Submitted to: Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/15/2004
Publication Date: 8/1/2004
Citation: Magalhaes, J., Garvin, D.F., Sorrells, M., Klein, P., Schaffert, R., Wang, Y., Li, L., Kochian, L.V. 2004. Comparative mapping of altsb, a novel aluminum tolerance gene in sorghum bicolor (l.) moench, reveals inter-tribe synteny among al tolerance genes in the poaceae. Genetics. 167:53-63. 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. There is considerable genetic variation in tolerance to Al between different plant species and genotypes, yet the molecular, genetic, and physiological basis for Al tolerance is still poorly understood. Thus, we need a more complete understanding of the genetic and mechanistic basis for Al tolerance if we are going to be able to develop more Al tolerant crop plants for improved cultivation on acid soils. One strategy for improving crop Al tolerance is to isolate genes conferring tolerance, and characterize these genes to understand their function. Also, these genes could be an important resource for improving crop Al tolerance via biotechnology. In this paper, we characterized the genetics of Al tolerance in sorghum, a cereal crop species that is becoming a model system for molecular and genetic research. We showed that Al tolerance is controlled by a single gene, and markers closely linked to this gene were generated which allowed us to determine that the Al tolerance locus is at the end of chromosome 3. This has set the stage for current efforts to clone this gene via fine-scale molecular mapping.
Technical Abstract: When soil pH declines below pH 5, aluminum (Al) is released into the soil solution in ionic forms that are highly toxic to plant roots. Because of the widespread extent of acid soils, Al toxicity is a major constraint to crop production worldwide. Thus, there is considerable interest in elucidating Al tolerance mechanisms and associated genes in crop species. A molecular genetic analysis of Al tolerance was conducted using the international standard for Al tolerance in sorghum, SC283, and conservation of tolerance genes across domesticated grasses was examined by comparative molecular mapping. Al tolerance in SC283 was conferred by a single partially-dominant gene, which was designated Altsb. This same gene was also found to condition Al tolerance in another highly tolerant cultivar SC566. While the position and order of molecular markers in close proximity to the putatively orthologous Al tolerance genes Altbh in wheat, Alp in barley, and Alt3 in rye were found to be conserved in sorghum, Altsb was located in a different region, near the end of sorghum chromosome 3. Since sorghum chromosome 3 is not homoeologous to the Triticeae group 4 chromosomes that harbor Altbh, Alp and Alt3, Altsb does not appear to be orthologous to the major Al tolerance genes described to date in the Triticeae. Results from comparative mapping suggest that different Al tolerance genes operating in the Triticeae and the Andropogoneae are likely to correspond to two major Al tolerance QTLs in rice, a member of the Oryzeae tribe.