Auxin transport: providing a sense of direction during plant development

Auxins are key regulators of plant development. Plants employ a specialized delivery system termed polar auxin transport to convey indole-3-acetic aci d from source to target tissues. Auxin transport is mediated by the combine d activities of specialized influx and efflux carriers, Mutational approach es in the model plant, Arabidopsis thaliana, have led to the molecular gene tic characterization of putative auxin influx and efflux carrier components , AUX1 and AtPIN1. Both genes belong to distinct gene families that are bei ng functionally characterized by using a reverse genetic approach in Arabid opsis. AtPIN proteins are asymmetrically localized within plant plasma memb ranes, providing a molecular mechanism for the characteristic polarity of a uxin transport. We outline the epitope tagging strategy being used in our l aboratory to immunolocalize AUX1 and discuss the implications of its subcel lular localization for auxin redistribution within root apical tissues. Las tly, we describe a novel carrier-based mechanism that plant cells might use to determine their relative position(s) within an auxin gradient, drawing parallels with the mechanism of glucose perception in yeast.