ARS | Publication request: Positional Cloning and Characterization of AltSB, a Major Aluminum Tolerance Gene in Sorghum: Toward the Identification of the Molecular and Physiological basis of Allelic effects

Submitted to: Plant and Animal Genome VX Conference Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: December 11, 2006
Publication Date: January 13, 2007
Citation: Magalhaes, J., Liu, J., Alves, V., Guimaraes, C., Wang, Y., Lana, U., Schaffert, R., Hoekenga, O., Klein, P., Kochian, L.V. 2007. Positional Cloning and Characterization of AltSB, a Major Aluminum Tolerance Gene in Sorghum: Toward the Identification of the Molecular and Physiological basis of Allelic effects[abstract]. Plant and Animal Genome VX Conference Abstracts. p. 58.

Technical Abstract: Aluminum toxicity is a major constraint for agriculture on acid soils, which comprise over half of the world’s potentially arable lands. However, the molecular basis underlying the most accepted tolerance mechanism based on Al-induced organic acid release by root apices, is only now being elucidated. A single major Al tolerance gene, AltSB, was mapped to the end region of sorghum chromosome 3. Subsequently, high-resolution mapping allowed us to define a target region of 25 Kbp containing three ORFs. One of these ORFs (ORF7) corresponds to a member of a family of membrane transporters previously implicated with the efflux of low molecular weight solutes. The following evidences indicate that this gene corresponds to AltSB: (i) among all three ORFs, ORF7 is the only one expressed in sorghum root apices. (ii) ORF7 is expressed at high levels only in a tolerant near-isogenic line for AltSB and expression is inducible over time of exposure to Al, which is consistent with the pattern of citrate release. (iii) ORF7 expression in transgenic Arabidopsis conferred increased Al tolerance and Al-induced citrate release. Sequence scanning of 25 Kbp region indicated that allelic effects on the phenotype are controlled by polymorphisms on regulatory regions, which primarily affect gene expression. Interestingly, a MITE insertion in the promoter region was found to be highly variable in size and correlated with Al tolerance across members of a sorghum diversity panel. The allelic basis for differences in Al tolerance is now under investigation by association analysis on a diverse sorghum core collection.