Arabidopsis ALS1 encodes a root tip and stele localized half type ABC transporter required for root growth in an aluminum toxic environment

Abstract

Aluminum toxicity in acid soils severely limits crop productivity through inhibition of root growth and, consequently, shoot development. Several Arabidopsis mutants were previously identified as having roots with Al hypersensitivity, suggesting that these represent deleterious mutations affecting genes required for either Al tolerance or resistance mechanisms. For this report, the als1-1 mutant was chosen for further characterization. The phenotype of als1-1 is most obviously presented in Al challenged roots, as evidenced by exaggerated root growth inhibition in conjunction with increased expression of Al-responsive genes compared to wt. Using a map-based cloning approach, the als1-1 mutation was isolated and found to represent a deleterious amino acid substitution in a previously uncharacterized half type ABC transporter, At5g39040, which is expressed in a non-Al dependent manner in all organs tested. GUS-dependent analyses revealed that ALS1 expression is primarily localized to the root tip and the vasculature throughout the plant. Concomitant with this, an ALS1: GFP fusion accumulates at the vacuolar membrane of root cells, indicating that ALS1 may be important for intracellular movement of some substrate, possibly chelated Al, as part of a mechanism of Al sequestration.

Coordination between Apoplastic and Symplastic Detoxification Confers Plant Aluminum Resistance

“…Although ALS1 expression was not aluminum inducible (Fig. 5), in accordance with Larsen et al (2007), root ALS1 expression was about 50% lower in yucca and the wild type treated with exogenous NAA than in the wild type (Fig. 5) but was about 50% higher than the wild type in xth15 under control conditions (Fig.…”

“…ALS1 is reported to be a root tip tonoplast transporter and responsible for aluminum redistribution between the cytoplasm and vacuole (Larsen et al, 2007). To determine whether differential expression abundance of ALS1, predicted to correlate with function levels, could underlie the differential sensitivity of yucca and xth15, we monitored ALS1 expression in roots with and without aluminum stress.…”

“…Recently, some transporters involved in the aluminum distribution within cells have been identified. In Arabidopsis (Arabidopsis thaliana), the tonoplast-localized ATP-binding cassette (ABC) transporter Al sensitive1 (ALS1), which is involved in Al tolerance in Arabidopsis (Larsen et al, 2007), while ALS3 is responsible for movement of aluminum away from sensitive tissues for sequestration in more tolerant tissues (Larsen et al, 2005(Larsen et al, , 2007. Huang et al (2012) identified a rice (Oryza sativa) tonoplast-localized aluminum transporter, encoded by OsALS1, which is responsible for sequestration of aluminum into vacuoles and thus contributes to the internal detoxification of aluminum in rice.…”

The roles of organic anion permeases in aluminium resistance and mineral nutrition

“…Two Al 3+ -sensitive mutants of Arabidopsis (als1 and als3) are mutated in genes that encode proteins of the ABC transporter family [35,36]. The functions and substrates of ALS1 and ALS3 are not known but from the mutant phenotypes, Larsen et al [35,36] inferred that the proteins act to mobilise and sequester Al 3+ within the plant to confer tolerance. ALS1 is located at the tonoplast and the gene is expressed primarily in root apices and the vascular system.…”

“…In some plant species Al 3+ can be either mobilised or stored when complexed by organic anions (see [3]) but to date the transport proteins that mediate these processes are unknown. An intriguing possibility is that ALS1 and ALS3 are involved in these processes and capable of transporting Al 3+ chelated to small peptides [35] or organic anions such as oxalate and citrate.…”