2007 Annual Report 1a.Objectives (from AD-416) Plant-insect interaction is complex and dynamic; however, little is known about the molecular basis of plant defense against insect pests. The research objectives of this project are to explore the diversity of host responses to aphid attack and to gain a better understanding of the mechanisms underlying the interactions between host plants and phloem-feeding insects. In this project, host plants and attacking aphids will be studied simultaneously using genetic and functional genomics tools, which will lead to the identification of virulence factors of the pest aphids and novel resistance genes of host plants, and reveal important mechanisms that mediate direct and indirect defenses. It is anticipated that information obtained from these studies, based on the combined knowledge of the defense systems operating in the plants and the attacking systems used by pests, will contribute to the development of crop plants with durable and multi-mechanistic resistance to insect pests. 1b.Approach (from AD-416) In this project, sorghum plant and phloem-feeding aphids will be used as the model system to study plant-insect interaction, which may extend to functional genomic studies in other crop species. Insect attack elicits a large transcriptional reorganization leading to activation of host defense. Elicitors in the aphid oral secretions can account for aphid-specific responses. Thus, genome-wide gene expression profiling will be conducted to identify candidate genes potentially responsible for induced plant defense against aphid pests. Subsequently, genetic and molecular tools are used to define the function of those newly identified genes and the gene products in host defense. 3.Progress Report This report documents research conducted under a specific cooperative agreement between ARS and Oklahoma State University. Additional details of research can be found in the report for the parent CRIS 6217-21000-006-00D, Genetic Improvement of Insect Pest Resistance in Wheat, Barley, and Sorghum. The phloem-feeding by greenbug (Schizaphis graminum) elicits unique interactions with their host plants. To investigate expression profiles of sorghum genes responsive to greenbug feeding, two subtractive cDNA libraries were constructed through different combinatorial subtractions in strong greenbug resistance sorghum M627 line and susceptible Tx7000 line with or without greenbug infestation. A total of 3,508 cDNAs were selected from the two cDNA libraries, and subsequent cDNA microarray and northern blot analyses were performed for identification of sorghum genes responsive to greenbugs. In total, 157 sorghum transcripts were identified to be differentially expressed by greenbug feeding. The greenbug responsive genes isolated were classified to nine categories according to functional roles in plant metabolic pathways, such as defense, signal transduction, cell wall fortification, oxidative burst/stress, photosynthesis, development, cell maintenance, abiotic stress, and unknown function. Overall, the profiles of sorghum genes responsive to greenbug phloem-feeding shared common identities with other expression profiles known to be elicited by diverse stresses, including pathogenesis, abiotic stress, and wounding. The ADODR has been actively participated in this cooperative research working both independently and in conjunction with the cooperator. The ADODR monitored activities through regular meetings, email and telephone communications.