Figure 2.

Model for the regulation of AHAs. Arabidopsis AHA2 is used as an example. In response to environmental and developmental signals, multiple protein kinases phosphorylate AHA2 at multiple residues, most of which are located in the C-terminal autoinhibitory R domain. Phosphorylation of Thr947, the penultimate residue, generates a binding site for activating 14-3-3 protein. Phosphorylation at other sites can lead to both activation and de-activation of AHA2 activity, e.g. by preventing binding of 14-3-3 protein. Protein kinase-mediated phosphorylation is countered by protein phosphatases, and the combined action of protein kinases and phosphatases dictates the activation status of AHA2. Colors of fonts and arrows: red, negative regulation; green, positive regulation. Solid arrows, known candidates; Dashed arrows, suggested candidates. PSY1R, PSY1 receptor; PKS5, sos2-like protein kinase 5.