AtALMT1 , which encodes a malate transporter, is identified as one of several genes critical for aluminum tolerance in Arabidopsis

Abstract

Aluminum (Al) tolerance in Arabidopsis is a genetically complex trait, yet it is mediated by a single physiological mechanism based on Al-activated root malate efflux. We investigated a possible molecular determinant for Al tolerance involving a homolog of the wheat Al-activated malate transporter, ALMT1. This gene, named AtALMT1 (At1g08430), was the best candidate from the 14-member AtALMT family to be involved with Al tolerance based on expression patterns and genomic location. Physiological analysis of a transferred DNA knockout mutant for AtALMT1 as well as electrophysiological examination of the protein expressed in Xenopus oocytes showed that AtALMT1 is critical for Arabidopsis Al tolerance and encodes the Al-activated root malate efflux transporter associated with tolerance. However, gene expression and sequence analysis of AtALMT1 alleles from tolerant Columbia (Col), sensitive Landsberg erecta (Ler), and other ecotypes that varied in Al tolerance suggested that variation observed at AtALMT1 is not correlated with the differences observed in Al tolerance among these ecotypes. Genetic complementation experiments indicated that the Ler allele of AtALMT1 is equally effective as the Col allele in conferring Al tolerance and Al-activated malate release. Finally, fine-scale mapping of a quantitative trait locus (QTL) for Al tolerance on chromosome 1 indicated that AtALMT1 is located proximal to this QTL. These results indicate that AtALMT1 is an essential factor for Al tolerance in Arabidopsis but does not represent the major Al tolerance QTL also found on chromosome 1. abiotic stress ͉ electrophysiology ͉ genetics ͉ organic acid exudation

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

“…This demonstrates some specificity of the wheat and B. napus proteins for malate over citrate and indicates that in the absence of supplementation the endogenous malate concentration in oocytes is too low to generate large currents. Smaller currents were also detected in oocytes expressing AtALMT1 in the absence of Al 3+ [17] which contrasts with the strict requirement for Al 3+ to activate malate efflux in wild type plants. Oocytes expressing the BnALMT genes generate larger currents than oocytes expressing either TaALMT1 or AtALMT1 but this may reflect experimental differences (e.g.…”

“…Differences in Al 3+ resistance between the two Arabidopsis thaliana accessions Columbia (Al 3+ -resistant) and Landsberg (Al 3+ -sensitive) can be attributed to differences in Al 3+ -activated malate efflux and several QTLs contribute to the phenotype [16]. A gene (AtALMT1; At1g08430) encoding a TaALMT1-like protein is located within an Al 3+ resistance QTL located on chromosome 1 [17]. Although AtALMT1 is only 44% identical to TaALMT1 it appears to function in a similar way.…”

“…Although AtALMT1 is only 44% identical to TaALMT1 it appears to function in a similar way. Al 3+ not only activates AtALMT1 to trigger malate efflux but is also required to induce AtALMT1 expression ( [17,18]; Fig. 2).…”

“…According to this definition the ALMT family consists entirely of plant proteins. The protein encoded by AtALMT11 (At4g17585) of Arabidopsis was originally included as a member of the ALMT family [17] but is excluded here because it is predicted to be soluble. A phylogenetic tree of all known full length ALMT members is shown in Fig.…”

The vacuolar channel VvALMT9 mediates malate and tartrate accumulation in berries of Vitis vinifera

“…Clade I, to which AtALMT1 (Hoekenga et al 2006) belongs, contains in V. vinifera 8 members while it includes 5 members in A. thaliana. Clade II is represented in V.…”