Weblog – Summary of
"Functional variation in a disease resistance gene in populations of Arabidopsis thaliana"
The paper was authored by T. H. Jorgensen and B. C. Emerson of the Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich, England, and was published in the journal Molecular Ecology (2008) 17, 4912-4923.
The authors investigated whether the molecular diversity in RPW8 (Recognition of Powdery Mildew), a gene conferring broad-spectrum resistance to powdery mildews in Arabidopsis thaliana, arose through selection or a random process such as genetic drift. To do this, initially, they investigated whether local populations of A. thaliana were genetically variable by analysing variation at microsatellite loci within their test populations. Secondly, they determined if molecular variation present at RPW8 can explain natural variation in powdery mildew resistance. Thirdly, they related within- and between-population variation at RPW8 with that of neutral satellite markers to provide a test for the presence of selection.
The authors took seeds from eight populations of A. thaliana from locations in England, situated from 2-115 km apart. The populations were from areas of low anthropogenic disturbance. The seeds were germinated and the plants grown under identical conditions within the laboratory. The plants were then inoculated with powdery mildew and inspected for signs of infection at 7 and 14 days. Plants were grouped as susceptible, intermediate, or resistant, depending on their level of infection.
For each plant, the RPW8 gene and 12 microsatellite loci were sequenced using commercially available PCR and sequencing technologies. For the neutrality test, microsatellite loci that are in linkage disequilibrium with RPW8 were included. Statistical analysis of the results were then carried out.
It was found that
· Populations were highly diverse and significantly differentiated at neutral microsatellite loci and therefore fulfilled the criteria for inclusion in the study.
· variation in resistance to powdery mildew was found within most of the study populations.
· Different frequencies of disease phenotype between populations was linked to high genetic variation in RPW8.
· RPW8 is not the only genetic factor involved in resistance to powdery mildew.
· There was no evidence that selection was the agent of maintenance of genetic variation at RPW8.
