Characterization of resistance mechanism in transgenic Nicotiana benthamiana containing Turnip crinkle virus coat protein

Abstract

Two transgenic lines, of Nicotiana benthamiana expressing Turnip crinkle virus (TCV)-coat protein (CP) gene with contrasting phenotype, the highest (#3) and the lowest (#18) CP expressers, were selected and challenged with the homologous TCV. The former, the highest expresser, showed nearly five times more CP expression than the latter. Progenies of #3 and #18 lines showed 30 and 100% infection rates, respectively. The infected progenies of #3 line showed mild and delayed symptom with TCV. This is a coat protein-mediated resistance (CP-MR), and its resistance level is directly proportional to CP transgene expression. However, CP-MR of the transgenic plants was specific only for TCV but not for heterologous viruses. Newly growing leaves of those infected progenies of #3 line did not show any visible symptoms at 4-week post-inoculation (wpi) with TCV, suggesting a reversal from infection. This was confirmed by RT-PCR analysis with the disappearance of the target at 4 wpi. This is a case of RNA-mediated resistance, and a threshold level of transgene expression may be needed to achieve the silent state. To confirm the RNA silencing, we infiltrated Agrobacterium carrying TCV-CP into leaves of progenies of #3 and performed RT-PCR analysis. The results indicate that TCV-CP's suppressor activity against RNA silencing itself can be silenced by the homologous expression of TCV-CP in the transgenic plants. The transgenic plants containing TCV-CP seem to be a model system to study viral protection mediated by a combination of protein and RNA silencing.

Plant Genetic Engineering: Problems and Applications

“…Recently, using this concept the coat protein genes of several plant viruses have been transported into a number of plant species to develop resistance against viral infection. In this way the organisms engineered with genes derived from a pathogen may exhibit resistance against the pathogen itself (Vasudevan et al 2008 ) .…”

Transgenic resistance to Bamboo mosaic virus by expression of interfering satellite RNA

“…Apparently, the asymptomatic, highly resistant satBaMV transgenic plants generated here overcome several major drawbacks of CPMR, the most common way to generate virus-resistant plants (Collinge et al, 2010). CPMR has been shown to be highly resistant to viruses, such as tobamovirius, bromovirus, potexvirus, potyvirus, cucumovirus, tobravirus and tombusvirus (Abel et al, 1986;Angenent et al, 1990;Bau et al, 2003;Hemenway et al, 1988;Lawson et al, 1990;Lindbo and Dougherty, 1992;Namba et al, 1991;Shin et al, 2002a;Tumer et al, 1987;Vasudevan et al, 2008). However, some CP transgenic plants are not resistant to viral RNA infection; example viruses include TMV and Alfalfa mosaic virus (Loesch-Fries et al, 1987;Nelson et al, 1987).…”