Identification and functional analysis of the turnip yellow mosaic tymovirus subgenomic promoter

Most plant viruses rely on the production of subgenomic RNAs (sgRNAs) for t he expression of their genes and survival in the plant. Although this is a widely adopted strategy among viruses, the mechanism(s) whereby sgRNA produ ction occurs remains poorly defined. Turnip yellow mosaic tymovirus (TYMV) is a positive-stranded RNA virus that produces an sgRNA for the expression of its coat protein. Here we report that the subgenomic promoter sequence o f TYMV is located on a 494-nucleotide fragment, containing previously ident ified highly conserved sequence elements, which are shown here to be essent ial for promoter function. After duplication, the subgenomic promoter can b e inserted into the coat protein open reading frame, giving rise to the in vivo production of a second sgRNA. It is suggested that this promoter can f unction when contained on a different molecule than viral genomic RNA. This interesting trait may be of general use for plant and plant virus research .