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J. Virol., Dec 1997, 9157-9162, Vol 71, No. 12
IM Moreno, JM Malpica, E Rodriguez-Cerezo and F Garcia-Arenal
The nucleotide substitution C-->A at nucleotide 100 of tomato aspermy
cucumovirus (TAV) strain V (V-TAV) RNA segment 3 (RNA3) introduces an ocher
stop at the fourth codon of the movement protein open reading frame.
Experiments with RNA transcripts from full-length clones showed that this
mutation abolished cell-to-cell movement and, thus, infectivity in planta.
Heterogeneity analyses on stock V-TAV virion RNA showed that an A at
position 100 was present in the molecular population of RNA3 at a frequency
of 0.76 and that a C at this position was present at a frequency of 0.24.
This result indicates that a fraction of RNA3 molecules complements
cell-to-cell movement of movement-defective molecules. It was shown that
the mutation C-->A conferred enhanced RNA replication of the defective
mutant in tobacco protoplasts. The effect of the mutation on replication
was dependent on sequence context, since the same mutation did not affect
the replication efficiency in the related TAV strain 1 RNA3. Competition
experiments in tobacco protoplasts were done to estimate the fitness during
a cell invasion cycle of the movement-defective mutant relative to the wild
type (wt). From these data, a lower limit to the degree of complementation
of movement-defective molecules by movement-competent ones could be
estimated as 0.13. This estimate shows that complementation may play an
important role in the determination of genetic structure in RNA genome
populations. A further effect of the enhanced replication of the
movement-defective mutant was the efficient competition with the wt for the
initiation of infection foci in planta.
Copyright © 1997, American Society for Microbiology
A mutation in tomato aspermy cucumovirus that abolishes cell-to-cell movement is maintained to high levels in the viral RNA population by complementation
Departamento de Biotecnologia, E.T.S.I. Agronomos, Universidad Politecnica de Madrid, Spain.
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