Submitted to: Plant and Animal Genome Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: January 17, 1999
Publication Date: N/A
Technical Abstract: The recent cloning of plant disease resistance genes has allowed similar sequences to be cloned using degenerate PCR primers that recognize conserved regions of the previously cloned genes. Analyses of several resistance gene analogs (RGAs) from wheat separated them into four classes. Primers were designed to unique regions that allowed specific amplification nof each wheat RGA class. Although previous analyses revealed a lack of synteny among RGAs from cereal species using degenerate primers, the conservation of specific RGA classes has not been tested. Therefore, the specific RGA primers were used to amplify DNA from a diverse group of plant species to test the evolutionary conservation of each RGA class from wheat. Two monocots (wheat, taro), two dicots (lima bean, four o clocks), a cycad and a clubmoss were tested. Three of the four wheat RGAs were present in at least one other plant species. Sequences of the test species plus others with high BLAST scores from GenBank were aligned using ClustalX and a phylogenetic analysis was performed with PHYLIP. These analyses revealed that each RGA class formed a distinct cluster with high evolutionary conservation. In addition to wheat, RGA class 4 also was present in both dicot species, while classes 1 and 2 were present in most of the species tested, including the cycad and clubmoss. The apparent high evolutionary conservation of these RGA sequences from wheat probably means that they evolved in early land plants and have been maintained over time by selection. Such a pattern may be expected if the RGAs encode resistance against pathogens or potential pathogens encountered commonly by all plant species. Therefore, high evolutionary conservation may result by descent from a common ancestor and may occur often among RGA sequences from plants.