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

Summary

Beet necrotic yellow vein virus (BNYVV) RNA 3 from which all but the 3′ and 5′‘core’ replication origins (promotors) have been deleted replicates when coinoculated to Chenopodium quinoa with viral RNAs 1 and 2. The resulting ‘replicon’ can be used to express inserted heterologous sequences in planta. The effects of alterations of replicon structure on its efficiency of accumulation in planta were examined. Inclusion of up to ∼240 nucleotides of sequence from the region immediately upstream of the core 3′-promoter sequence increased replicon accumulation, suggesting that this region contains specific replication enhancer elements. Insertion of non-viral ‘spacer’ sequences between the core promoters also increased replicon accumulation, provided that no strong secondary structure was present. The highly homologous 3′-terminal core promoters of BNYVV RNAs 1, 2 and 4 could substitute for the RNA 3 core promoter but were generally somewhat less effective. Co-inoculation of full-length RNA 3 but not RNA 4 interfered with accumulation of the RNA 3-based replicons.