PGP4, an ATP Binding Cassette P-Glycoprotein, Catalyzes Auxin Transport in Arabidopsis thaliana Roots

Abstract

Members of the ABC (for ATP binding cassette) superfamily of integral membrane transporters function in cellular detoxification, cell-to-cell signaling, and channel regulation. More recently, members of the multidrug resistance P-glycoprotein (MDR/PGP) subfamily of ABC transporters have been shown to function in the transport of the phytohormone auxin in both monocots and dicots. Here, we report that the Arabidopsis thaliana MDR/PGP PGP4 functions in the basipetal redirection of auxin from the root tip. Reporter gene studies showed that PGP4 was strongly expressed in root cap and epidermal cells. PGP4 exhibits apolar plasma membrane localization in the root cap and polar localization in tissues above. Root gravitropic bending and elongation as well as lateral root formation were reduced in pgp4 mutants compared with the wild type. pgp4 exhibited reduced basipetal auxin transport in roots and a small decrease in shoot-to-root transport consistent with a partial loss of the redirective auxin sink in the root. Seedlings overexpressing PGP4 exhibited increased shoot-to-root auxin transport. Heterologous expression of PGP4 in mammalian cells resulted in 1-N-naphthylthalamic acid-reversible net uptake of [ 3 H]indole-3-acetic acid. These results indicate that PGP4 functions primarily in the uptake of redirected or newly synthesized auxin in epidermal root cells.

Master and servant: Regulation of auxin transporters by FKBPs and cyclophilins

“…Members of plasma membrane located AUX1/LAX family are grouped as auxin importers [24]. Auxin exporters are primarily represented by plasma membrane localized PINs (so-called long PINs, see below) and members of the ABCB family, which have so far all been found to be plasma membrane-embedded [6,[25][26][27]. However, it should be mentioned that recently ABCB4 and ABCB21 were characterized as facultative importer/exporters whose transport directionality seems to be triggered by intracellular auxin levels [28].…”

“…Recent analyses in heterologous, non-plant auxin-transport systems (such as yeast, HeLa cells and Xenopus oocytes) demonstrated that AUX1/LAX influx, and ABCB and PIN-mediated IAA efflux activity is substrate-specific and rate limiting [6,19,25,26,[37][38][39][40][41][42], providing experimental evidence that these proteins are bona fide auxin transporters. Although plant ABCBs belong to the large superfamily of multidrug resistance transporters, they were found to own a high degree of substrate specificity toward only a few auxinic compounds but not to transport closely related substances (such as the anti-auxin 2-NAA or benzoic acid [6]) or classical substrates of mammalian ABCBs (such as rhodamin123, daunomycin and vinblastine [43]).…”

The Contribution of Transposable Elements to Expressed Coding Sequence in Arabidopsis thaliana

“…These 162 genes remain expressed, and at least several are functionally well characterized: for example, DET3 (At1g12840) (Schumacher et al 1999), PGP4 (At2g47000) (Terasaka et al 2005), and HYD1 (At1g20050) (Topping et al 1997). Of the 2373 ''TE genes,'' 125 were annotated as alternatively spliced.…”

ARL2, ARG1 and PIN3 define a gravity signal transduction pathway in root statocytes

“…The development of auxin asymmetry is thought to derive from redirection of auxin through the root tip toward the new lower flank of the root cap, followed by basipetal transport to the elongation zone (Blancaflor and Masson, 2003;Swarup et al, 2005). Basipetal transport of auxin from the cap to the elongation zone requires both auxin influx and efflux carriers, encoded by AUX1 and AGR1/PIN2/EIR1/WAV6, respectively (reviewed in Chen et al, 1999;Swarup et al, 2005), and members of the MDR/PGP ABC transporter families (Geisler and Murphy, 2006;Lewis et al, 2007;Lin and Wang, 2005;Terasaka et al, 2005). Basipetal auxin transport may also be regulated by molecules affecting the activity, expression and subcellular localization of auxin transporters in the lateral cell files of the root (as reviewed by Muday and Rahman, 2007).…”