Skip to main content
Figure 2 | Genome Biology

Figure 2

From: Cytokinin and auxin intersection in root meristems

Figure 2

Model for positioning the root transition zone. (a) In the Arabidopsis root, basipetal auxin transport generates an auxin maximum at the stem-cell niche (STN) where it is required for stem-cell specification [4, 16]. Cell division is confined to the proximal meristem (PM), and cells differentiate and elongate in the elongation differentiation zone (EDZ). The transition zone (TZ) is the boundary between dividing and expanding cells. (b) Meristem size, defined as the number of cells in a cell file in the proximal meristem, is determined by rates of cell division in the meristem and differentiation at the transition zone. Perturbations favoring cell division increase meristem size, whereas those favoring differentiation decrease meristem size. Cell division is maintained in the proximal meristem by the presence of high auxin concentrations. Auxin activity is antagonized in the transition zone by cytokinin synthesized in the vasculature, which induces expression of SHY2 through the AHK3/ARR1, ARR12 cytokinin signaling pathway. SHY2 represses auxin responses and represses PIN expression, limiting lateral auxin transport and enabling cell differentiation and elongation. SHY2 also regulates the cytokinin biosynthesis enzyme IPT5. SHY2 is itself regulated by auxin; it is marked for proteasome degradation through auxin-dependent recognition by the SCFTIR1 complex.

Back to article page