Transcriptional Profiling of Aphid Resistant and Susceptible Melon (Cucumis Melo) Following Cotton-Melon Aphid (Aphis Gossypii) Feeding. (Paperback)

The interaction between phloem feeding aphids Aphis gossypii (cotton-melon aphid) and Cucumis melo (melon) provides an opportunity to elucidate the means by which a host plant defends itself against aphid attack. The relationship is of scientific as well as economic importance since A. gossypii is among the most destructive insects to agriculture in the U.S. and abroad. The resistance to A. gossypii in melon is controlled at the Vat (V&barbelow;irus a&barbelow;phid t&barbelow;ransmission) locus by a major dominant gene, Vat that has the unique feature of conferring resistance to A. gossypii and resistance to transmission of non-persistent viruses by A. gossypii. The genetic and physical characterization of the Vat gene and its product supports a model of a resistance (R)-gene mediated resistance against A. gossypii that is similar to plant resistance against a wide range of pathogenic organisms. However, the specific recognition, signaling pathways, and proximate causes of resistance against this aphid are unknown. The study hypothesizes that Vat mediated-responses are specific to resistant AR 5(Vat+) plants differing from the basal defense or physiological responses to aphid feeding occurring in susceptible PMR 5 (Vat-) plants and provide physiological and morphological attributes that can counter A. gossypii infestation. The experimental approaches in the study compared the differential expression of genes in susceptible PMR 5 and resistant AR 5 melons following aphid feeding by transcription-based techniques: cDNA-amplified fragment length polymorphisms (AFLP); macroarray analysis; quantitative real time PCR (QRT-PCR), and microarray analyses. The cDNA-AFLP technique generated 1392 differentially expressed amplicons, which in turn were used to construct a microarray. Additional microarray experiments were conducted using melon EST arrays purchased from the Boyce Thompson Institute (BTI) that also allowed comparative expression of genes commonly regulated in response to aphid feeding in melon and tomato plants. The expression of certain candidate genes was further analyzed using reverse northern hybridization and QRT-PCR methods. The detection of an ethylene (ET) receptor in the cDNA-AFLP experiment led to the construction of a short, three-component pathway for the receptor using the pathway building program, Pathway Studio. The short pathway was expanded to include two ET biosynthetic enzymes, seven ET signaling genes, and three downstream ET-responsive genes. The expression of these genes was investigated using QRT-PCR to determine whether the ET defense pathway was transcriptionally activated differently between the nearly isogenic PMR 5 and AR 5 in response to A. gossypii feeding. The study allowed a global view of the differential expression of plant responses as well as provided an in depth observation of a selected defense signaling pathway. The results from the study showed that A. gossypii feeding leads to the differential expression of genes involved in various metabolic, photosynthetic, stress and defense process in susceptible PMR 5 resistant AR 5 melon plants. However the type of genes influenced within each of these processes tend to be different in susceptible PMR 5 and resistant AR 5 plants. Observing changes to the ET signaling pathway following aphid feeding in the two genotypes provided information on the role of ET in the defense response. Some differences in the expression pattern between the PMR 5 and AR 5 are proposed to be due to regulation by the Vat gene, but additional research must be undertaken to further define the roles of specific genes in the interaction.