Specific inclusion bodies are associated with replication of lettuce infectious yellows virus RNAs in Nicotiana benthamiana protoplasts.

Nicotiana benthamiana mesophyll protoplasts, either mock-inoculated or inoculated using in vitro transcripts derived from lettuce infectious yellows virus (LIYV) RNA 1- and/or RNA 2-cloned cDNAs were analysed by transmission electron microscopy (TEM) and, in some cases, also by immunogold labelling. TEM revealed the main cytopathological effects of LIYV infections in N. benthamiana protoplasts infected with RNAs 1 and 2: (a) typical closterovirus-induced (beet yellows virus-type) accumulations of vesiculated cytoplasmic membranes as inclusion bodies, sometimes with associated virions; (b) scattered aggregations of virions within the cytoplasm; and (c) electron-dense plasmalemma deposits. These were not seen in mock-inoculated protoplasts. Protoplasts inoculated only with LIYV RNA 1 contained vesiculated cytoplasmic inclusion bodies, but not virions or plasmalemma deposits. Thus, infection by only LIYV RNA 1 is sufficient to induce characteristic closterovirus vesiculated cytoplasmic inclusion bodies. However, both LIYV RNAs 1 and 2 are needed for production of virions and plasmalemma deposits.