PLANTS TRANSFORMED WITH A CISTRON OF A POTATO VIRUS-Y PROTEASE (NIA) ARE RESISTANT TO VIRUS-INFECTION

An oligonucleotide carrying signals for translation initiation in plan ts was engineered upstream to a cDNA done containing nucleotides 5812- 7260 of the potato virus Y (PVY) genome. This fragment contains all bu t the first 100 5' terminal bases of the cistron encoding one of the P VY proteases (NIa) as well as the first 251 bases of the next cistron (NIb). Nicotiana tabacum cv. SR1 plants were transformed with this fra gment. The presence of the NIa sequences in transformed plants was det ermined by hybridization or PCR, and its expression was ascertained by reverse transcription coupled to PCR. Plants expressing NIa were self -pollinated, and the R1 kanamycin-resistant progeny were rechecked for NIa expression. Several of these plants were found to be resistant to PVY infection, inasmuch as they did not develop symptoms for at least 50 days (the duration of the experiments), and no viral accumulation could be detected in their leaves by ELISA. All of the descendents of resistant homozygous R2 plants were also resistant. Several of the pla nts transformed with the last three cistrons of PVY (bases 5812-9704; NIa-NIB-coat protein) were also resistant to PVY. None of the transfor med plants exhibited resistance to tobacco mosaic virus. Exposure of t he plants to 35-degrees-C for 48 hr prior to inoculation lowered, but did not abolish, resistance.