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 b y transmission electron microscopy (TEM) and, in some cases, also by i mmunogold labelling, TEM revealed the main cytopathological effects of LIYV infections in N. benthamiana protoplasts infected with RNAs 1 an d 2: (a) typical closterovirus-induced (beet yellows virus-type) accum ulations of vesiculated cytoplasmic membranes as inclusion bodies, som etimes with associated virions; (b) scattered aggregations of virions within the cytoplasm; and (c) electron-dense plasmalemma deposits. The se were not seen in mock-inoculated protoplasts. Protoplasts inoculate d only with LIYV RNA 1 contained vesiculated cytoplasmic inclusion bod ies, but not virions or plasmalemma deposits. Thus, infection by only LIYV RNA 1 is sufficient to induce characteristic clostero-virus vesic ulated cytoplasmic inclusion bodies. However, both LIYV RNAs 1 and 2 a re needed for production of virions and plasmalemma deposits.