Different Mechanisms Protect Transgenic Tobacco Against Tomato Spotted Wilt and Impatiens Necrotic Spot Tospoviruses

Abstract

We generated transgenic tobacco plants expressing the sense or antisense untranslatable N coding sequence of the lettuce isolate of tomato spotted wilt virus (TSWV-BL) as well as transgenic plants containing the promoterless N gene of the virus. Both sense and antisense untranslatable N gene RNAs provided protection against homologous and closely related isolates but not against distantly related Tospoviruses. These RNA-mediated protections were most effective in plants that synthesized low levels of the respective RNA species and appears to be achieved through the inhibition of viral replication. Unlike the sense RNA-mediated protection, the level of the antisense RNA-mediated protection depended on the concentration of the inoculum and the size of the test plants. Comparisons with previous results in transgenic plants expressing the intact N gene suggest that resistance to homologous and closely related TSWV isolates in plants that express low levels of the translatable N gene is due to the presence of the N gene transcript and not the N protein. In contrast, resistance to distantly related Tospoviruses is due to accumulation of high levels of the N protein and not due to the presence of the N gene transcript.

Induction of a Highly Specific Antiviral State in Transgenic Plants: Implications for Regulation of Gene Expression and Virus Resistance.

“…Finally, we suggest that the antiviral state in RNA-mediated resistant transgenic plants (de Haan et al, 1992;Lindbo and Dougherty, 1992b;van der Vlugt et al, 1992;Pang et al, 1993) and the recovered CP-producing transgenic plants function by a similar mechanism. We have previously described transgenic tobacco plants containing a TEV CP gene modified by introduction of three stop codons immediately downstream of the AUG start codon (Lindbo and Dougherty, 1992b).…”

Peptide-mediated broad-spectrum plant resistance to tospoviruses

“…resistance, which relies on altered interaction properties of the transgenically expressed coat protein interfering with the disassembly of TMV capsids (39). Interestingly, for TSWV, both types of resistance were reported to be induced by the same nucleocapsid transgene: one that requires the expression of the protein and gives low level but fairly broad-spectrum resistance, and the second that is RNA-mediated and provides high-level and highly specific resistance (8,40).…”

“…Here, presence of the viral gene product in inappropriate amounts, form or time, is thought to interfere with viral infection. However, in some cases it is difficult to distinguish between an RNA-and protein-mediated resistance (8,9). Unambiguous examples of protein-mediated virus resistance mainly concern the expression of viral coat proteins (refs.…”

Making sense (suppression) of viral RNA-mediated resistance.

“…Pang et al (1993) offered a similar explanation to account for the observation that transgenic plants expressing an untranslatable nucleocapsid protein gene from tomato spotted wilt virus (TSWV) are able to fend off TSWV infection. However, both groups noted that the degree of resistance did not correlate with the steady state levels of transgene transcript.…”

“…However, both groups noted that the degree of resistance did not correlate with the steady state levels of transgene transcript. In fact, Pang et al (1993) pointed out that the plants that showed resistance were the ones with the lowest steady state transcript levels.…”