Figure 9.

VHP domain of VLN4 contributes to the effect of TIBA on actin dynamics and PAT in Arabidopsis. A, Representative images of root epidermal cells from wild-type (WT), vln4-1, and vln4-1–complemented lines. Seedlings were treated with mock or 10 µm TIBA for 5 min. Bar = 10 µm. B and C, Actin architecture analyses were performed on images shown in A. D, Basipetal auxin transport was detected in the roots treated with 30 µm TIBA for 15 h. E, The percentage inhibition of PAT in seedlings treated with TIBA relative to the mock control was calculated. Values given are means ± se (for actin architecture analysis, n > 300 images from 25 seedlings for each genotype and treatment; for PAT analysis, n = 15 roots for each genotype and treatment; for calculating the percentage inhibition, data were from five replicates; a, significantly different from mock control within the same genotype; b, significantly different from wild-type treated with mock; c, no significant difference from mock control within the same genotype; d, no significant difference from wild-type treated with mock; e, significantly different from vln4-1 complemented with full-length VLN4 within the same treatment; f, no significant difference from vln4-1 complemented with full-length VLN4 within the same treatment; * P < 0.05; **P < 0.01; t test; Pearson’s χ² test was applied to evaluate significant differences in the frequency distribution across intensity classes between treatments). F, Schematic illustration summarizing VLN4 as a direct-binding target of TIBA to regulate actin dynamics and PAT. TIBA stimulates actin bundling and suppresses filament turnover in a VLN4-dependent fashion, leading to a more bundled cortical actin array in cells. The changes in actin organization and dynamics alter PIN2 localization and trafficking, which are critical for the maintenance of PAT. Solid and dashed lines indicate verified and unclear interactions, respectively.