E. Waigmann et P. Zambryski, TOBACCO MOSAIC-VIRUS MOVEMENT PROTEIN-MEDIATED PROTEIN-TRANSPORT BETWEEN TRICHOME CELLS, The Plant cell, 7(12), 1995, pp. 2069-2079
Tobacco mosaic virus movement protein (TMV MP) is required to mediate
viral spread between plant cells via plasmodesmata. Plasmodesmata are
cytoplasmic bridges that connect individual plant cells and ordinarily
limit molecular diffusion to small molecules and metabolites with a m
olecular mass up to 1 kD. Here, we characterize functional properties
of Nicotiana clevelandii trichome plasmodesmata and analyze their inte
raction with TMV MP. Trichomes constitute a linear cellular system and
provide a predictable pathway of movement. Their plasmodesmata are fu
nctionally distinct from plasmodesmata in other plant cell types; they
allow cell-to-cell diffusion of dextrans with a molecular mass up to
7 kD, and TMV MP does not increase this size exclusion limit for dextr
ans. In contrast, the 30-kD TMV MP itself moves between trichome cells
and specifically mediates the translocation of a 90-kD beta-glucuroni
dase (GUS) reporter protein as a GUS::TMV MP fusion. Neither GUS by it
self nor GUS in the presence of TMV MP moves between cells. These data
imply that a plasmodesmal transport signal resides within TMV MP and
is essential for movement. This signal confers selectivity to the tran
slocated protein and cannot function in trans to support movement of o
ther molecules.