Visual monitoring of Cucumber mosaic virus infection in Nicotiana benthamiana following transmission by the aphid vector Myzus persicae

The single-stranded, positive-sense and tripartite RNA virus Cucumber mosaic virus (CMV) was used in this study as a method for monitoring the initial stages of virus infection following aphid transmission. The RNA2 of CMV was modified to incorporate, in a variety of arrangements, an open reading frame (ORF) encoding an enhanced green fluorescent protein (eGFP). The phenotypes of five engineered RNA2s were tested in Nicotiana tabacum, Nicotiana clevelandii and Nicotiana benthamiana. Only one construct (F4), in which the 2b ORF was truncated at the 3' end and fused in-frame with the eGFP ORF, was able to systemically infect N. benthamiana plants, express eGFP and be transmitted by the aphid Myzus persicae. The utility of this construct was demonstrated following infection as early as one day post-transmission (dpt) continuing through to systemic infection. Comparisons of the inoculation sites in different petiole sections one to three dpt clearly showed that the onset of infection and eGFP expression always occurred in the epidermal or collenchymatous tissue just below the epidermis; an observation consistent with the rapid time frame characteristic of the non-persistent mode of aphid transmission.