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Journal of Virology, December 2002, p. 12320-12324, Vol. 76, No. 23
0022-538X/02/$04.00+0 DOI: 10.1128/JVI.76.23.12320-12324.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Department of Biological Sciences, The National University of Singapore, Singapore 117543, Republic of Singapore
Received 29 March 2002/ Accepted 15 August 2002
Hibiscus chlorotic ringspot virus (HCRSV) from naturally infected Hibiscus rosa-sinensis L. loses virulence in its experimental systemic host Hibiscus cannabinus L. (kenaf) after serial passages in a local lesion host Chenopodium quinoa. Here we report the genetic changes responsible for the loss of virulence at the molecular level. A remarkable covariation of eight site-specific amino acids was found in the HCRSV capsid protein (CP) after serial passages in C. quinoa: Val49
Ile, Ile95
Val, Lys270
Arg, Gly272
Asp, Tyr274
His, Ala311
Asp, Asp334
Ala, and Ala335
Thr. Covariation of at least three of the eight amino acids, Val49, Ile95, and Lys270, caused the virus to become avirulent in kenaf. Interestingly, the nature of the covariation was consistent and reproducible at each serial passage. These data indicate that the nonsynonymous substitutions of amino acids in the HCRSV CP after serial passages in C. quinoa are not likely to be random events but may be due to host-associated positive selection or accelerated genetic drift. The observed interdependence among the three amino acids leading to avirulence in kenaf may have implications for structural or functional relationships in this virus-host interaction.
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