What Is in the Crop Biotechnology Pipeline?

Although commercialized GE crops are limited in trait diversity, proof-of-concept for many other traits has been reported in laboratory experiments and small-scale field trials. These traits fit into several categories: pest resistance, agronomic performance, abiotic stress tolerance, medical applications, biofuels, and improved food, feed, and environment.      

Pest resistance traits are aimed at improving crop performance by protecting against pests. For example, researchers found a gene in the genome of a wild Mexican potato (Solanum tuberosum) variety that was subsequently engineered into cultivated potato, allowing the GE potato to survive exposure to the many races of Phytophthora infestans, the fungus responsible for the Irish potato famine (1). A native gene, Mi, from tomato was upregulated to protect the roots against root knot nematode (2). Although Europe has been reluctant to embrace engineered crops, the first field trial of GE grapes (Vitis vinifera) took place in the northern Alsace region of France in 2005. A coat protein gene from fanleaf virus was inserted into the grape rootstock (3), but not in the scion, the portion of the plant that bears fruit.

Some traits aimed at improving field performance of crops for farmers could, given responsible usage, also positively impact the environment. One key aspect of crop performance is yield. In 2001, transgenic rice plants expressing the maize proteins pyruvate orthophosphate dikinase (PPDK) and phosphoenolpyruvate carboxylase (PEPC) exhibited a higher photosynthetic capacity (35%) compared with untransformed plants (4). Another agronomic improvement focuses on nitrogen use efficiency, aimed at reducing fertilizer usage and increasing sustainability. The plant-specific transcription factor Dof1, when introduced into the model plant species Arabidopsis, increased nitrogen content by 30%, improving growth under low-nitrogen conditions (5).

Another focus is on improving abiotic stress tolerance, e.g., high salt, high and low water availability, and temperature extremes. Constitutive expression of CBF genes from the cold response pathway in GE Arabidopsis induces expression of target COR (cold-regulated) genes and enhances freezing tolerance in nonacclimated plants (6). Transgenic tomato plants overexpressing a vacuolarNa/H antiport produce fruit when grown in 200 mM sodium chloride, 40% of sea water concentration (7), and the tomato fruits display very low sodium content. The first use of GE to alter nutritional quality was the introduction of three genes into rice to create the much publicized Golden Rice variety, enriched in provitamin A (8) (see “Is Golden Rice the Only Way to Provide Vitamin A to People in Developing Countries?”). Efforts have also been successful in increasing calcium levels threefold in potato (9), as well as increasing folate levels in tomato (10).

Approaches utilizing GE plants have also focused on combating human diseases and include the development of a subunit vaccine against pneumonic and bubonic plague that is immunogenic in mice (11); a potato-based vaccine for hepatitis B, shown to raise immunological responses in humans (12); a GE pollen vaccine that reduces allergy symptoms (13); and an edible rice-based vaccine targeted at alleviating allergic diseases such as asthma, seasonal allergies, and atopic dermatitis (14) (see “Can Genetically Engineered Food Crops Be Used to Make Pharmaceuticals? Could They Contaminate the Food Supply?”).

The utilization of plants to produce alternative energy sources is a present focus of attention, given the global rise in nonrenewable energy usage and greenhouse gas emissions. One approach involves engineering the green alga, Chlamydomonas reinhardtii, to produce hydrogen gas, a clean, renewable fuel source (15). Paper waste, particularly from newspapers, is a major environmental pollutant that because of compaction remains in landfills for decades without decomposition. GE bacteria engineered with trifunctional designer cellulosomes or bifunctional systems can degrade microcrystalline cellulose and straw (16). Efforts are also aimed at improving the ability of engineered plants and microbes to process cellulosic biomass into usable biofuels (For reviews, see 17 and 18).

References:

1. Song J, Bradeen JM, Naess KS, Raasch JA, Wielgus SM, et al. 2003. Gene RB cloned from Solanum bulbocastanum confers broad spectrum resistance to potato late blight. Proc. Natl. Acad. Sci. USA 100:9128–33

2. Rossi M, Goggin FL, Milligan SB, Kaloshian I, Ullman DE, Williamson VM. 1998. The nematode resistance gene Mi of tomato confers resistance against the potato aphid. Proc. Natl. Acad. Sci. USA 95:9750–54

3. Bouquet A, Marck G, Pistagna D, Torregrosa L. 2003. Transfer of grape fanleaf virus coat protein gene through hybridization with Xiphinema index resistant genotypes to obtain rootstocks resistant to virus spread. Presented at VIII Int. Conf. Grape Genet. Breed., Int. Soc. Horticult. Sci., Acta Horticult. 603:325–36

4. Ku MS, Cho D, Li X, Jiao DM, Pinto M, et al. 2001. Introduction of genes encoding C4 photosynthesis enzymes into rice plants: Physiological consequences. Novartis Found. Symp., Rice Biotechnol.: Improv. Yield, Stress Toler. Grain Qual. 236:100–11

5. Yanagisawa S, Akiyama A, Kisaka H, Uchimiya H, Miwa T. 2004. Metabolic engineering with Dof1 transcription factor in plants: Improved nitrogen assimilation and growth under low-nitrogen conditions. Proc. Natl. Acad. Sci. USA 101:7833–38

6. Liu F-X, Tan Z-B, Zhu J-Q, Deng X-J. 2004. Arabidopsis CBF1 in plant tolerance to low temperature and drought stresses. Yi Chuan 26:394–98 (In Chinese)

7. Zhang H-X, Hodson JN, Williams JP, Blumwald E. 2001. Engineering salt-tolerant Brassica plants: Characterization of yield and seed oil quality in transgenic plants with increased vacuolar sodium accumulation. Proc. Natl. Acad. Sci. USA 98:12832–36

8. Ye X, Al-Babili S, Kloti A, Zhang J, Lucca P, et al. 2000. Engineering the provitamin A (β-carotene) biosynthetic pathway into (carotenoid-free) rice endosperm. Science 287:303–5

9. Park S, Kang T-S, Kim C-K, Han J-S, Kim S, et al. 2005. Genetic manipulation for enhancing calcium content in potato tuber. J. Agric. Food Chem. 53:5598–603

10. Diaz de la Garza RI, Gregory JF III, Hanson AD. 2007. Folate biofortification of tomato fruit. Proc. Natl. Acad. Sci. USA 104:4218–22

11. Alvarez ML, Pinyerd HL, Crisantes JD, Rigano MM, Pinkhasov J, et al. 2006. Plantmade subunit vaccine against pneumonic and bubonic plague is orally immunogenic in mice. Vaccine 24:2477–90

12. Thanavala Y, Mahoney M, Pal S, Scott A, Richter L, et al. 2005. Immunogenicity in humans of an edible vaccine for hepatitis B. Proc. Natl. Acad. Sci. USA 102:3378–82

13. Niederberger V, Horak F, Vrtala S, Spitzauer S, Krauth M-T, et al. 2004. Vaccination with genetically engineered allergens prevents progression of allergic disease. Proc. Natl. Acad. Sci. USA 101:14677–82

14. Takagi H, Hiro T, Yang L, Tada Y, Yuki Y, et al. 2006. A rice-based edible vaccine expressing multiple T cell epitopes induces oral tolerance for inhibition of Th2-mediated IgE responses. Proc. Natl. Acad. Sci. USA 102:17525–30

15. Melis A, Happe T. 2001. Hydrogen production. Green algae as a source of energy. Plant Physiol. 127:740–48

16. Fierobe HP, Mingardon F, Mechaly A, Belaich A, Rincon MT, et al. 2005. Action of designer cellulosomes on homogeneous versus complex substrates: controlled incorporation of three distinct enzymes into a defined trifunctional scaffoldin. J. Biol. Chem. 280:16325–34

17. Stephanopoulos G. 2007. Challenges in engineering microbes for biofuels production. Science 315:801–4

18. Tomey F, Moeller I, Scarpa A,Wang K. 2007. Genetic engineering approaches to improve bioethanol production from maize. Curr. Opin. Biotechnol. 18:193–99

Updated 2/16/12