FocSCOOPL-induced ROS production is blocked in mik2 (h), and in bak1-4, bak1-5/serk4, bik1/pbl1, and rbohD mutants (i). One-week-old seedlings were treated with 1 µM FocSCOOPL, and ROS production was calculated as total RLUs. Different letters indicate a significant difference with others (P < 0.05, one-way ANOVA followed by Tukey’s test, n = 6, 6, 4 for plots from left to right in (h), n = 3 in (i)). j FocSCOOPL induces MIK2-BAK1 association. The experiment was performed as in Fig. 5f. Box plots in c, d, h, and i show the first and third quartiles as bounds of box, split by the medians (lines), with whiskers extending 1.5-fold interquartile range beyond the box, and minima and maxima as error bar. Experiments in (c–j) were repeated three times with similar results.