Plant-insect interactions: The tomato defense response following feeding by phloem-feeding whiteflies

The study of plant defense has been a very intense area of research for many years. The study of plant defenses in response to phloem-feeding insects has lagged far behind the study of other plant-pathogen interactions. The phloem-feeding whiteflies have wreaked havoc on crop production throughout the southern US and worldwide. Whiteflies not only vector deadly plant viruses, but also remove photo-assimilates from plants. Specifically the silverleaf whitefly causes several developmental disorders in plants including tomatoes, broccoli and squash. The characterization of plant defense following whitefly feeding will not only determine what changes in gene expression are taking place after whitefly feeding but may help in devising new strategies for protecting crops against whitefly feeding.; I characterized the defense gene expression changes following feeding by two species of whiteflies (Bemisia argentifolii and Trialeurodes vaporariorum). This was accomplished using two methods. Chapter One describes RNA blot analyses that monitored changes in defense- and wound-response genes in tomato leaves that had been infested with whiteflies. These data showed that the feeding of whiteflies induced a plant defense response that is similar to fungal or bacterial infections. However, whitefly feeding does not seem to induce a wound response in tomato leaves. This was supported by the analysis of LapA:GUS transgenic tomato plants after whitefly infestation.; The second chapter characterized the defense-related gene expression changes following whitefly feeding using differential RNA display. This method required small quantities of RNA and utilized PCR to amplify cDNAs. Novel cDNAs were found to be induced following whitefly feeding and one was chosen to be fully characterized. After sequencing the full-length cDNA and genomic clones, the Wfi1 gene was found to be an analog of the mammalian gp91-phox gene. This protein is involved in the generation of active oxygen species used to kill invading pathogens. The Wfi1 RNA accumulated following whitefly feeding, bacterial infection, methyl jasmonate and ethylene treatment of tomato plants.; This research provides the basis for more thorough investigations in whitefly-plant interactions. With the discovery that plants also induce an NADPH oxidase when attacked by pathogens, a better understanding of plant defense will lead to the improvement of agriculture throughout the world.