Coat protein of cucumber necrosis virus is not required for efficient generation or accumulation of defective interfering RNAs

Abstract

It is generally assumed that defective interfering (DI) forms of viruses are encapsidated in structural proteins encoded by the helper virus. Virion RNA extracts from cucumber necrosis virus (CNV) infections showing high levels of cellular DI RNAs contain barely detectable levels of DI RNAs, suggesting that DI RNAs are encapsidated very inefficiently. In addition, accumulation of CNV DI RNAs occurs at equal efficiency in coinoculated plants using either synthetic wild-type CNV genomic RNA as helper or a mutant of CNV which lacks the coat protein-coding sequence. Together this shows that the CNV coat protein is not required for efficient accumulation of CNV DI RNA in plants. Factors that could account for the high level of CNV DI RNAs in plants are discussed.