Full-length cDNA copies of the genomes of Grapevine virus A (GVA) and Grape
vine virus B (GVB) under the control of bacteriophage T7 promoter have been
synthesized, which were refractory to cloning in Escherichia coli. However
, both transcribed cDNAs were infectious when mechanically inoculated to Ni
cotiana plants. A full-length cDNA copy of GVB was engineered in pCass2, a
plasmid containing a partially duplicated copy of the Ca35S promoter, but w
as rather unstable in Escherichia coli. No infection of Nicotiana plants wa
s obtained following mechanical inoculation but detached Nicotiana leaves,
inoculated by particle bombardment, supported the multiplication of a GVB i
solate seemingly identical to the wild-type used for cloning. Nicotiana see
dling inoculated with sap expressed from these leaves became infected showi
ng typical GVB symptoms. Transient transcription of Ca35S driven cDNA clone
s was also detected by RT-PCR in leaves of the grapevine hybrid LN33 follow
ing inoculation by particle bombardment. The availability of infectious cDN
A clones of GVA and GVB constitutes a tool for the study of genome expressi
on and pathogenesis, and for the ultimate establishment of the aetiological
role of these viruses.