Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2008
Publication Date: 5/1/2008
Citation: Collins, N., Shirley, N.J., Saeed, M., Pallotta, M., Gustafson, J.P. 2008. An ALMT1 gene cluster controlling aluminium (aluminum) tolerance at the Alt4 locus of rye (Secale cereale L.). Genetics. 179(1):669-682. Interpretive Summary: The most abundant metal on earth is aluminium, which is highly toxic to plant growth and is found in about 2.5 billion hectares of acid soils worldwide. Many of the world’s farmers living on acid soils do not have the management options required to improve cereal production. Therefore, the development of cereal cultivars capable of improved production on acid soils is needed. Cultivated rye, the world’s most acid soil tolerant cereal, contains an enormous diversity in organization of gene complexes, which play a role in controlling aluminum tolerance. An important question concerns the nature of these gene complexes and how they influence rye production on acid soils? An experiment was designed to characterize the presence of malate transporter (ALMT) genes thought to contribute to the up-regulation of aluminum tolerance expression in rye. Rye mapping populations were created and analyzed for the presence or absence of ALMT genes, which involved an analysis of rye aluminium tolerance by growing seedlings in a hydroponic solution containing aluminium and measuring root growth. The results showed that there is variation in copy number and chromosome location of ALMT genes in rye. At least two ALMT gene complexes were characterized that varied in gene copy number and expression of rye aluminum tolerance. A number of DNA sequence inserts and deletions within the ALMT gene complexes were identified. The two types of rye ALMT gene complexes characterized in the present study add to our understanding of the expression of aluminum tolerance in rye, and impact on the ability of rye to grow on acid soils.
Technical Abstract: Aluminium toxicity is a major problem in agriculture worldwide. Among the cultivated triticeae, rye (Secale cereale L.) is one of the most Al-tolerant and represents an important potential source of Al-tolerance for improvement of wheat. The Alt4 Al-tolerance locus of rye contains a cluster of genes homologous to the single-copy Al-activated malate transporter (TaALMT1) Al-tolerance gene of wheat. Tolerant (M39A-1-6) and intolerant (M77A-1) rye haplotypes contain five and two genes respectively, of which two (ScALMT1-M39.1 and ScALMT1-M39.2) and one (ScALMT1-M77.1) are highly expressed in the root tip, the main site of Al-tolerance/susceptibility. All three transcripts are induced by exposure to Al. High-resolution genetic mapping identified two resistant lines resulting from recombination within the gene cluster. These recombinants exclude genes flanking the gene cluster as candidates for controlling Alt4 tolerance, including a homologue of the barley HvMATE Al-tolerance gene. In the recombinants, one hybrid gene containing a chimeric open reading frame, and the ScALMT1-M39.1 gene, each appeared to be sufficient to provide full tolerance. mRNA splice variation was observed for two of the rye ALMT1 genes, and in one gene was correlated with a ~400 bp insertion in one of its introns.