Figure 1.

Model of SYP132 function in H⁺-ATPase trafficking. A, During normal growth, SYP132 promotes internalization and recycling of inactive H⁺-ATPases to regulate apoplastic pH. B, In response to auxin, SYP132 levels are decreased, which results in increased density of active H⁺-ATPases at the PM. Proton pumping lowers the pH of the apoplast, facilitating cell wall loosening and cell expansion. C, In the presence of ABA, inactive H⁺-ATPases are internalized and targeted to the vacuole for degradation, likely along with SYP132. D, FC treatment constitutively activates H⁺-ATPases at the PM, which prevents SYP132-stimulated internalization. CME, clathrin-mediated endocytosis. Figure from Xia et al. (2019).