Extended Data Fig. 6: BRX auxin response and PAX specificity.

a, b, Response of BRX–CITRINE fusion protein to treatment with 1 μM or 10 μM auxin (NAA), time course experiment (b) with quantification (a, means from approximately ten cells per root, arbitrary units). Statistically significant differences are indicated (two-sided Student’s t-test; a, mock versus others, P < 0.0094; b, 1 μM versus 10 μM auxin, P < 0.0028). c, Phosphoproteomics of auxin-treated seedlings, showing normalized abundance of a conserved phosphosite in PAX, D6PK, D6PKL1-3, and AGC1-6, with subfragments indicated in different colours. d, Same as c, for a PIN1 phosphosite. e, Radioactive in vitro kinase assays with GST fusion proteins of D6PK, PAX, or PAX(S596A) and PAX(S596D) point mutants, with BRX or the PIN1 cytosolic loop as substrate (top) and corresponding loading controls (bottom). f, Auxin transport assays performed in X. laevis oocytes expressing the indicated heterologous plant proteins (n = 10 oocytes per time point; error bars, s.e.m.). g, Polar localization of the YFP–PAX(S596D) variant in developing PPSEs of a pax mutant. h, Quantification of gap-cell frequency in protophloem strands of seven-day-old pax mutant seedlings that express a D6PK–CITRINE fusion protein under the control of the PAX promoter. The statistically significant difference is indicated (two-sided Fisher’s exact test; a, Col-0 versus pax and transgenic lines, P < 0.0001). i, Polar localization of D6PK–CITRINE fusion protein in developing PPSEs of a pax mutant. j, k, Auxin induction of BRX transcription in developing PPSE cell files (asterisks) visualized using an NLS–3×VENUS reporter gene (j), with corresponding quantification of nuclear fluorescence signal (k). Statistically significant differences are indicated (one-sided Student’s t-test; a, versus preceding time point, P < 0.0153).