Transgenic plant virus resistance mediated by untranslatable sense RNAs: expression, regulation, and fate of nonessential RNAs.

Abstract

Haploid leaf tissue of tobacco cultivars K326 and K149 was transformed with severa1 transgenes containing cDNA of the potato virus Y (PVY) coat protein (CP) open reading frame (ORF). The various transgenes containing the PVY CP ORF sequence produced (1) the expected mRNA and CP product, (2) an mRNA rendered untranslatable by introduction of a stop codon immediately after the initiation codon, or (3) an antisense RNA that was untranslatable as a result of the incorrect orientation of the PVY CP ORF behind the transcriptional promoter. Homozygous doubled haploid (DH) (diploid) plants were generated, and selfed progeny from these plants were examined. Reslstance was virus specific, functioning only against PVY. An inverse correlation between transgene-derived PVY transcript steady state levels and resistance was generally noted with lines expressing the untranslatable sense version of the PVY CP ORF. A collection of DH lines, derived from a single transformation event of a common haploid plant and isogenic for the PVY transgenes expressing untranslatable sense RNA, displayed different levels of PVY resistance. Lines with actively transcribed, methylated transgene sequences had low steady state levels of transgene transcript and a virus-resistant phenotype. These results are discussed within the context of sense suppression in plants.

Post-Transcriptional Gene Silencing of the p23 Silencing Suppressor of Citrus tristeza virus Confers Resistance to the Virus in Transgenic Mexican Lime

“…This variable response among clonal transformants carrying viral-derived transgenes has been also shown in dihaploid tobacco plants generated from single transformed haploid plants challenged with Potato virus Y (Smith et al, 1994), and in vegetatively propagated transgenic perennial ryegrass plants inoculated with Ryegrass mosaic virus (Xu et al, 2001). These observations indicate that factors other than the genetic background of the transgenic plant, such as environmental conditions or the developmental stage, play a key role in PTGS-mediated resistance (Pang et al, 1996;Kalantidis et al, 2002).…”

Application of the Human Hepatitis B Virus Core Antigen from Transgenic Tobacco Plants for Serological Diagnosis

“…The reason why hemizygous R₀ lines express much higher HBcAg levels than any other generation of plants is not clear. We speculate that it may be suppressed by host plants [34]. …”

Post-transcriptional gene-silencing and RNA interference: genetic immunity, mechanisms and applications

“…34 The ®rst indication that cosuppression operated via a mechanism that had evolved for virus-resistance came from the discovery that when transgenes expressing viral components were introduced into plants some lines were found to be virus resistant. 35,36 Subsequently, the use of viral replicon-based cDNAs as expression vectors (Amplicon 2 ) has been shown to result in reliable cosuppression. 37 The Amplicon 2 vector is an expression cassette containing the entire potato virus X (PVX) cDNA except the coat-protein gene is replaced by a target endogene (Fig 6(a)).…”