Cell Surface ABP1-TMK Auxin-Sensing Complex Activates ROP GTPase Signaling

A Different Route The plant hormone auxin regulates a variety of developmental processes and responses to environmental inputs, often via changes in gene transcription. Xu et al. (p. 1025 ) analyzed a signaling pathway involving ABP1 (auxin-binding protein 1) that affects the cytoskeleton and endocytosis in Arabidopsis without changing gene transcription. Instead, ABP1 functions at the cell surface to bind auxin and a family of membrane kinases, thereby activating intracellular guanosine triphosphatases to initiate important developmental changes in cell shape.