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8 Future Genetically Engineered Crops
Pages 405-454

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From page 405...
... The committee defines new traits as ones that have yet to be commercialized as of June 2015 even if the traits had received regulatory approval by that time or if there were published descriptions in the literature of the traits in crop plants. As discussed in Chapter 3, few genetically engineered (GE)
From page 406...
... . As discussed in Chapter 4, progress in crop improvement has been brought about by the combined use of conventional breeding and genetic engineering.
From page 407...
... and could be of great value in both genetic engineering and conventional breeding of the trait, depending on which is most efficient for the specific trait. At the level of the expression of a specific target gene, genetic engineering can bring about four types of change: reduced expression of a gene, complete loss of gene function, increased expression of a gene (including novel expression of a gene that is already in the plant in a tissue type in which it is not typically expressed)
From page 408...
... FINDING: In some cases, genetic engineering is the only avenue for creating a particular trait. That should not undervalue the importance of conventional breeding in cases in which sufficient genetic variation is present in existing germplasm collections, especially when a trait is controlled by many genes.
From page 409...
... Increased Diversity of Engineered Crops and Traits Perhaps the most dramatic change due to emerging genetic-engineering technologies is the diversity of the crops and traits that will be engineered. Although commercialized GE crops until 2015 were predominantly highproduction commodity crops (maize, soybean, and cotton)
From page 410...
... For example, oilseed crops have already been engineered to produce health-promoting polyunsaturated fatty acids through introduction of multiple genes from different species; the resulting plant oils have a composition closer to that of fish oil (Wu et al., 2005; Truska et al., 2009; Ruiz-López et al., 2012)
From page 411...
... Many potential future genetically engineered traits are predicted to be output traits, engineered specifically to change the quality of a crop. Most output traits developed in the coming decades will probably not require the use of chemical agents and should not require substantial changes in agricultural practices other than the requirement for identity protection and control of gene flow.
From page 412...
... Most GE crops commercially available when the committee was writing its report were engineered to have resistance to herbicides or to biotic stress in the forms of insects and, to a much smaller extent, viruses. Research was being conducted on other ways to combat those stressors and on ways to provide protection against sources of biotic stress that had not yet been addressed with genetic engineering.
From page 413...
... The project was publicly funded by the Netherlands government. It aimed to stimulate research on genetic engineering in Europe's social environment, which was not conducive to such innovations, and to stimulate public debate on innovative genetic-engineering approaches.
From page 414...
... . Resistance to chestnut blight has been engineered by introduction of a single gene, which encodes the enzyme oxalate oxidase, from wheat (Triticum spp.)
From page 415...
... Regulatory scrutiny should ensure that the newly introduced or ectopically expressed metabolites do not adversely affect plant quality and food safety. FINDING: A better understanding of both the nature and regulation of inducible defense pathways coupled with emerging genetic-engineering technologies could enable manipulation of complex metabolic path ways for enhancing plant resistance to disease.
From page 416...
... . FINDING: Genetic engineering can be used to develop crop resistance to plant pathogens with potential to reduce losses for farmers in both developed and developing countries.
From page 417...
... . As might be expected, not all attempts to modify insect behavior via genetic engineering are successful; wheat engineered to express a gene from peppermint (Mentha × piperita)
From page 418...
... Whether other species of insects could downregulate or even lose their natural cellular RNAi machinery and thereby become resistant to this approach is not obvious. Acquired RNAi degradation pathways seem to be one ­potential mechanism for evolved resistance.
From page 419...
... Although an understanding of the biochemistry of stress is far from complete, commercialization of some GE stress-resistant plant varieties has begun. Tolerance of Drought Plants cannot grow under severe drought, and strategies to enhance drought tolerance generally focus on better survival during drought so that if moisture returns plants can resume growth and yield loss will not be too great.
From page 420...
... Drought tolerance in plants involves multiple responses, so engineering of a single response protein may be less effective than mechanisms that can alert a plant to drought and activate a suite of responses. That may be feasible, as exemplified by a strategy that targets a receptor that responds to the drought hormone abscisic acid (ABA)
From page 421...
... As discussed in Chapter 7, most current examples of GE traits are based on one gene. As the fundamental understanding of the biochemical basis of why a specific stress inhibits plant growth or why some organisms are more resistant to a specific stress than others increases, so does the potential to use genetic engineering to enhance abiotic stress tolerance more effectively.
From page 422...
... , has always been a major goal of conventional plant breeding. In commodity crops -- such as maize, soybean, and wheat -- additional yield gain as a result of breeding is generally incremental, at an average of about 1–2 percent per year, although there have been historical exceptions when the introduction of such innovations as hybrid maize or semi-dwarf wheat and rice increased yields considerably (see Chapter 2 section "The Development of Genetic Engineering in Agriculture" and Chapter 4 section "Potential versus Actual Yield")
From page 423...
... , in agricultural production it is often economically advantageous to grow legumes with added nitrogen fertilizer to ensure reliable yields because the additional cost of the fertilizer is not prohibitive. Nitrogen-fertilizer production uses a substantial amount of natural gas -- a fossil fuel -- whereas biological nitrogen fixation does not, so engi­ neering biological nitrogen fixation has an environmental benefit.
From page 424...
... . The necessary approaches to engineering nitrogen fixation in cereals will involve synthetic biology to reengineer pathways affecting both cell biology and plant metabolism (Rogers and Oldroyd, 2014)
From page 425...
... Genetic engineering can introduce traits into alfalfa and other sources of feed that will improve digestibility and animal nutrition and reduce health risks for ruminant livestock associated with methane production. Digestibility Lignification of cell walls in forage adversely affect digestibility by ruminant animals because it restricts access of the digestive system's micro­ organisms and enzymes to cellulose and hemicellulose polymers that together make up the bulk components of both primary and secondary cell walls in plants (Ding et al., 2012)
From page 426...
... alfalfa and has to be managed to take into account the pollination method of the crop. The second potential risk associated with RL alfalfa -- one that will be relevant for many products of plant metabolic engineering -- comes from 8 At the time this report was written, Forage Genetics International was preparing to market RL alfalfa under the brand name of HarvXtra™.
From page 427...
... Triterpenes were unaffected in RL a­ lfalfa relative to their concentrations and compositions in non-GE commercial lines. Other members of the genus Medicago, to which alfalfa belongs, exhibit wide natural variation in triterpene saponin content.
From page 428...
... Although not all the biochemical reactions leading to CTs in plants are fully understood, several studies have attempted to increase CTs in plant foliage through genetic engineering. It is a complex metabolic-engineering problem because of the need to express multiple genes in a tissue in which they are not normally expressed.
From page 429...
... . The efficient release of fermentable sugars from plant cell walls is the first critical step in the conversion of lignocellulosic biomass to liquid biofuels, such as ethanol or iso-butanol, or to other industrial chemicals produced by fermentation.
From page 430...
... In trees with long generation times, genetic engineering could reduce the time to a commercial product compared with conventional breeding. Risk assessment of reduced-recalcitrance trees and grasses would probably be similar to that of RL alfalfa discussed above, with the extra issues of preventing and monitoring gene flow to native populations for indigenous species, such as switchgrass and poplar, and the long time scale for assessment of true environmental effects for many trees.
From page 431...
... FINDING: Recent advances in understanding and overcoming bio mass recalcitrance make it more likely that "second-generation" ligno­cellulosic biofuels will be developed commercially through either conventional breeding or genetic engineering.
From page 432...
... . When the genes for high phytonutrients are no longer found in germplasm collections, genetic engineering could be the only practical approach for restoring phytonutrient concentrations.
From page 433...
... . Those two micronutrients were identified previously as commonly deficient in most regions of the developing world, and such deficiencies could be addressed through genetic engineering (Zimmerman and Hurrell, 2002)
From page 434...
... However, the technology had yet to be commercialized as of 2015. Increasing Availability of Essential Amino Acids For humans and most mammals, lysine is the limiting essential amino acid in most cereal-based diets and is particularly deficient in maize grain.
From page 435...
... Because plants naturally contain anthocyanins, their concentra tions can be increased in fruits and vegetative tissues through conventional breeding if sufficient natural variation is present. However, attempts are being made to increase the concentrations of anthocyanins beyond the ranges found naturally, to introduce anthocyanins into fruits that generally lack them, and to engineer related flavonoids, such a flavonols, in fruit ­tissues through genetic-engineering technologies or by isolation of mutants (Dixon et al., 2012)
From page 436...
... The company has shown a 50–70 percent reduction in acrylamide in the GE potatoes compared with non-GE potatoes (see Chapter 5 section "Genetically Engineered Crops with Lower Levels of Toxins" for health implications)
From page 437...
... FUTURE GENETICALLY ENGINEERED CROPS, SUSTAINABILITY, AND FEEDING THE WORLD Agriculture is the largest land use on the planet, accounting for 40 percent of Earth's land area (Foley et al., 2005)
From page 438...
... . Whereas GE crops may play a role in decreasing yield gaps in ways that support sustainable intensification, it is important to point out that closing yield gaps and boosting agricultural production in many parts of the world will require improvement in agroecologically sustainable farming, irrigation, and fertilizer use (Mueller et al., 2012)
From page 439...
... For example, more nitrogen inputs may be needed to compensate for the loss of specific bacteria around the roots that deliver plant nutrients, and this could lead to nitrate leaching into the soil and production of more nitrous oxide, a potent greenhouse gas (and other geochemical cycles could be altered as well)
From page 440...
... From a similar perspective, it is worth examining GE drought tolerance carefully. This trait is considered difficult to engineer, even with emerging genetic-engineering technologies, but is generally considered desirable.
From page 441...
... The Role of New Genetically Engineered Crops and Traits in Feeding the World One of the critical questions about new traits and crops that may be enabled by emerging genetic-engineering technologies is the extent to which these products will contribute to feeding the world in the future. As noted above, Tilman et al.
From page 442...
... FINDING: Given the uncertainty about how much emerging genetic engineering technologies will increase crop production, viewing such technologies as major contributors to feeding the world must be ac companied by careful caveats. RECOMMENDATION: Balanced public investment in emerging ­genetic-engineering technologies and in a variety of other approaches should be made because it will be critical for decreasing the risk of global and local food shortages.
From page 443...
... Beyond technical hurdles, future ecological, social, and economic issues and the regulatory landscape will affect decisions in research investments by the public and private sectors and the diffusion of new discoveries. It is critical that investment in solutions involving genetic engineering not diminish investment in other technologies already shown to efficiently increase sustainable crop production and nutrition.
From page 444...
... Presentation to the National Academy of Sciences' Committee on Genetically Engineered Crops: Past Experience and Future Prospects, September 16, Washington, DC. Coulman, B., B
From page 445...
... 2011. The theory and practice of genetically engineered crops and agricultural sustainability.
From page 446...
... 2014. Remarks to the National Academy of Sciences' Committee on Genetically Engineered Crops: Past Experience and Future Prospects, September 16, Washington, DC.
From page 447...
... crop performance: Natural variation, incremental improvements and eco nomic impacts. Plant Biotechnology Journal 12:941–950.
From page 448...
... 2012. Iron biofortification in rice by the introduction of multiple genes involved in iron nutrition.
From page 449...
... Webinar presentation to the National Academy of Sciences' Committee on Genetically Engineered Crops: Past Experience and Future Prospects, March 27. Ragauskas, A.J., C.K.
From page 450...
... Webinar presentation to the National Academy of Sciences' Committee on Genetically Engineered Crops: Past Experience and Future Prospects, November 6. Sayre, R., J.R.
From page 451...
... 2009. How agricultural research systems shape a technologi cal regime that develops genetic engineering but locks out agroecological innovations.
From page 452...
... Presentation to the National Academy of Sciences' Committee on Genetically Engineered Crops: Past Experi ence and Future Prospects, December 10, Washington, DC. Welch, R.M., and R.D.
From page 453...
... 2006. Genetic basis of drought resistance at reproductive stage in rice: Separation of drought tolerance from drought avoidance.


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