Letter | Published:

Detection of DNA complementary to pathogenic viroid RNA in exocortis disease

Naturevolume 256pages753756 (1975) | Download Citation



A LOW molecular weight (about 105 daltons) free RNA has been identified as the pathogenic agent of the exocortis disease of citrus (CEV) by Semancik and Weathers1. This minimal ‘infectious’ RNA (viroid), characterised by a highly ordered structure rich in G–C base pairs2 does not contain polyadenylate sequences3 nor can it be translated in vitro4. The CEV–RNA induces the identical symptom expression in tomato and potato as the spindle tuber viroid5, thus supporting the class relationship of these unique pathogenic RNAs. The limited genetic potential of these extremely low molecular weight pathogenic RNAs lends credence to the suggestion of host-dependent synthesis6 and the homology of the pathogenic CEV–RNA with the host genome. This relationship is supported by the detection of a CEV-like DNA, reported here, presumably resulting from the action of host polymerase7. The final pathogenic response induced by the viroid RNA might then reflect simply an aberrant expression of the host genome. These functions, resulting in pathogenic RNA synthesis by means of a DNA intermediate as well as the intimate interaction with the host cell, offer striking parallels to the oncogenic viral processes operating at a minimal level.

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  1. Department of Plant Pathology and Cell Interaction Research Group, University of California, Riverside, California, 92502

    • J. S. SEMANCIK
    •  & J. L. M. C. GEELEN


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