Infectious virus in transgenic plants inoculated with a nonviable, P1-proteinase defective mutant of a potyvirus

A mutant (P1-616) of the tobacco vein mottling potyvirus that contains a fo ur-codon insertion in the P1 protein coding region of the viral RNA is unab le to infect the normal host plant of the virus. Processing of the P1/HC-Pr o cleavage site does not occur during in vitro translation of the mutant vi ral RNA. When plants transformed with the P1/HC-Pro/P3 coding region of tob acco vein mottling potyvirus RNA were inoculated with P1-616, some of them became infected, although there was a delay in the production of disease sy mptoms. Virus isolated from these plants was able to infect nontransgenic p lants. Two variants of the recovered, infectious virus contained single-nuc leotide alterations in the four-codon insertion in the P1-616 genome. in vi tro translation of the variant genomic RNAs resulted in partial processing of the P1/HC-Pro cleavage site, although serological analysis of infected t issue showed complete processing in vivo. These results indicate that limit ed complementation of P1-616 occurs in the transgenic plants and that event ually there arises one or more variants of the mutant sequence that can eff ect P1/HC-Pro processing and therefore be replicated. (C) 1999 Academic Pre ss.