MOLECULAR ANALYSIS OF THE POTHOS LATENT VIRUS GENOME

Pothos latent virus (PoLV) is an isometric virus with a positive-sense , single-stranded RNA genome of 4415 nt. The genome contains five open reading frames (ORF), coding for five proteins with approximate molec ular masses of 25, 84, 40, 27 and 14 kDa, respectively, In vitro synth esized PoLV RNA was infectious to Nicotiana benthamiana plants and pro toplasts, but could not support replication of the defective interferi ng (DI) and satellite RNAs associated with Cymbidium ringspot tombusvi rus, No DI RNA related to PoLV was generated after repeated passaging with infected sap. Mutagenesis studies defined the role of the ORF 4 p roduct (27 kDa) as a movement protein, and the ORF 5 product (14 kDa) as being responsible for symptom severity. Moreover, it was shown that the coat protein (CP) is important in regulating synthesis of the 14 kDa protein, excess production of which is lethal to infected plants. CP mutants defective in capsid formation infected plants systemically and induced severe necrotic symptoms. Conversely, CP mutants able to f orm apparently normal virus particles induced symptoms indistinguishab le from those elicited by wild-type virus.