To monitor infection of Nicotiana benthamiana by tobacco mosaic virus (TMV)
, leaves were inoculated with viral constructs expressing the green fluores
cent protein (GFP) from jellyfish (Aequorea victoria) fused to the movement
protein (MP) of TMV (MP:GFP) or as a free GFP in place of the coat protein
(CP), Infection sites produced by TMV expressing the MP:GFP appeared as fl
uorescent rings larger in diameter and less fluorescent than fluorescent di
sks induced by constructs encoding free GFP, These results suggest that pro
tein expression driven by the MP subgenomic promoter (sgp) initiates and en
ds earlier and is at lower level than that observed for proteins driven by
the CP sgp, Similarly, analyses of cross sections through the infection sit
es revealed that in different cell types the accumulation of MP:GFP was reg
ulated differently than the accumulation of free GFP, Immunocytochemistry a
nd electron microscopy showed that near the leading edge of the fluorescent
ring the MP:GFP and the viral 126 kDa and 183 kDa replicase proteins accum
ulated in paired cytoplasmic bodies that formed often on opposite sides of
adjacent cell walls containing plasmodesmata, In the dimly fluorescent cent
er of the rings the 126 kDa and 183 kDa proteins, but not the MP:GFP, were
localized in unpaired cytoplasmic bodies containing ropelike, fibrillar str
uctures, The paired bodies were similar to previously described viroplasms,
while the unpaired bodies were similar to X-bodies, These data indicate th
at the accumulation of proteins expressed from different sgps of TMV has a
specific spatial and temporal pattern in planta, In addition, the cytoplasm
ic bodies containing the 126 kDa and 183 kDa proteins are dynamic entities
whose protein content and subcellular location change during infection.