APHID TRANSMISSION AND SYSTEMIC PLANT INFECTION DETERMINANTS OF BARLEY YELLOW DWARF LUTEOVIRUS-PAV ARE CONTAINED IN THE COAT PROTEIN READTHROUGH DOMAIN AND 17-KDA PROTEIN, RESPECTIVELY

Proteins encoded by open reading frames (ORF) 3, 4, and 5 of the barle y yellow dwarf luteovirus genome are translated from a single subgenom ic RNA. The structural proteins are encoded by ORF 3 (coat protein) an d ORF 5 (readthrough domain) and contain undefined domains that regula te the movement of virus through aphid vectors. The biological functio n of the nonstructural 17-kDa protein encoded by ORF 4 is unknown. A c omplementation method was employed to test the ability of barley yello w dwarf virions carrying mutations within the readthrough domain and t he 17-kDa protein to be transmitted by aphids and to cause systemic in fections in plants. We show that the readthrough domain is required fo r aphid transmission; however, it is not required for virus to be take n up by aphid hindgut cells and released into the hemocoel. The circul ative pathway of luteoviruses in aphid vectors requires that virus be actively transported from the hemolymph into the salivary system. Thus , it appears that the readthrough domain is required for transport of virus through membranes of the aphid salivary glands. Furthermore, the readthrough domain was not required for systemic infection of plants, but did influence the accumulation of virus in infected plants. The 1 7-kDa protein is required for the systemic infection of plants. (C) 19 96 Academic Press, Inc.