Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/31/2006
Publication Date: 6/20/2006
Citation: Hoekenga, O., Maron, L.G., Pineros, M.A., Cancado, G.M., Shaff, J., Kobayashi, Y., Ryan, P.R., Dong, B., Delhaize, E., Sasaki, T., Matsumoto, H., Koyama, H., Kochian, L.V. 2006. Atalmt1 (at1g08430) is a novel, essential factor for aluminum tolerance in arabidopsis thaliana and encodes an aluminum-activated malate transporter. Proceedings of the National Academy of Sciences. 103:9738-9743. Interpretive Summary: Large areas of land within the U.S. and over 40% of the world’s arable lands are acidic. In these acid soils, aluminum (Al) toxicity is the primary factor limiting crop production via Al-induced inhibition of root growth. The physiological and molecular basis for Al tolerance is still poorly understood. Thus, we need a more complete understanding of the mechanisms underlying Al tolerance if we are going to be able to develop more Al tolerant crop plants for improved cultivation on acid soils. In this paper, we used molecular, genetic, and physiological methods to study Al tolerance in the model plant species, Arabidopsis. We investigated the role of a gene that was a close relative of a recently identified wheat Al tolerance gene, ALMT1, in Arabidopsis Al tolerance. We showed that the related Arabidopsis gene encoded a transport protein that is the Al-activated malate efflux transporter that is critical for Arabidopsis Al tolerance. However, we also found that this gene does not vary in different lines of Arabidopsis that differ widely in Al tolerance. These findings show that this gene plays a key role in Arabidopsis Al tolerance but does not explain the genetic variation for this trait in Arabidopsis. These findings are important, as they indicate that there must be a novel gene that possibly interacts with this malate transporter and is responsible for the genetic variation for Al tolerance in different lines of Arabidopsis.
Technical Abstract: Aluminum (Al) tolerance in Arabidopsis is a genetically complex trait yet is mediated by a single physiological mechanism based on Al-activated root malate efflux. We investigated a possible molecular determinant for Arabidopsis Al tolerance involving a homolog of the wheat Al-activated malate transporter, ALMT1. This gene, named AtALMT1, was found within the primary confidence interval for a major Al tolerance quantitative trait locus (QTL) we identified on chromosome 1 using a Landsberg erecta (Ler) x Columbia (Col) population (Hoekenga et al. 2003). Physiological analysis of a T-DNA knockout mutant (MT) 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 Col, sensitive 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 between these ecotypes. Physiological analysis of F1 individuals from a cross of AtALMT1 MT (Col) with WT Ler 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 this QTL on chromosome 1 indicated that AtALMT1 is located proximal to the QTL. These results indicate that AtALMT1 is a novel, essential factor for Al tolerance in Arabidopsis but does not represent the major Al tolerance QTL also found on chromosome 1.