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Title: THE MOLECULAR BASIS FOR THE ANTIGENIC DIVERSITY OF CITRUS TRISTEZA VIRUS: IMPLICATIONS FOR VIRUS DETECTION

Author
item PAPPU, H
item PAPPU, S
item LEE, R
item CAMBRA, M
item MORENO, P
item Garnsey, Stephen
item NIBLETT, C

Submitted to: Journal of Florida State Horticulture Society
Publication Type: Proceedings
Publication Acceptance Date: 5/15/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Citrus tristeza virus causes several serious diseases of citrus. Many strains of the virus exist and some are very mild while others are very severe. Development of improved management strategies for this virus would be much easier if it were possible to rapidly categorize each strain for disease severity using a simple serological test. Antibodies which react with only a single small portion of the tristeza virus coat protein (monoclonal antibodies) are being developed. Some react to most strains, while others react to only certain strains. Molecular analysis of the virus coat protein gene explains how these antibodies differ and provides information needed to use them more accurately. Because only a small change in the structure of the virus can change its reaction pattern to a single antibody, it is important to use several antibodies which react to differ parts of the virus to ensure detection of all isolates. This study clarifies the differences between two antibodies that are widely used for detection of tristeza and will allow more accurate use of these to detect single strains and strain mixtures in the future.

Technical Abstract: Citrus tristeza virus (CTV) displays a wide range of serological diversity. The CTV-specific MAb MCA13 reacts predominantly with severe strains that cause quick decline and/or stem pitting, while MAb 3DF1 reacts with most CTV strains regardless of severity. To map the antigenic determinants recognized by these MAbs, capsid protein (CP) genes of several serologically and biologically diverse strains were cloned and sequenced. Phenylalanine (Phe) at position 124 of the CP was conserved among all the MCA13-reactive strains and was replaced by tyrosine (Tyr) in MCA13-nonreactive strains. Aspartic acid (Asp) was conserved at position 2 in the CPs of all the 3DF1-reactive strains and was replaced by Glycine, in 3DF1-nonreactive strains. Mutations were introduced that altered the codons in the cloned CP genes of selected strains and were evaluated by Western blot analysis. The reactivity of MCA13 was dependent on the presence of Phe residue at position 124, while the second amino acid, Asp, was critical for reactivity of 3DF1. Point mutations in the CP gene resulting in single amino acid substitutions can drastically alter or eliminate/emergence of new serotypes of CTV, and indicates the necessity of using a combination of MAbs of differing specificities or a polyclonal antibody for the effective detection of diverse strains of CTV.