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Review
. 2021 Oct 29;10(11):2339.
doi: 10.3390/plants10112339.

Development and Adoption of Genetically Engineered Plants for Virus Resistance: Advances, Opportunities and Challenges

Affiliations
Review

Development and Adoption of Genetically Engineered Plants for Virus Resistance: Advances, Opportunities and Challenges

Prakash M Niraula et al. Plants (Basel). .

Abstract

Plant viruses cause yield losses to crops of agronomic and economic significance and are a challenge to the achievement of global food security. Although conventional plant breeding has played an important role in managing plant viral diseases, it will unlikely meet the challenges posed by the frequent emergence of novel and more virulent viral species or viral strains. Hence there is an urgent need to seek alternative strategies of virus control that can be more readily deployed to contain viral diseases. The discovery in the late 1980s that viral genes can be introduced into plants to engineer resistance to the cognate virus provided a new avenue for virus disease control. Subsequent advances in genomics and biotechnology have led to the refinement and expansion of genetic engineering (GE) strategies in crop improvement. Importantly, many of the drawbacks of conventional breeding, such as long lead times, inability or difficulty to cross fertilize, loss of desirable plant traits, are overcome by GE. Unfortunately, public skepticism towards genetically modified (GM) crops and other factors have dampened the early promise of GE efforts. These concerns are principally about the possible negative effects of transgenes to humans and animals, as well as to the environment. However, with regards to engineering for virus resistance, these risks are overstated given that most virus resistance engineering strategies involve transfer of viral genes or genomic segments to plants. These viral genomes are found in infected plant cells and have not been associated with any adverse effects in humans or animals. Thus, integrating antiviral genes of virus origin into plant genomes is hardly unnatural as suggested by GM crop skeptics. Moreover, advances in deep sequencing have resulted in the sequencing of large numbers of plant genomes and the revelation of widespread endogenization of viral genomes into plant genomes. This has raised the possibility that viral genome endogenization is part of an antiviral defense mechanism deployed by the plant during its evolutionary past. Thus, GM crops engineered for viral resistance would likely be acceptable to the public if regulatory policies were product-based (the North America regulatory model), as opposed to process-based. This review discusses some of the benefits to be gained from adopting GE for virus resistance, as well as the challenges that must be overcome to leverage this technology. Furthermore, regulatory policies impacting virus-resistant GM crops and some success cases of virus-resistant GM crops approved so far for cultivation are discussed.

Keywords: genetically engineered (GE); genetically engineered organism (GMO); regulation of GMOs; virus-resistant transgenic crops.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Modification of three TAS genes (TAS1, TAS2, and TAS4) [55] for viral resistance. Synthetic trans-acting siRNAs (syn-tasiRNAs) designed from conserved regions of one or more viral genomes are used to replace endogenous tasiRNAs and then placed downstream of the miRNA-binding site (miRNA BS) of the TAS gene [25,26,27]. After miRNA-mediated cleavage of the transgene, the cleaved transcript is synthesized into a dsRNA template, which is processed into syn-tasiRNA by Dicer-like 4 (DCL4). Mature syn-tasiRNAs are then loaded to the RNA-induced silencing complex (RISC) to direct the targeting of transcripts from infecting cognate virus(es). Some of the proteins involved in this pathway are represented with colored ovals.
Figure 2
Figure 2
Regulatory bodies for approval of GM crops and foods in the European Union (EU), United States of America (USA), and South Africa. In the European Union and South Africa, one agency approves, while in the USA, three agencies evaluate the potential risks of GM foods. (Abbreviations: AC: Advisory Committee; DAFF: Department of Agriculture, Fisheries and Forestry; DEA: Department of Environment Affairs; DoH: Department of Health; DoL: Department of Labour; DST: Department of Science and Technology; DTI: Department of Trade and Industry; EFSA: European Food Safety Authority; EPA: Environmental Protection Agency; FDA: Food and Drug Administration; USDA: U.S. Department of Agriculture.
Figure 3
Figure 3
(A) Field resistance to CBSD in RNAi-based transgenic cassava lines in the confined field trials conducted in Namulonge research station in Uganda [125,126]; (B) Dark-brown necrotic lesions (arrow) seen on stems of CBSD-infected plants, but not on (C) in transgenic lines that exhibit resistance to CBSD; (D) Tuberous roots of transgenic cassava lines show no hard brown corky rot found in (E) non-transgenic susceptible plants; (F) siRNA accumulation in transgenic cassava for the full-length (FL)-ΔCP (pILTAB718) by northern blotting [126]. The negative control is RNA from a healthy non-transgenic (TMS60444) plant and the positive control is the original transgenic plant (718-001) used for propagation in the field trials (Modified from [122]).

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