Vector Specificity in Potyvirus Transmission: Role of the Helper Component

Objectives: The overall objective of this research was to gain a better understanding of how potyviruses interact with their aphid vectors. The aim was to design new approaches for prevention of potyvirus spread by aphids. The sub-objectives included: (1). Determination of which of the HCs of different potyviruses effect efficient transmission by specific aphid vectors; (2). Determine regions in the HC that play a role in their compatibility with the vector; (3). Determine the factors within the aphid stylets that modify HC activity in transmission. Background of the topic: Background to the topic: Potyviruses are typical non persistent viruses. They are retained within the vector’s stylets and rapidly lost by the vector. Some potyviruses greatly differ in their ability to be transmitted by different aphid species. The present work centered on analyzing factors that may modify the interactions between the "helper component"(HC), the virions and the aphid species involved. Major conclusions, solutions and achievements: It was established that specificity of transmission may depend on aphid species used. It was also shown that specificity may depend on the affinity between HC and virion. However, the attempts to create activechimericTEV/TuMVHCs or ZYMV/TuMVHCs to identify the regions that determine interaction with a specific vector(s), were not successful. More progress was attained in objective 3: In Kentucky, tests were conducted to ascertain retention tobacco vein mottling virus  (TVMV) HC in the stylets of L. erysimicompared to that in M. persicae. Ultra-thin section of stylets of aphids that fed on either TuMVHC or TVMVHC antibodies were treated with gold-labeled goat anti-rabbit antibodies.TuMV was seen in 25% the stylets of L. erysimi when they acquired TuMVHC but not when they acquired TVMVHC. In M. persicae, TVMVHC was present in 30% of the stylets. . Transmission with TuMVHC was not affected by treatment with L. erysimi saliva whereas transmission with PVYHC (which also is not functional in L. erysimi) was consistently reduced by about half. Saliva from M. persicaehad essentially no effect on either HC. The possible role aphid cuticle proteins (which are found on the stylets surface) in the association with the potyviralHC was investigated in Israel. This was done adopting two approaches: (a) isolation of cuticular proteins from aphid cuticle; (b) screening for genes encoding cuticular proteins. In the first approach, we succeeded in extracting proteins from whole homogenized M. persicaeusing concentrated urea. The extracted protein served for preparation of anti cuticular antibodies. In overlay experiments it was found that cuticular proteins specifically bind to ZYMVHC. In addition, a cDNA library of M. persicae has been prepared. Genes encoding for cuticular proteins were ascertained using antibodies to cuticular proteins. This allowed reporting the sequence of the first cuticular gene of aphids and comparing it in six aphid species. Implications, scientific and agricultural: Achievements: (1) Proofs were provided for the role of the specificity of the aphid species to the HC of certain potyviruses; (2) aphid’s saliva was found to affects transmission efficiency; (3) cuticle protein genes were isolated for the first time from aphid species and an association of cuticle protein with the potyviralHC was discerned. Agricultural and/or economic impact of the research findings: At this stage of research, our finding do not bear an agricultural or economic impact.