Dual auxin signaling pathways control cell elongation and division

Auxin regulates plant cell division, elongation, and differentiation through signal transduction that probably embodies a complex network rather than a linear pathway. Evidence has emerged that auxin-binding protein 1 (ABP1) is a component of this signal network by acting as a high-affinity auxin receptor mediating cell expansion. On the other hand, high auxin concentrations stimulate cell division via a second, unidentified auxin pathway, possibly mediated by a low-affinity auxin receptor. Evidence is presented that this second pathway is coupled with a heterotrimeric G-protein. Molecular genetic evidence supports the conclusion that both the ABP1 and G-protein pathways must crosstalk to bring about normal development.