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Journal of Virology, December 1998, p. 10050-10057, Vol. 72, No. 12
Istituto di Fitovirologia Applicata, CNR,
10135 Torino, Italy,1 and
Institut des
Sciences Végétales, CNRS, 91198 Gif-sur-Yvette,
France2
Received 17 April 1998/Accepted 25 August 1998
A functional capsid protein (CP) is essential for host plant
infection and insect transmission in monopartite geminiviruses. We
studied two defective genomic DNAs of tomato yellow leaf curl virus
(TYLCV), Sic and SicRcv. Sic, cloned from a field-infected tomato, was
not infectious, whereas SicRcv, which spontaneously originated from
Sic, was infectious but not whitefly transmissible. A single amino acid
change in the CP was found to be responsible for restoring infectivity.
When the amino acid sequences of the CPs of Sic and SicRcv were
compared with that of a closely related wild-type virus (TYLCV-Sar),
differences were found in the following positions: 129 (P in Sic and
SicRcv, Q in Sar), 134 (Q in Sic and Sar, H in SicRcv) and 152 (E in
Sic and SicRcv, D in Sar). We constructed TYLCV-Sar variants containing
the eight possible amino acid combinations in those three positions and
tested them for infectivity and transmissibility. QQD, QQE, QHD, and
QHE had a wild-type phenotype, whereas PHD and PHE were infectious but nontransmissible. PQD and PQE mutants were not infectious; however, they replicated and accumulated CP, but not virions, in Nicotiana benthamiana leaf discs. The Q129P replacement is a
nonconservative change, which may drastically alter the secondary
structure of the CP and affect its ability to form the capsid. The
additional Q134H change, however, appeared to compensate for the
structural modification. Sequence comparisons among
whitefly-transmitted geminiviruses in terms of the CP region studied
showed that combinations other than QQD are present in several cases,
but never with a P129.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Amino Acids in the Capsid Protein of Tomato Yellow
Leaf Curl Virus That Are Crucial for Systemic Infection, Particle
Formation, and Insect Transmission
*
Corresponding author. Mailing address: Istituto di
Fitovirologia Applicata, CNR, Strada delle Cacce, 73, Torino, 10135 Italy. Phone: (39)11.3977.285. Fax: (39)11.343809. E-mail:
g.accotto{at}ifa.to.cnr.it.
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