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Molecular Plant Pathology

Characterization of Maize Chlorotic Mottle Virus. S. A. Lommel, Department of Plant Pathology, Box 7616, North Carolina State University, Raleigh 27695-7616; T. L. Kendall(2), N. F. Siu(3), and R. C. Nutter(4). (2)(3)Department of Plant Pathology, Box 7616, North Carolina State University, Raleigh 27695-7616; (4)Pioneer Hi-Bred International, Department of Biotechnology, Box 38, Johnston, IA 50131. Phytopathology 81:819-823. Accepted for publication 22 February 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-819.

Maize chlorotic mottle virus (MCMV) is an icosahedral plant virus 30 nm in diameter, composed of a single 25-kDa capsid protein subunit and a 4.4-kb single-stranded, positive-sense genomic RNA. The genomic RNA is capped at the 5 terminus with m7GpppA, and no genome-linked protein was detected. MCMV infection produces two discrete double-stranded RNA species in infected maize plants, corresponding to single-stranded RNAs of 4.4 and 1.1 kb. The smaller double-stranded RNA corresponds to a 1.1-kb subgenomic messenger RNA that is homologous to the 3-terminal region of MCMV genomic RNA and encodes the viral capsid protein. Virion RNA directs the synthesis of 110-, 50-, 44-, 41-, 32-, and 25-kDa polypeptides in a rabbit reticulocyte lysate in vitro translation system. Only the 25-kDa polypeptide is immunoprecipitated by MCMV capsid protein antiserum. The similarities between MCMV and carnation mottle and turnip crinkle carmoviruses in their amino acid sequences, genome organization, and gene expression strategies suggest that MCMV is evolutionarily related to the carmoviruses. However, MCMV contains an additional open reading frame, does not produce a second subgenomic RNA, and has no capsid protein amino acid sequence identity with the carmoviruses. Given these distinctions, we propose that MCMV should be considered the type member of a new plant virus group.