Marina Caillaud and her colleague, Sara Via, received a grant for $362,634, which IC will receive $92,800, from the USDA. The project is entitled, "Genetic Mapping and Molecular Characterization of Feeding Specializatin in Pea Aphid Host Races". It is a 3 year grant beginning this month.
ABSTRACT: We propose to study the molecular basis of feeding specialization in two divergent host races of the pea aphid Acyrthosiphon pisum. First, a genetic linkage map of the pea aphid genome will be made using 200 microsatellite (SSR) markers. These markers will allow us to greatly improve the precision of the existing linkage map for the pea aphid, which was made by the PI with AFLP markers. Moreover, because many of the SSR markers are expected to cross-amplify in closely related aphid species, including many important crop pests, the tools generated by this proposal will be of great use to the national and international community of insect geneticists focusing on aphids. We will use the linkage map to determine which region(s) of the genome contribute to the genetic differences between the races in specialized feeding behavior. For this, we have crossed alfalfa and clover specialists, and have measured the feeding behavior of many F2 offspring. All that remains is to genotype them for the SSR markers. Statistical association between inheritance of a particular chromosomal block (indicated by marker genotype) and the differential acceptance of the two host plants allows us to localize genes that affect feeding specialization to within a 5-10 cM region of the genome. This is a first step toward gene discovery in a non-model system such as the pea aphid, for which many sophisticated molecular tools are not available. Second, we will use a functional genomics approach, suppression subtractive hybridization (SSH), to compare gene expression in gustatory tissues between alfalfa and clover specialists. Our previous work has revealed that taste is a major factor in host recognition by these two races, and the tissue we will use for the expression analysis contains the major taste receptors in the pea aphids. This part of the project will involve the generation of cDNA libraries enriched for differentially-expressed cDNA, which will be carefully screened to determine those that are truly differentially expressed in alfalfa and clover specialists. These cDNAs will be sequenced and compared to genes from model organisms on the small chance of identifying homology with known taste receptors or other genes involved in chemoreception. However, these genes evolve extremely rapidly, tending to limit interspecific homology, so this attempt may not be successful. In a species without a complete genome map, it will be more useful to map the differentially expressed cDNAs onto our linkage map, where we expect that some will co-localize with the QTL that we have found for feeding behavior. These "candidate loci" will be the tools we need for many more detailed molecular analyses of host plant specialization in future granting periods.
https://departments.ithaca.edu/biology/facstaff/mcaillaud/
https://www.ithaca.edu/intercom/article.php/20060301092254850