AUX1 regulates root gravitropism in Arabidopsis by facilitating auxin uptake within root apical tissues

Abstract

Plants employ a specialized transport system composed of separate influx and efflux carriers to mobilize the plant hormone auxin between its site(s) of synthesis and action. Mutations within the permease-like AUX1 protein significantly reduce the rate of carrier-mediated auxin uptake within Arabidopsis roots, conferring an agravitropic phenotype. We are able to bypass the defect within auxin uptake and restore the gravitropic root phenotype of aux1 by growing mutant seedlings in the presence of the membrane-permeable synthetic auxin, 1-naphthaleneacetic acid. We illustrate that AUX1 expression overlaps that previously described for the auxin efflux carrier, AtPIN2, using transgenic lines expressing an AUX1 promoter::uidA (GUS) gene. Finally, we demonstrate that AUX1 regulates gravitropic curvature by acting in unison with the auxin efflux carrier to co-ordinate the localized redistribution of auxin within the Arabidopsis root apex. Our results provide the first example of a developmental role for the auxin influx carrier within higher plants and supply new insight into the molecular basis of gravitropic signalling.

Isolation, Characterization, and Pericycle-Specific Transcriptome Analyses of the Novel Maize Lateral and Seminal Root Initiation Mutant rum1

“…Experiments with auxin transport inhibitors in Arabidopsis have demonstrated that the auxin movement from the shoot toward the root tip is responsible for lateral root development (Reed et al, 1998), while auxin movement away from the root tip is required for gravitropism and primary root elongation (Rashotte et al, 2000), although involvement of basipetal auxin transport in lateral root formation has also been discussed recently (Casimiro et al, 2001). Several genes involved in auxin transport, including the postulated efflux carriers of the pin family (Gälweiler et al, 1998;Mü ller et al, 1998;Friml et al, 2002aFriml et al, , 2002b, the auxin importer aux1 (Marchant et al, 1999), and the postulated efflux carriers pgp1, pgp2, and pgp19 (Noh et al, 2001), have been cloned recently in Arabidopsis. The maize ortholog of pgp1 is not expressed in roots (Multani et al, 2003).…”

Do volatile compounds produced by Fusarium oxysporum and Verticillium dahliae affect stress tolerance in plants?

“…It was reported that under high salt, the inhibition of lateral root formation is caused by suppression of basipetal auxin transport, resulting in over-accumulation of auxin in root epidermis of elongation zone while depleting auxin in root apex (Wang et al 2009). AUX1 encodes a non-redundant auxin influx carrier (Marchant 1999), which facilitates auxin distribution in lateral root cap and elongation of epidermal cells (Marchant et al 2002; Band et al 2014). The aux1-7 mutant exhibited higher susceptibility to salt stress than the wild type, suggesting that auxin transport is required for alleviating salt stress (Wang et al 2009; Galvan-Ampudia and Testerink 2011).…”

Auxin Polar Transport and Automorphosis in Plants

“…The influx of dissociated auxin anion (IAA -) together with 2H + from apoplast to cytoplasm is mediated by a family of amino acid permease-like proton-gradientdriven transporter proteins, AUX1//LAX, located in an anti-polar side of plasma membrane, whereas partially IAA also moves passively via lipophilic diffusion (Bennette et al, 1996;Marchant et al, 1999;Swarup et al, 2001). Thus, AUX1 is possible to be involved in both regulation of gravitropism in roots and auxin influx as carrier proteins.…”