Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/1/1998
Publication Date: N/A
Citation: 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. There is considerable genetic variation in sensitivity to Al between different plant species and genotypes, yet the genetic and molecular basis for Al tolerance is still poorly understood. We need a more complete understanding of the molecular genetics of Al toxicity and tolerance if we are going to be able to develop more Al resistant crop plants. In order to increase our understanding of this topic, we have screened mutagenized populations of Arabidopsis thaliana (a model plant system for molecular and genetic research) and isolated 5 Al tolerant mutants. In this study, we have characterized the genetics and physiology of these mutants and showed that Al tolerance in these mutants was controlled by 2 different genes (on chromosomes 1 and 4). .Both genes are involved in preventing Al from accumulating in the root tip The gene on chromosome 1 controls the release of organic acids that can bind Al and keep it out of the root, while the gene on chromosome 4 is involved in maintaining a higher pH around the root tip, which lowers the concentration of the toxic Al ion. These results are significant in that they clearly show that two different genes control two distinct mechanisms of Al tolerance. Also, we now will be able to clone these genes, which possibly can then be used to generate transgenic crop plants with increased Al tolerance.
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 indicated that the mutants mapped to one of two loci on chromosome 1 or chromosome 4. It was found that each category of mutants accumulated lower levels of Al in the root tips compared with wild type. 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 lexclusion from roots of these alr mutants involves enhanced organic acid exudation. Roots of alr-104, on the other hand, did not exhibit increased release of malate or citrate, but did mediate a moderate increase in the pH of the nutrient solution bathing the roots. Isolation of these alr mutant 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.