Comparative mapping of a major aluminum tolerance gene in sorghum and other species in the Poaceae

In several crop species within the Triticeae tribe of the grass family Poaceae, single major aluminum (Al) tolerance genes have been identified that effectively mitigate Al toxicity, a major abiotic constraint to crop production on acidic soils. However, the trait is quantitatively inherited in species within other tribes, and the possible ancestral relationships between major Al tolerance genes and QTL in the grasses remain unresolved. To help establish these relationships, we conducted a molecular genetic analysis of Al tolerance in sorghum and integrated our findings with those from previous studies performed in crop species belonging to different grass tribes. A single locus, Alt(SB), was found to control Al tolerance in two highly Al tolerant sorghum cultivars. Significant macrosynteny between sorghum and the Triticeae was observed for molecular markers closely linked to putatively orthologous Al tolerance loci present in the group 4 chromosomes of wheat, barley, and rye. However, Alt(SB) was not located within the homeologous region of sorghum but rather mapped near the end of sorghum chromosome 3. Thus, Alt(SB) not only is the first major Al tolerance gene mapped in a grass species that does not belong to the Triticeae, but also appears to be different from the major Al tolerance locus in the Triticeac. Intertribe map comparisons suggest that a major Al tolerance QTL on rice chromosome 1 is likely to be orthologous to Alt(SB), whereas another rice QTL on chromosome 3 is likely to correspond to the Triticeae group 4 Al tolerance locus. Therefore, this Study demonstrates a clear evolutionary link between genes and QTL encoding the same trait in distantly related species within a single plant family.