Replication of barley stripe mosaic virus (BSMV) is thought to be associated with proplastids and chloroplasts. CLSM studies at SCRI have shown that the BSMV triple-gene block 2 (TGB2) and and yb proteins localise to chloroplasts in the presence of viral RNA. TEM analysis showed that BSMV infection resulted in the formation of cytoplasmic inclusions, containing virus-like particles, within chloroplasts. Similarly, CLSM studies of potato mop-top virus (PMTV) have shown that its TGB2 protein, even in the absence of viral RNA, can localise to the outer membrane of plastids. TEM observations show that, as with BSMV, infection by PMTV result in chloroplast deformation and the formation of cytoplasmic inclusions.