Lettuce infectious yellows virus: in vitro acquisition analysis using partially purified virions and the whitefly Bemisia tabaci

Virions of lettuce infectious yellows virus (LIYV; genus Crinivirus) were p urified from LIYV-infected plants and their protein composition was analyse d by SDS-PAGE and immunoblotting. Virion preparations contained the major c apsid protein (CP), but the minor capsid protein (CPm), p59 and the HSP70 h omologue were also identified by immunoblot analysis. Immunogold labelling analysis showed that CP constituted the majority of the LIYV virion capsid, but CPm was also part of the capsid and localized to one end of the virion , similar to the polar morphology seen for viruses in the genus Closterovir us. p59 and the HSP70 homologue were not detected on virions by immunogold labelling, but were always detected in virion preparations by immunoblot an alysis. Purified LIYV virions were used for in vitro acquisition analysis w ith Bemisia tabaci whiteflies and were efficiently transmitted to plants. I nfectivity neutralization analyses were done using antisera to the LIYV-enc oded CP, CPm, p59 and HSP70 homologue. Only antiserum to the CPm effectivel y neutralized LIYV transmission by B. tabaci, These data suggest that the L IYV-B. tabaci transmission determinants are associated with purified virion s, and that the LIYV virion structural protein CPm is involved in transmiss ion by B, tabaci.