ABSTRACT
Polarized movement of auxin generates concentration gradients within plant tissues to control cell division patterns and growth direction by modulating microtubule organization. In this study, we identify a reverse mechanism, wherein microtubules influence polar auxin transport. We show that the microtubule-associated protein CLASP interacts with the retromer component sorting nexin 1 (SNX1) to mediate an association between endosomes and microtubules. clasp-1 null mutants display aberrant SNX1 endosomes, as do wild-type plants treated with microtubule-depolymerizing drugs. Consistent with SNX1's role in trafficking of the auxin efflux carrier PIN-FORMED2 (PIN2), clasp-1 mutant plants have enhanced PIN2 degradation, and PIN2 movement to lytic vacuoles is rapidly induced by depolymerization of microtubules. clasp-1 mutants display aberrant auxin distribution and exhibit numerous auxin-related phenotypes. In addition to mechanistically linking auxin transport and microtubules, our data identify a ubiquitous endosome-microtubule association in plants.
