Cucumber mosaic virus-associated RNA 5. VII. Double-stranded form accumulation and disease attenuation in tobacco.
The double-stranded (ds) form of cucumber mosaic virus (CMV)-associated RNA 5 (CARNA 5), which accumulates in unusually large proportions in CMV-infected Xanthi nc tobacco plants, could be identified directly in buffer extracts of these plants via its reaction with poly(I):poly(C) or poly(A):poly(U) antisera in two-dimensional immunodiffusion tests. After infiltration of CMV-infected tobacco tissues with 4'-aminomethyltrioxalen, followed by irradiation with long-wavelength ultraviolet light, a certain proportion of the dsCARNA 5 was recovered in a crosslinked state. This showed that in all probability a major proportion of the accumulated (+) and (-) strands of CARNA 5 occurs intracellularly in ds form and that dsCARNA 5 is not an artifact of phenol extraction. In differential temperature inoculated tobacco leaves, in which virus multiplies semisynchronously, dsCARNA 5 continued to accumulate after the biological activities attributable to virus and CARNA 5 were declining steeply. In tobacco plants systemically infected with CMV strain P6, which produced very distinct symptoms in individual leaves as well as the characteristic alteration of layers of symptomatic and symptomless leaves, dsCARNA 5 was usually detected in symptomless tissues but virus was not. Also, in other tissues and organs of such plants the presence of dsCARNA 5 was generally inversely correlated with that of virus. In all likelihood, the accumulation of dsCARNA 5 is the manifestation of a mechanism which regulates disease expression and resistance in CMV-infected plants.
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Department of Botany, University of Maryland, College Park, Maryland 20742, USA.
Kaper
J M
JM