The phloem-specific feeding style of aphids poses unique challenges, both to the host plants, which must mount defense responses against herbivores that do little overt damage, and to the aphids, which must adapt to a nutritionally imbalanced and potentially toxic food source. Myzus persicae (green peach aphids) are important agricultural pests and also feed readily from Arabidopsis. We are studying plant recognition of M. persicae salivary components, Arabidopsis gene expression changes induced during aphid feeding, and plant secondary metabolites that contribute to aphid defense. On the aphid side of the interaction, our goals are to identify M. persicae enzymes that detoxify plant metabolites, as well as aphid gene expression changes that are induced in response to plant defenses.
Plant amino acid metabolism
Unlike plants, which can synthesize the complete repertoire of protein amino acids, humans and other animals must obtain certain essential amino acids in their diets. However, despite the nutritional importance of plant-derived amino acids, many aspects of plant amino acid metabolism remain uninvestigated. Recent research in the lab has been focused on studying the function two plant enzymes, threonine aldolase and homocysteine methyltransferase, which were discovered in a mutant screen for Arabidopsis lines with altered seed amino acid content. Whereas threonine aldolase mutations increase seed threonine levels, homocysteine methyltransferase mutations increase seed methionine accumulation. Manipulation of these two enzymes could be used to improve the nutritional value of crop plants in which threonine and/or methionine are limiting for mammalian diets.
We are investigating plant-insect interactions using the small crucifer plant Arabidopsis thaliana (Arabidopsis) and Myzus persicae (peach-potato aphid) as a model system. Unlike chewing insects (e.g. caterpillars), which eat whole leaves or other parts of the plant, aphids use their stylet mouth-parts to ingest phloem sap. Thus, plant defenses against these two kinds of herbivory are likely to be very different. A major project in the lab is to study natural variation in Arabidopsis-aphid interactions. Arabidopsis ecotypes vary in their sensitivity to aphids, and aphid lineages also vary in their ability to grow on particular ecotypes. Crosses between resistant and sensitive lines of Arabidopsis are being used to genetically map genes that confer aphid resistance or sensitivity. In other work, we are investigating the effect of known Arabidopsis mutations on aphid fecundity, and are using high performance liquid chromatography (HPLC) analysis of plant tissue to identify small molecules that might play a role this insect-plant interaction.
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