35S promoter-driven cDNAs of barley mild mosaic virus RNA1 and RNA2 are infectious on barley plants.

Full-length cDNAs of barley mild mosaic bymovirus RNA1 and RNA2 were cloned downstream of a modified cauliflower mosaic virus 35S promoter with double enhancer. Mechanical inoculation of barley seedlings with a mixture of both cDNAs resulted in systemic mosaic symptoms, typical of barley mild mosaic virus infection. The presence of both RNA species and their gene products in the systemically infected leaves was demonstrated by RT-PCR and Western blot analyses, respectively. Virions were detected by immunogold labelling, demonstrating that the RNAs are encapsidated. This is the first report of the 35S promoter used in successfully infecting a monocot plant host with cDNA from a strictly monocot plant RNA virus.