Resistance Systems Related to the N Gene and their Comparison with Interferon

Summary

A probe made from a recombinant human β-interferon DNA detected specific bands in Southern blots of restriction enzyme-cleaved tobacco DNA. Specific tobacco DNA fragments also hybridized with a similar probe made from a clone of human 2′,5′-linked oligoadenylate (2–5A) synthetase. The expression of these plant genes was analysed by Northern blots using cDNA probes. Expression depended on the presence of the N gene in the tobacco cultivar. In both cases tobacco mosaic virus (TMV) infection stimulates expression. The plant β-interferon was studied further. The basal level of the relevant mRNA rapidly increases after TMV infection in N gene-carrying tobacco, and accumulation peaks 24 h after infection, whereas tobacco plants carrying the n allele are stimulated to synthesize this mRNA only about 80 h after inoculation. The plant enzyme which polymerizes ATP to antivirally active oligoadenylates was also purified from interferon-stimulated plant cells and found to resemble the human enzyme in composition and in the size of the various polypeptides, and to be serologically related to it. cDNA clones of both the plant β-interferon and the plant equivalent of 2–5A synthetase were isolated from cDNA libraries. It is concluded that the plant antiviral factor (AVF) is a type of β-interferon exerting its antiviral activity, in part, via metabolic pathways similar to those of the human interferon system.