Apple chlorotic leaf spot virus 50 kDa protein is targeted to plasmodesmata and accumulates in sieve elements in transgenic plant leaves

We investigated the in situ localization of the 50 kDa protein encoded by O RF2 of Apple chlorotic leaf spot virus (ACLSV) genome which is thought to b e a movement protein. In immunogold electron microscopy of ACLSV-infected C henopodium quinoa leaves, the 50 kDa protein was localized on plasmodesmata and nearby cytoplasm. Observation of transgenic Nicotiana occidentalis lea ves expressing the 50 kDa protein fused to enhanced green fluorescent prote in (EGFP) by fluorescence and confocal laser scanning microscopes revealed that green fluorescence was observed as spots on the cell wall or strands p assing through the cell wall of several cell types, i.e., epidermal, palisa de and spongy mesophyll and collenchyma cells. In transverse and longitudin al sections of leaf veins of transgenic plants showed that the 50K-EGFP fus ion accumulated in sieve elements and formed an extensive interconnecting n etwork of threadlike structure. These results indicated that ACLSV 50 kDa p rotein can target plasmodesmata and traffic into sieve elements.