Mediation of plant-herbivore interactions by foliar bacterial endophytes: A test using a native Pseudomonas-mustard-insect interaction system

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Parasites are among the strongest negative factors in the health and performance of both plants and animals. Plant and animal hosts have in turn evolved robust immune systems that are organized into distinct branches that respond to different types of parasites. However, evidence suggests that when attack by one type of parasite activates one branch of the immune system, other branches can be de-activated. This could mean that co-infection by more than one type of parasite could partly defeat an immune response and have more serious combined effects than expected from just adding the effects of separate attacks by each parasite. The project will test this using a native plant species and its natural, pathogenic bacteria and herbivores in an alpine ecosystem in the Rocky Mountains. The researchers will conduct field and laboratory experiments to show if prior infection with leaf-dwelling bacteria renders the plants more susceptible to attack by leaf-chewing herbivores, and vice versa. Use of molecular techniques will further show if this is accompanied by de-activation of the branches of the immune system of the plant that are respectively responsible for resistance to bacteria and herbivores. This project will help fill an important gap in our understanding of the importance of co-infection in nature.This project will train undergraduate and graduate students, postdoctoral scientists, and a high school teacher in ecology, molecular biology, and microbiology. The award will also further the career of a young investigator by providing his first major federal funding. The study species are relatives of major agricultural pathogens, pests, and crop plants, so results should help understand how to reduce agricultural losses. The research should also have applications to medicine, because co-infection is also a health problem in humans. For example, prior infection of people with intestinal worms can lead to increased susceptibility to microbial infections.