Beet yellows virus: the importance of being different
Valerian V. Dolja
Department of Botany and Plant Pathology, Oregon State University,
Corvallis, OR 97331, USA
||Type member of the genus Closterovirus,
family Closteroviridae. A member of the alphavirus-like supergroup
of positive-strand RNA viruses.
||Virions are flexuous filaments of
~1300 nm in length and ~12 nm in diameter that are made up of a ~15.5 kb
RNA and five proteins. The major capsid protein forms virion body of
helical symmetry that constitutes ~95% of the virion length. The short
virion tail is assembled by the minor capsid protein, Hsp70-homologue,
~64-kDa protein, and ~20-kDa protein.
||The 5'-most ORFs 1a and 1b encode
leader proteinase and RNA replicase. The remaining ORFs 2-8 are expressed
by subgenomic mRNAs that encode 6-kDa membrane protein, Hsp70 homologue,
~64-kDa protein, minor and major capsid proteins, ~20-kDa protein, and
~21-kDa protein, respectively.
||The principal crop plants affected
by Beet yellows virus (BYV) are sugar beet (Beta vulgaris)
and spinach (Spinacea oleracea). In addition, BYV was reported to
infect ~120 species in 15 families. Most suitable propagation species are Nicotiana
benthamiana, Tetragonia expansa, and Claytonia perfoliata.
Morphology of the BYV virions. (A) Electron micrograph of two BYV
virions. Virion tails marked by arrows were immunogold labelled using
anti-CPm serum (courtesy of Alberto J. Napuli). (B) Atomic force
microscopy image of a single BYV virion. The white appearance of the body
and the grey appearance of the tail are due to a larger depth of the body
compared to that of the tail. (C and D) 3D reconstruction of the virion
ends obtained using atomic force microscopy. Images B-D are courtesy of
Igor Andreev and Michael E. Taliansky.
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