Emerging technology and prospects of genetic engineering to increase food production and quality Dr. Joe Kuhl Dept. of Plant, Soil, & Entomological Sciences September 12, 2012 Crop Yield Thomas Malthus (1798) concluded that agricultural production increased arithmetically, yet population increased geometrically. Historically, the increase in area cultivated could keep up with demand, not so much anymore. Yield (=edible dry mass/unit area), therefore needs to increase! 2 3 1
4 Facts: most of the dietary dry weight (and protein) for man comes from: five cereals three tuber crops several legumes two sugar crops 5 6 2
GMO = Genetically Modified Organism Also genetically modified (GM) or transgenic or genetically engineered (GE) Gruskin 2012 Marshall 2012 3
Marshall 2012 Marshall 2012 GM Plants Herbicide Tolerance Transgene provides tolerance to broadspectrum herbicides (Roundup, Liberty, ) 4
GM Plants Bt Insect-Resistant Crops Bt short for Bacillus thuringiensis, a soil bacterium whose spores contain a crystalline (Cry) protein Cry breaks down in insect gut to release a toxin (delta-endotoxin) toxic to some insects Marshall 2012 U.S. Regulatory systems Institutional Biosafety Committee (IBC) U.S. Department of Agriculture - Animal and Plant Health Inspection Service (APHIS) U.S. Environmental Protection Agency (EPA) Department of Health and Human Services - Food and Drug Administration (FDA) International agreements http://www.colostate.edu/programs/lifesciences/transgeniccrops/index.html 5
What are GM plants? Where do GM plants come from? How are GM crops different? What types of modifications are possible? How could increased yield be achieved? 6
Papaya Ring Spot Virus (PRSV) In 1992 PRSV was discovered in the Puna district of the Hawaiian Island (95% of the state s papaya was grown) PRSV traditional control strategies 1) PRSV is efficiently spread plant to plant by ~60 species of aphids, non-persistent 2) No known natural resistance to the disease - some tolerance, but this is rapidly lost 3) Use of netting is very expensive 4) Cross-protection is strain specific and not complete 5) Considerable variation exists in various strains Genetically Engineered Resistance Genetically engineered plants contain the PRSV coat protein The coat protein is used by the plant to fight against the pathogen 7
Questions to ask What plant species is modified? What gene or genes have been transferred? Where does the gene(s) come from? How does the gene function? Where is the gene expressed, what tissue and when? What trait has been modified? How is management of the crop effected? Modification Methods Gene(s) Transfer Integration of foreign gene(s) into the plant genome Trait Organisms Plants Animal Microbes Organisms Plants Animal Microbes Traditional Breeding Genetic Engineering Genes Plants Animal Microbes Genes Plants Animal Microbes 8
Genetic Engineering Transgenic Crops A transgenic crop plant contains a gene or genes which have been artificially inserted instead of the plant acquiring them through pollination. Method of introduction is key to definition, it does not matter what the resulting plant/product is. Genetic Engineering Transgene The inserted gene sequence may come from related or unrelated plant, or from a completely different species. Example: transgenic papaya produces the PRSV coat protein Example: transgenic Bt corn contains a gene from a bacterium Genetics - DNA 9
Modification Methods Gene(s) Transfer - Mechanisms Physical Biological Alternative Gene modification Gene silencing Modification Methods Gene(s) Transfer Physical Bombardment Microprojectilemediated Modification Methods Gene(s) Transfer Biological Agrobacterium tumefaciens mediated T-DNA transfer Crown Gall 10
Modification Methods Gene(s) Transfer/Modification Alternative methods: PEG-mediated protoplast transformation Electroporation mediated protoplast transformation Silicon carbide fiber Microinjections Desiccation (DNA uptake by dried embryos during rehydration) Targeted Gene Modification (TagMo) Zinc-finger nucleases, Meganuclases, TALE nucleases, DNA repair through homologous recombination Kuzma & Kokotovich 2011 Gene Silencing Exploits plant regulatory mechanism RNA Interference (RNAi) Targets specific plant gene(s) Decrease or eliminate expression May use sirna or mirna 11
Silencing of Polyphenol Oxidase Rommens et al. 2004 Modification Methods Modification Methods Gene(s) Transfer Variables: What does the gene encode for? What organism is the gene from? What is the promoter? What is the desired phenotype? Over-express, under-express Silencing: reduced or elimination of endogenous gene expression 12
Modification Methods Gene(s) Transfer Variables Variables (for each event ) Copy number Location in the plant cell Location in the plant genome Content of transferred genetic information Resulting phenotype Organisms Trait Organisms Gene(s) Transfer Plant Breeding and Testing Desired trait(s) Activity of the introduced gene Stable inheritance of the gene Avoid unintended effects on plant growth, yield, and quality (off-types) 13
Phenotypic Changes Off-types: genotype (cultivar) dependent Extensive field testing Generate sufficient material and trial under field conditions Generally, majority of transgenic material was phenotypically indistinguishable from control plants, and stable over several generations (S. Millam) GM Plants Target Areas for Improvement: 1. Biotic/abiotic stress resistance/tolerance and yield 2. Biomass feedstock for biofuels 3. Value-added: nutrition, food functionality, quality traits 4. Plant production factories therapeutics and industrial products Potato - GM Traits Disease and pest resistance Colorado potato beetle (cryiiia) Potato tuber moth (cryv, cryi Ac9) Potato cyst nematodes (chicken egg white cystatin) Viruses, e.g. PLRV and PVY (sense and antisense) Bacteria and fungi Erwinia and Phytophthora infestans 14
Late Blight Resistance Katahdin transformed with RB Song et al. 2003 Potato - GM Traits Tuber Quality Anti-bruise (down-regulate PPO) Reducing sugars (over-express ADPglucose pyrophosphorylase; silence/reduce acid invertase) Potato - GM Traits Gene silencing of vacuolar acid invertase using RNAi Bhaskar et al. 2010 15
Potato - GM Traits Nutritional value Inulin (express artichoke genes) Carotenoids (down-regulate zeaxanthin epoxidase, express Erwinia phytoene synthase) Reduced glycoalkaloid content (down-regulate Stg1) Potato - GM Traits Pharmaceutical Vaccines, drug production Industrial Starch High amylopectin and high amylose Evaluating the use of GM plants Consider GM plants on a case-by-case basis, taking into account: Nature of the introduced gene Plant parts and growth stage in which the gene product is present Toxicity or allergenicity Presence of related wild species in the vicinity http://www.colostate.edu/programs/lifesciences/transgeniccrops/index.html 16
Evaluating the use of GM plants Consider the environmental effects of alternatives to transgenic varieties: Would more harmful chemicals be applied? Would conservation tillage change? What are the probability and effects of gene escape? Are wild relatives in the region? http://www.colostate.edu/programs/lifesciences/transgeniccrops/index.html 17