FUNCTIONAL GENOMICS AND ANALYSIS OF GREENBUG SECRETED SALIVARY PROTEIN GENES: DEVELOPMENT OF TOOLS FOR THE APHIDS AND OTHER PHLOEM-FEEDING INSECTS
Xiaoyan Tang, Plant Pathology
Gerald Reeck, Biochemistry
John Reese, Entomology
Frank White, Plant Pathology

PROJECT SUMMARY
Phloem-feeding insects such as aphids and whiteflies release saliva proteins into plant cells and tissues. Saliva proteins are believed to assist insect feeding, but their identity and functions in phloem-feeding are largely unknown. Saliva proteins are also likely to be involved in host recognition by triggering the plant disease resistance responses. This proposal is to develop tools for identification of saliva proteins that function in plant cells either for insect feeding or host recognition and defense. The goals are made possible by several recent developments. First, advancements in DNA sequencing technique enables the identification of genes expressed in salivary gland at a genome scale; and, second, the understanding of bacterial type III secretion system (TTSS) in delivery of effector proteins of bacterial pathogens into the host cells allows the use of the TTSS as a research tool for pathogen and pest virulence effectors. The TTSS delivers effectors into host cells by recognizing the secretion signal peptide at the N-terminus of proteins. The system will provide a tool for delivery of the salivary proteins into plant cells and facilitate their functional analysis. We have designed a genomics-enabled strategy to identify greenbug proteins that are injected into the plant cells and propose the following two objectives:
1. We will identify candidate effector genes from greenbug by high through-put sequencing of salivary gland full length cDNAs, bioinformatic analysis, and assays for specific gene expression in salivary gland.
2. We will develop a method for delivering candidate effector proteins into plant cells using the bacterial TTSS and conduct phenotyping of effector genes on the plants host and non-host to greenbug.

The identification of aphid genes involved in plant interaction is critical for the understanding of aphid feeding and development of rational insect control strategies. The delivery system to be developed will be applicable to a variety of other insects of significant economic value.