Download PDF The Bridge: 50th Anniversary Issue January 7, 2021 Volume 50 Issue S This special issue celebrates the 50th year of publication of the NAE’s flagship quarterly with 50 essays looking forward to the next 50 years of innovation in engineering. How will engineering contribute in areas as diverse as space travel, fashion, lasers, solar energy, peace, vaccine development, and equity? The diverse authors and topics give readers much to think about! We are posting selected articles each week to give readers time to savor the array of thoughtful and thought-provoking essays in this very special issue. Check the website every Monday! The Role of Engineering and Technology in Agriculture Monday, March 8, 2021 Author: Michael A. Steinwand and Pamela C. Ronald By 2050, the global population is predicted to reach 9.7 billion. If consumption practices do not change and food continues to be wasted at alarming rates, farmers around the world will need to increase production 25–100 percent to meet the associated increase in food demand (Hunter et al. 2017). At the same time, crop yield is stagnating in many parts of the world (Ray et al. 2012), and climate change threatens the yields and nutritional content of major crops (Myers et al. 2014; Rosenzweig et al. 2014). Additionally, the range of crop pathogens and insect pests is expanding toward the global poles (Bebber et al. 2013). These challenges to sustained food security require multiple solutions encompassing social, scientific, and economic change. In this essay we highlight the current and future role of genetic technologies in advancing sustainable agriculture, reducing food insecurity around the world, diversifying the global diet, and enhancing health through the decreased use of pesticides. Technological Advances in Crop Engineering Humans have manipulated plant genomes for millennia, long before understanding the DNA underlying heritable genetics. Early domestication of wild species involved selection of characteristics such as upright vegetative structure, uniform flowering, seed retention on the plant for easier harvest, and reductions in seed dormancy and toxic chemicals in edible tissues. Geographic dispersal established locally adapted landrace cultivars. The rise in molecular genetic tools has ushered in the era of genomic breeding, wherein molecular breeding and genetic engineering have gained prominence. Crop species can now be developed in a fraction of the time and with a broader array of changes than could be achieved with conventional breeding. Crop Diversity Genetic diversity is a crucial resource for crop improvement. It can be introduced via mutagenesis using irradiation or chemical treatment, crossbreeding with related or wild populations, genetic engineering (introducing a gene from a distantly related species such as another plant species or a microbe), or gene editing (mutation or insertion of a gene at a specific locus). Plant breeding techniques may introduce valuable agronomic traits such as enhanced environmental and biotic stress tolerance to minimize yield losses and improve food nutrition and quality. Underutilized and regionally important crops, often adapted to grow on marginal lands, can be improved and grown more widely to diversify the global diet. Genomics, Proteomics, and Other “Omics” Recent technological advances and reduced costs have led to molecular “omics” studies in plant science, profiling the total complement of a biological unit such as genes (the genome) or proteins (the proteome). Whereas producing the first plant genome (of Arabidopsis thaliana) required 10 years and $100 million, a new Arabidopsis genome can now be sequenced for a few thousand dollars (Li and Harkess 2018). With modern high-throughput genome sequencing technology more economically accessible, the breadth of species with genomic data is expanding to include regionally important staple crops (e.g., cassava and finger millet) historically neglected in breeding programs of developed economies (Hendre et al. 2019). Computational correlative association studies synthesize the information in agronomic, proteomic, transcriptomic, and/or metabolomic data to reveal the genetic profiles underpinning complex traits such as flavor, drought tolerance, disease resistance, and yield. The discovery and refinement of targetable site-directed nuclease (SDN) enzymes enables precision manipulation of crop genomes (gene editing), deleting or changing DNA base pairs at specific sites to introduce genetic mutations. The RNA-guided SDN called CRISPR-Cas has become a dominant tool since 2013, when its use in gene editing was demonstrated in plant cells (e.g., Shan et al. 2013). Enhanced Disease Resistance to Address Food Insecurity Plant diseases and pests (e.g., fungi, bacteria, nematodes) reduce the annual global yield of major crops by an estimated 17–30 percent (Savary et al. 2019), with higher losses in food-insecure regions. Among many ways to address this problem are genetic engineering to add genetic material that confers resistance and mutation of the plant genes that facilitate disease susceptibility (because they either suppress plant immune responses or are required by the plant pathogen for its growth and proliferation). Underutilized and regionally important crops, adapted to grow on marginal lands, can be grown more widely to diversify the global diet. Disease susceptibility genes have been identified widely in crop species of agronomic importance and are often conserved between species. For example, breeders have used a naturally occurring mutant allele of the mildew resistance locus O (MLO) gene to confer heritable broad-spectrum immunity against powdery mildew races in susceptible barley cultivars for decades. Researchers used SDNs to edit the corresponding MLO genes in wheat (Wang et al. 2014) to generate similar resistance to the powdery mildew species infecting these crops. Reduced Use of Chemical Insecticides One of the most prevalent engineered traits across many crops, including maize, soybean, cotton, and eggplant, is insect resistance conferred by genes originating from the soil bacterium Bacillus thuringiensis (Bt). Bt insecticidal sprays have been used in organic agriculture for many years because they are specific to pests and nontoxic to humans and wildlife. Although useful, in many cases the sprays are expensive and do not prevent the insect from getting inside the plant. As an alternative to sprays, geneticists have engineered the Bt gene directly into the crop genome. On average, use of Bt maize, soybean, and cotton crops has resulted in 37 percent less insecticide use (Klümper and Qaim 2014). Recent analysis finds that widespread planting of Bt field corn also has regional insect pest-suppressive benefits to nearby non-Bt vegetable crops, which translates into fewer chemical insecticide sprays and less damage from corn borer insects (Dively et al. 2018). Plant genetic material can be added or mutated to enhance disease resistance. The cultivation of Bt-resistant crops has reduced both the use of chemical insecticides by 50 percent in India and acute pesticide poisonings in cotton growers (Kouser and Qaim 2011). In neighboring Bangladesh, the introduction of four varieties of Bt eggplant in 2014 led to a sixfold increase in net returns for farmers, in part due to a 61 percent reduction in insecticide costs (Shelton et al. 2019). Going Forward Crop genetic improvement ranges from the deletion of a few small DNA regions to the introduction of new genes or entire genetic pathways to produce new chemical compounds or agronomic traits. These genetic alterations will facilitate crop trait improvement programs. Modern biotechnologies enable scientists to introduce genetic changes that enhance disease resistance, increase yield, or enable growth on marginal lands. One exciting application is the potential to rapidly accelerate the domestication of wild plant species. A recent proof-of-concept study used a genome editing approach to increase the size and number of the ancestor of the modern tomato, so that it resembles commercial tomatoes but retains the stress tolerance traits of the wild parent (Li et al. 2018). Such efforts will likely broaden and diversify the food supply of the human diet. The targeted DNA breakages caused by SDNs may also serve as insertion points for transgenic gene clusters that enhance the nutritional content of a crop. For example, the Golden Rice trait introduces vitamin A precursor betacarotene in rice grain and has recently been approved for consumption in many countries. Production and consumption of Golden Rice will save the lives of thousands of children and young mothers suffering from vitamin A deficiency (golden rice.org). We recently demonstrated that an SDN technology can be used to insert this trait in a precise genomic target (Dong et al. 2020). Further refinement of the technique would allow for multiple traits to be stacked at targeted genomic regions, facilitating subsequent breeding. Adoption of these new biotechnology products remains limited. In 2017, 26 countries cultivated 191.7 million hectares of genetically engineered crops, with only five countries—the United States, Brazil, Argentina, Canada, and India—collectively representing 91 percent of the global transgenic crop area (ISAAA 2018). In many countries governmental frameworks for regulating genetically engineered crops are well established, whereas those governing the techniques of gene editing in crops are rapidly evolving. For example, in the European Union the EU court of justice decision stating that crops developed through genome editing must be regulated as strictly as genetically engineered products complicates EU scientific field trials of genome-edited crops and restricts farmer adoption (Faure and Napier 2019). In contrast, under its biotechnology regulations, the USDA does not regulate or have any plans to regulate genome-edited crops as long as they are not plant pests or developed using plant pests (USDA 2018). Challenges The process for commercialization of transgenic technologies and crop varieties is affected by political and socioeconomic concerns and can span decades, making it difficult to address urgent agricultural needs. Consequently, in many parts of the world, breeders and farmers do not have ready access to some genetically engineered crops. For example, while farmers in Bangladesh cultivate Bt eggplant, it is prohibited in neighboring India despite farmer demand and its clear benefits in reducing insecticide use. Similarly, organic farmers do not have access to genetically engineered crops because genetic engineering techniques are excluded from use in certified organic production (even though other types of genetic alteration such as chemical and radiation mutagenesis are permitted). There remains a need for ongoing engagement of the scientific community with diverse stakeholders, including consumers and politicians, on the challenges faced by farmers and the use of plant biotechnologies to address these challenges. Increasingly polarized political environments and fundamental changes in how information is shared have given new urgency to the problem of the disconnect between public opinion and scientific consensus on scientific topics. Acknowledgments M.A.S. was supported by a Corteva Agriscience Open Innovation program grant entitled “Gene Editing for Organic Agriculture.” P.C.R. was supported by grants from the National Science Foundation (award no. 1237975), Crary Social Ecology Fund, Foundation for Food and Agricultural Research (award no. 534683), and National Institutes of Health (GM122968). References Bebber DP, Ramotowski MAT, Gurr SJ. 2013 Crop pests and pathogens move polewards in a warming world. Nature Climate Change 3:985–88. Dively GP, Venugopal PD, Bean D, Whalen J, Holmstrom K, Kuhar TP, Doughty HB, Patton T, Cissel W, Hutchison WD. 2018. Regional pest suppression associated with widespread Bt maize adoption benefits vegetable growers. Proceedings, National Academy of Sciences 115:3320–25. Dong OX, Yu S, Jain R, Zhang N, Duong PQ, Butler C, Li Y, Lipzen A, Martin JA, Barry KW, and 3 others. 2020. Marker-free carotenoid-enriched rice generated through targeted gene insertion using CRISPR-Cas9. 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Simultaneous editing of three homoeoalleles in shexaploid bread wheat confers heritable resistance to powdery mildew. Nature Biotechnology 32:947–51. This essay was adapted from Steinwand and Ronald (2020). About the Author: This essay was adapted from Steinwand and Ronald (2020). Michael Steinwand is a postdoctoral researcher and Pamela Ronald (NAS) is a distinguished professor in the Department of Plant Pathology and the Genome Center at the University of California, Davis.