Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/1996
Publication Date: N/A
Interpretive Summary: Large areas of land within the U.S. and a significant proportion of the world s arable lands are acidic. In these acid soils, aluminum (Al) toxicity is the primary factor limiting crop production. There is considerable genetic variation in sensitivity to Al between different plant species and genotypes, yet the genetic and molecular basis for Al tolerance eis still poorly understood. In this study, we screened mutagenized populations of Arabidopsis thaliana and isolated a family of mutants that exhibited increased sensitivity to Al toxicity. Arabidopsis is a model plant system for molecular and genetic research. We showed that at least 8 different recessive genes conferred Al sensitivity. In some cases this sensitivity was due to an increased root accumulation of toxic Al ions, while in other mutants toxicity was observed even though the roots did not accumulate large amounts of Al. The significance of these findings are that tthey provide information about the genetic complexity of Al toxicity, and set the stage for future work aimed at cloning the genes associated with Al toxicity. The cloning of these genes should greatly increase our chances of altering or introducing genes into crop plants that confer an increased ability for those plants to grow on acidic, Al toxic soils.
Technical Abstract: Aluminum-resistant (alr) mutants of Arabidopsis were isolated and characterized in order to gain a better understanding of genetic and physiological mechanisms of Al resistance, and to begin a program to isolate genes that confer Al resistance via map-based cloning procedures. The alr mutants were identified on the basis of enhanced root growth in the epresence of levels of Al that strongly inhibited root growth in wild type seedlings. Based on genetic analysis of the alr mutants, Al resistance was shown to be a semidominant trait, and chromosome mapping of the mutants with microsatellite and RAPD markers indicated that the mutants mapped to one of two loci on chromosome 1 (alr-108, alr-128, alr-131, alr-139) or chromosome 4 (alr-104). All of the mutants that mapped together on chromosome 1 exhibited increased release of citrate or malate (as well as pyruvate) compared with wild type, suggesting that Al exclusion from roots of these alr mutants involves enhanced organic acid exudation. This study represents the first report of Arabidopsis mutants selected for increased Al resistance in roots. Isolation of these alr mutants will allow for further characterization of Al-resistance mechanisms and may provide an opportunity to identify other Al-resistance mechanisms that have not been previously described. In addition, we now have the opportunity to isolate genes responsible for the Al resistance traits exhibited by these alr mutants.