Mutation of a chloroplast-targeting signal in Alternanthera mosaic virus TGB3 impairs cell-to-cell movement and eliminates long-distance virus movement.
Cell-to-cell movement of potexviruses requires coordinated action of the coat protein and triple gene block (TGB) proteins. The structural properties of Alternanthera mosaic virus (AltMV) TGB3 were examined by methods differentiating between signal peptides and transmembrane domains, and its subcellular localization was studied by Agrobacterium-mediated transient expression and confocal microscopy. Unlike potato virus X (PVX) TGB3, AltMV TGB3 was not associated with the endoplasmic reticulum, and accumulated preferentially in mesophyll cells. Deletion and site-specific mutagenesis revealed an internal signal VL(17,18) of TGB3 essential for chloroplast localization, and either deletion of the TGB3 start codon or alteration of the chloroplast-localization signal limited cell-to-cell movement to the epidermis, yielding a virus that was unable to move into the mesophyll layer. Overexpression of AltMV TGB3 from either AltMV or PVX infectious clones resulted in veinal necrosis and vesiculation at the chloroplast membrane, a cytopathology not observed in wild-type infections. The distinctive mesophyll and chloroplast localization of AltMV TGB3 highlights the critical role played by mesophyll targeting in virus long-distance movement within plants.
Lim
Hyoun-Sub
HS
USDA-ARS, Plant Sciences Institute, Molecular Plant Pathology Laboratory, B-004, 10300 Baltimore Avenue, Beltsville, MD 20705, USA.
Vaira
Anna Maria
AM
CNR, Istituto di Virologia Vegetale, Strada delle Cacce 73, Torino 10135, Italy.|USDA-ARS, Plant Sciences Institute, Molecular Plant Pathology Laboratory, B-004, 10300 Baltimore Avenue, Beltsville, MD 20705, USA.
Bae
Hanhong
H
School of Biotechnology, Yeungnam University, Geongsan 712-749, Republic of Korea.
Bragg
Jennifer N
JN
USDA-ARS, Western Regional Research Center, 800 Buchanan Street, Albany, CA 94710, USA.
Ruzin
Steven E
SE
University of California-Berkeley, CNR, 381 Koshland Hall, Berkeley, CA 94720, USA.
Bauchan
Gary R
GR
USDA-ARS, Plant Sciences Institute, Electron and Confocal Microscopy Unit, B-465, 10300 Baltimore Avenue, Beltsville, MD 20705, USA.
Dienelt
Margaret M
MM
USDA-ARS, Plant Sciences Institute, Molecular Plant Pathology Laboratory, B-004, 10300 Baltimore Avenue, Beltsville, MD 20705, USA.
Owens
Robert A
RA
USDA-ARS, Plant Sciences Institute, Molecular Plant Pathology Laboratory, B-004, 10300 Baltimore Avenue, Beltsville, MD 20705, USA.
Hammond
John
J
USDA-ARS, Plant Sciences Institute, Molecular Plant Pathology Laboratory, B-004, 10300 Baltimore Avenue, Beltsville, MD 20705, USA.
D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000378:metabolism*; D005822:Genetic Vectors; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010935:Plant Diseases / Q000821:virology*; D017863:Potexvirus / Q000235:genetics / Q000472:pathogenicity*; D021382:Protein Sorting Signals; D021381:Protein Transport; D012231:Rhizobium / Q000235:genetics; D016415:Sequence Alignment; D017384:Sequence Deletion; D014026:Nicotiana / Q000821:virology; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
D021382:Protein Sorting Signals; D014764:Viral Proteins