ALS3 encodes a phloem‐localized ABC transporter‐like protein that is required for aluminum tolerance in Arabidopsis

Abstract

Aluminum (Al) toxicity in acid soils is a worldwide agricultural problem that severely limits crop productivity through inhibition of root growth. Previously, Arabidopsis mutants with increased Al sensitivity were isolated in order to identify genes important for Al tolerance in plants. One mutant, als3, exhibited extreme root growth inhibition in the presence of Al, suggesting that this mutation negatively impacts a gene required for Al tolerance. Map-based cloning of the als3-1 mutation resulted in the isolation of a novel gene that encodes a previously undescribed ABC transporter-like protein, which is highly homologous to a putative bacterial metal resistance protein, ybbM. Northern analysis for ALS3 expression revealed that it is found in all organs examined, which is consistent with the global nature of Al sensitivity displayed by als3, and that expression increases in roots following Al treatment. Based on GUS fusion and in situ hybridization analyses, ALS3 is primarily expressed in leaf hydathodes and the phloem throughout the plant, along with the root cortex following Al treatment. Immunolocalization indicates that ALS3 predominantly accumulates in the plasma membrane of cells that express ALS3. From our results, it appears that ALS3 encodes an ABC transporter-like protein that is required for Al resistance/tolerance and may function to redistribute accumulated Al away from sensitive tissues in order to protect the growing root from the toxic effects of Al.

Fluorescence Resonance Energy Transfer-Sensitized Emission of Yellow Cameleon 3.60 Reveals Root Zone-Specific Calcium Signatures in Arabidopsis in Response to Aluminum and Other Trivalent Cations

“…This notion is further supported by the fact that alr104 and als3-1 mutants, which were previously shown to be resistant and sensitive to Al 3+ , respectively (Larsen et al, 1998(Larsen et al, , 2005, displayed the same [Ca 2+ ] cyt responses to all three trivalent cations as wild-type seedlings (Fig. 9).…”

“…NPPB alone did not evoke any [Ca 2+ ] cyt changes in the root transition zone (Fig. 8G Larsen et al, 1998) and one Al 3+ -sensitive mutant (als3-1; Larsen et al, 2005) with the YC3.60 reporter and evaluated the [Ca 2+ ] cyt response after treatment with Al 3+ , La 3+ , or Gd 3+ . We again focused our imaging on the region of the root that exhibited the biphasic [Ca 2+ ] cyt response, since this pattern of [Ca 2+ ] cyt change appears to be the most distinguishing and common feature of the trivalent cation response.…”

“…Here (Larsen et al, 1998) and the Al 3+ -sensitive mutant als3-1 (Larsen et al, 2005), indicating that the early [Ca 2+ ] cyt increases we report here may not be tightly linked to mechanisms of Al 3+ toxicity but rather to a general trivalent cation response. Our study further shows that FRETsensitized emission imaging of Arabidopsis roots expressing YC3.60 provides a robust method for documenting [Ca 2+ ] cyt signatures in different root developmental zones that should be useful for future studies on Ca 2+ signaling mechanisms in plants.…”

Coordination between Apoplastic and Symplastic Detoxification Confers Plant Aluminum Resistance

“…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.…”