Advances in the Biological Functions of Auxin Transporters in Rice

Auxin is the earliest discovered plant hormone, which plays important roles in each aspect of plant growth and development. There are two main pathways for auxin to be transported from the synthetic site (such as young leaves and terminal buds) to the active site. First, auxin is transported over long distances through phloem in an unfixed direction throughout the whole plant. Second, short-distance polar transport between cells requires the participation of auxin carriers, including unidirectional transport from stem tip to root and local unidirectional transport between tissues. Polar transport is critical to the establishment and maintenance of the auxin concentration gradient, which specifically regulates plant growth and development and responds to environmental changes. In this article, we reviewed the research progress of auxin transporters AUX1/LAX, PIN, and ABCB families, and some potential auxin transporters in rice growth and development, which provide information for the interpretation of biological functions of polar auxin transport families and lay a foundation for the genetic improvement of important agronomic traits in rice.