Fig. 4

Changes in early PP biosynthesis alter the auxin response. a Decreased auxin sensitivity of OE#1 plants is reversed by t-CA. Five-day-old plants were transferred to vertical plates with the auxin 1-naphthaleneacetic acid (NAA), t-CA or both and the primary root length was measured after 6 days of growth. Data are shown as absolute root length ± SD (n ≥ 12). The significance of the difference between the NAA and the combined NAA and t-CA treatments of OE#1 plants is shown (ns, not significant and ****, P < 0.0001; two-way ANOVA with Bonferroni’s multiple comparisons test). b The ref3–1 mutant is hypersensitive to auxin. The assay was performed as in a. Data are presented as relative root length with the mean of the control treatment assigned the value of 1. Error bars are SD (n ≥ 10) and the significance of the difference between Ler and ref3–1 for each treatment is shown (*, P < 0.05; ****, P < 0.0001; two-way ANOVA with Bonferroni’s multiple comparisons test). c Piperonylic acid (PA) treatments induce DR5::GUS expression in a dose-dependent manner. Four-day-old seedlings were co-treated with NAA and a range of PA doses. The GUS reactions were stopped upon the visible accumulation of the GUS product in the 0.3 μM PA-treated seedlings (i.e., before blue color formation in the NAA-treated control seedlings) to allow visualization of the differences in DR5::GUS expression. d Cytokinin hypersensitivity of ref3–1 is blocked by the auxin response inhibitor auxinole (Axl). The assay was performed as in a. Significant differences between treated and control samples for each line is noted (in black for the wild type and in blue for the mutant) as well as the significance of the difference between the BA and the combined BA and Axl treatments of OE#1 plants (**, P < 0.01; ****, P < 0.0001; two-way ANOVA with Bonferroni’s multiple comparisons test). e Overexpression of KMD1/KFB20 is sufficient to suppress auxin hypersensitivity of the ref3–1 mutant. The assay was performed as in a. The significance of the difference between the control and NAA-treated plants is shown (ns, not significant and ***, P < 0.001; two-way ANOVA with Bonferroni’s multiple comparisons test)