2007 Annual Report 1a.Objectives (from AD-416) The proposed work will build upon our recent cloning of ALTSB, the primary Al tolerance gene in sorghum and will involve the following objectives:. 1)Functional complementation analysis via expression of the candidate ALTSB gene in transgenic sorghum, maize and Arabidopsis;. 2)Promoter analysis, including identification of Al responsive elements and promoter regions responsible for the increased expression. 3)Identification of proteins that interact with and regulate ALTSB. 1b.Approach (from AD-416) The approaches will involve techniques from biotechnology, molecular biology and protein biochemistry. Agrobacterium-mediated stable plant transformation involving the floral dip method and transformation of embryogenic calli followed by plant regeneration will be used to develop transgenic plants expressing the tolerant AltSB allele. Transient expression of AltSB promoter::reporter gene constructs in sorghum root protoplasts will be used to study cis-acting factors responsible for Al-inducible and enhanced expression in root tips of tolerant plants. Spli-ubiquitin yeast two-hybrid assays will be used to identify proteins that interact with the ALTSB transport protein. 3.Progress Report This report documents research conducted under a reimbursable agreement between ARS and CSREES via the National Research Initiative Competitive Grants Program. Additional details of research can be found in the report for the in-house associated project 1907-21000-024-00D “Genomic approaches to improving transport and detoxification of selected mineral elements in crop plants”. Progress for this project involved characterization of the expression of the sorghum Al tolerance gene, AltSB, as well as characterization of the diversity in gene sequence and function for this gene in different sorghum lines.