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In vitro recombinants of two nearly identical potyviral isolates express novel virulence and symptom phenotypes in plants

¹ National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, EE-12618 Tallinn, Estonia
² Department of Plant Biology and Forest Genetics, Genetics Centre, SLU, Box 7080, SE-750 07 Uppsala, Sweden
³ Department of Gene Technology, Tallinn Technical University, Akadeemia tee 23, EE-12618 Tallinn, Estonia
⁴ Department of Applied Biology, PO Box 27, FIN-00014 University of Helsinki, Finland

Correspondence
Jari P. T. Valkonen
jari.valkonen{at}vbsg.slu.se

Six novel chimeric viruses were constructed by sequentially exchanging segments of the viral genomes between the infectious cDNA clone (pPVA-B11) of Potato virus A (isolate PVA-B11) and pUFL, an almost identical infectious cDNA of PVA (isolate U) made in this study. The infectious in vitro transcripts of pUFL and pPVA-B11 caused similar severe mosaic and leaf malformation phenotypes in systemically infected leaves of Nicotiana benthamiana. In contrast, one chimera induced a unique phenotype of yellow vein chlorosis without leaf malformation with viral titres that were equivalent to those of the parental viruses. Furthermore, as opposed to the viral cDNAs from which it was assembled, one chimera showed no detectable infectivity of N. benthamiana plants. Thus, recombination of nearly identical, phenotypically similar virus genomes can give rise to new viral strains with novel virulence and symptom phenotypes, which has not previously been demonstrated with potyviruses. One chimera failed to cause systemic infection in potato plants, but, nevertheless, avirulence could not be attributed to a single genomic region. These data suggest that different parts of the potyviral genome function coordinately. The results provide novel insights into the evolution of the genus Potyvirus.

The EMBL database accession no. pUFL is AF543212.

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