Effects of structural modifications upon the accumulation in planta of replicons derived from beet necrotic yellow vein virus RNA 3

Beet necrotic yellow vein virus (BNYVV) RNA 3 from which all but the 3' and 5' 'core' replication origins (promotors) have been deleted replicates whe n coinoculated to Chenopodium quinoa with viral RNAs 1 and 2. The resulting 'replicon' can be used to express inserted heterologous sequences in plant a. The effects of alterations of replicon structure on its efficiency of ac cumulation in planta were examined. Inclusion of up to similar to 240 nucle otides of sequence from the region immediately upstream of the core 3'-prom oter sequence increased replicon accumulation, suggesting that this region contains specific replication enhancer elements. Insertion of non-viral 'sp acer' sequences between the core promoters also increased replicon accumula tion, provided that no strong secondary structure was present. The highly h omologous 3'-terminal core promoters of BNYVV RNAs 1, 2 and 4 could substit ute for the RNA 3 core promoter but were generally somewhat less effective. Go-inoculation of full-length RNA 3 but not RNA 4 interfered with accumula tion of the RNA 3-based replicons.