Fig. 6: A working model for self-organizing transient auxin flow at cotyledon’s margins. | Nature Communications

Fig. 6: A working model for self-organizing transient auxin flow at cotyledon’s margins.

From: PIN2-mediated self-organizing transient auxin flow contributes to auxin maxima at the tip of Arabidopsis cotyledons

Fig. 6

Cotyledon’s margins display a transient self-organized PIN2-mediated auxin transport towards the tip. a Schematic at a cell level. First, a positive feedback (24-48 HAP) via IBA-derived auxin promotes PIN2 expression and PIN2 apical polar accumulation Then, a negative feedback (60-72 HAP) is turned on where auxin induces the expression of TOB1 to sequester IBA into vacuoles, reducing IBA-derived auxin and leading to down regulation of PIN2 and cessation of the auxin flow. b Schematic at a tissue level. At 24 HAP, ECH2 is accumulated along the margin (purple) before PIN2 (green), catalyzing IBA-derived auxin (red). PIN2-based auxin transport moves auxin towards the cotyledon tip. At 48 HAP, higher auxin levels at MCs closer to the tip (red gradient upwards) triggers expression of TOB1 (upwards yellow gradient). TOB1 localizes to the tonoplast gradually from tip-to-base. Tonoplast TOB1 reduces IBA-derived auxin, leading to the reduction of PIN2 levels (downwards green gradient). At 72 HAP, the auxin transport system is completely shut down (gray arrow), which coincides with strong tonoplast TOB1 (dark yellow). At this point, a fully interdigitated field of pavement cells is observed.

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