VASCULAR MOVEMENT OF BEET NECROTIC YELLOW VEIN VIRUS IN BETA-MARCROCARPA IS PROBABLY DEPENDENT ON AN RNA 3 SEQUENCE DOMAIN RATHER THAN A GENE-PRODUCT

RNAs 1 and 2 of beet necrotic yellow vein virus (BNYVV) carry the func tions enabling viral RNA replication, cell-to-cell movement, virus ass embly and vascular movement of the virus in the systemic host Spinacea oleracea, In Beta macrocarpa, on the other hand, BNYVV RNA 3 is requi red for vascular movement. Replication-competent RNA 3 transcripts car rying various point mutations and deletions were coinoculated with RNA s 1 and 2 to young leaves of B.macrocarpa and the ability of the virus to multiply on the inoculated leaves and to invade the plant systemic ally was examined, None of the RNA 3 mutants tested interfered with vi rus multiplication in the inoculated leaves. Point mutations designed to specifically block or truncate translation of the ORFs of the two k nown RNA 3 gene products, P25 and N, did not interfere with vascular m ovement, Vascular movement was not inhibited by deletions eliminating the short 5'-proximal ORF on RNA 3 (ORF A) or by point mutations block ing putative translation of the short 5'-proximal ORF (ORF S) on RNA 3 sub, a subgenomic RNA derived from RNA 3, On the other hand, deletions in a 'core region' encompassing nucleotides 1033-1257 of RNA 3 comple tely blocked vascular movement of the virus while removal of sequences flanking the core region lowered its efficiency, The observations sug gest that some feature of the RNA 3 sequence rather than an RNA-3 code d protein is important for vascular movement of BNYVV in B.macrocarpa.