Size Variation Among Proteins Induced by Sugarcane Mosaic Viruses in Plant Tissue

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Abstract
Virus-induced proteins, infectivity on johnsongrass (Sorghum halepense), and symptom expression on sorghum (S. bicolor) were compared for 12 isolates of maize dwarf mosaic virus (MDMV) and four isolates of sugarcane mosaic virus (SCMV). Two virus-specific proteins were identified. The capsid protein was 37 kDa and varied in size among isolates from 34.4 to 39.7 kDa. A 66-kDa protein found in infected plants of three species-sorghum, maize (Zea mays), and pearl millet (Pennisetum americanum)-was not serologically related to the capsid protein and was probably a cytoplasmic cylindric inclusion protein. This protein also varied in size (from 64.2 to 67.5 kDa) among the 16 isolates, which fell into five groups. Although host range and symptom expression on the indicator plants tended to correlate, there were enough exceptions to preclude definitive correlation of these characteristics with the size of induced proteins. The 16 isolates showed many variations in inclusion protein size, capsid protein size, host range, and symptom expression. SCMV variations may be greater than generally supposed.