Acts as a component of the auxin efflux carrier. Seems to be involved in the polar auxin transport which may promote adventitious root emergence and control tillering. Expressed in vascular tissues of root, stem and leaf. Expressed in anthers, embryo and in the primordia of adventitious and lateral roots (PubMed:16085936). Expressed in roots, stem bases, stems, leaves and young panicles (PubMed:19825657). Plants silencing PIN1A exhibit inhibition of the emergence and development of adventitious roots, increased number of tillers and enlarged tiller angles. Belongs to the auxin efflux carrier (TC 2.A.69.1) family.