The function of ABCB transporters in auxin transport

Abstract

Plant ATP-binding cassette (ABC) transporters consist of largest family members among many other membrane transporters and have been implicated in various functions such as detoxification, disease resistance and transport of diverse substrates. Of the ABC-B/multi-drug resistance/P-glycoprotein (ABCB/MDR/PGP) subfamily, at least five members have been reported to mediate cellular transport of auxin or auxin derivatives. Although single mutant phenotypes of these genes are milder than PIN-FORMED (PIN) mutants, those ABCBs significantly contribute for the directional auxin movement in the tissue-level auxin-transporting assay. Uniformly localized ABCB proteins in the plasma membrane (PM) are generaly found in different plant species and stably retained regardless of internal and external signals. This implies that these ABCB proteins may play as basal auxin transporters.

Keywords: ABCB; Arabidopsis; PGP; PIN; auxin transporter; non-polar localization; sterol.

Figure 1. Expression and contribution of ABCB proteins for the polar auxin transport.

Figure 2. Distinctive functions between ABCBs and PINs in auxin transport. ABCBs, localizing stably and symmetrically in the PM, function as basal auxin transporters and regulate cellular auxin homeostasis. In contrast, PINs, asymmetrically localized and with distribution dynamicity in response to developmental and environmental cues, mediate directional auxin transport to raise formative local auxin gradients.