ABSTRACT
In contrast to fungi, which frequently harbor noninfectious dsRNAs genetic elements of viral origin, the great majority of viruses that infect plants have a single-stranded RNA genome of positive polarity. During the replicative cycle, a double-stranded form of the genomic RNA is formed transiently; it is then used as a template by the
virus-encoded RNA-dependent RNA polymerase (RDRP) to generate many copies of positive strand RNA, which are translated, amplified, and encapsidated to form virions. Thus, such infections are characterized by a vast excess of plus strand RNA over dsRNA: the double-stranded form is only transient, and transcription is highly asymmetrical.
