Unformatted text preview: Improving food quantity and quality Plant crops would be more valuable if they could ... survive drought, frost, etc. resist pests and diseases tolerate herbicides produce improved foods, e.g. improved nutritional content Livestock would be more valuable if they ... grew faster and were healthier produced higher quality meat, milk, eggs, etc. Agricultural Biotechnology
"Is biotechnology the answer to a hungry world's food supply?" How can biotechnology help?
Standard biotech production methods: biotech techniques for vaccines, molecular diagnosis, mass production of veterinary drugs and microbial insecticides. Genetically engineered "helper" microbes: promote plant growth by fertilizing soil, protecting from freezes, and controlling pathogens. Genetically engineered plants: transferring genes to plants confers pest, pathogen, and herbicide resistance, stress tolerance, and can modify appearance (flower color), taste, and nutritional content. Also used as bioreactors. Genetically modified animals: mice can be engineered to serve as models for human disease. livestock are diseaseresistant and produce modified foods (e.g. lactosefree milk). Produce foreign proteins in milk. Plant growthpromoting bacteria Under natural conditions, high crop yields depend on: availability of nutrients presence of beneficial microorganisms absence of pathogens Beneficial microorganisms are bacteria and fungi that (1) provide a plant growthenhancing product, and/or (2) inhibit the growth of pathogenic soil microorganisms Specific strategies develop geneticallyengineered bacteria that ... are more efficient at nitrogen fixation, lessening the current dependency on chemical fertilizers. produce hormones to stimulate plant proliferation. produce proteins, antibiotics, or enzymes that are harmful to fungal and bacterial plant pathogens. 1 Bovine growth hormone a supplement for cows Natural hormone in cows. Injection of extra bovine somatotropin (BST) into a dairy cow increases the milk yield by 2025%! The BST gene was inserted into E. coli using recombinant DNA techniques, permitting mass production & marketing by Monsanto. FDA concern: socioeconomic impact associatedcase" for Real approved for use since 1994. As the "test with recombinant drugs, it was tested extremely thoroughly. No overproduction. health effects have "geneticallyon cows or humans drinking the Lobbying strategy: been found engineered hormones" may milk. This is as expected, the hormone is identical to the cause cancer in humans recombinant DNA native substance.paranoia. Nevertheless, BST is controversial, opposed by a powerful lobby, and milk produced from these cows is banned in several countries. Why? Nitrogen fixation Nitrogen gas in the atmosphere must be converted into a form (ammonia) that can be used by plants as food. >100 million tons of fixed nitrogen are needed annually for food production. Half is produced by nitrogenfixing bacteria, synthetic fertilizers account for the other half. The use of chemical fertilizers has led to pollution problems as a result of runoff and depletion of nutrient reserves in the soil. Nitrogenase enzyme produced by bacteria Biocontrol of pathogens associated with plant roots Strategy: Modify the DNA of rhizobial bacteria so that they fix more nitrogen. Reintroduce these bacteria into soil where they become symbionts with the crop plants. Challenge: How to ensure that the engineered bacteria out compete their wildtype "relations." Phytopathogenic fungi or bacteria can reduce crop yields by 25100%. This damage is usually dealt with by the use of chemical agents which are hazardous to humans and animals. Bacteria can be engineered to produce a number of substances that limit the damage to plants by pathogens. Examples: Siderophores bind iron in the soil that fungi need to grow. Antibiotics many soil bacteria already produce substances that are toxic to other soil bacteria. The genes for many of these substances can be inserted into a single bacterial line. Enzymes certain enzymes degrade the cell walls of fungi.
2 Genetically engineered plants Most plant cells are totipotent, meaning that an entire plant can be regenerated from a single cell. Therefore, the introduction of a foreign gene (that confers a desired trait) into a plant cell can often result in a transgenic plant: a fertile plant that carries the introduced gene in all of its cells. The desired trait will be passed on to successive generations. What traits can be introduced using a single gene? insecticidal activity protection against viral infection resistance to herbicides altered flower pigmentation tolerance of environmental stresses improved nutritional quality of seed proteins improved taste and appearance (e.g. reduced discoloration) Crop Engineering Overview How are genes introduced into plant cells?
Make use of a pathogen. The bacterium Agrobacterium tumefaciens infects certain plants such as roses, grapes, and some fruit trees. It causes crown gall tumors. The bacterium infects a plant by inserting a tumorinducing plasmid into a plant cell. Some of the DNA from this plasmid becomes integrated into the plant's chromosomal DNA (the genome). (This is reminiscent of the way that bacteriophage viruses integrate their DNA into the bacterial chromosome.) Strategy: Take a natural tumorinducing plasmid from A. tumefaciens. Replace the genes that lead to tumor formation with the gene that codes for the desired trait. Place the plasmid back into A. tumefaciens and allow it to infect a plant cell. Grow the cell into a whole plant. 3 Plants that have been genetically transformed Crop Engineering Gene gun Applications of geneticallyengineered plants Insect resistance: sprayed chemical pesticides are costly ($4 billion annually) and hazardous. The bacterium Bacillus thuringiensis (BT) produces an insecticidal toxin which causes the insect to be unable to digest plant matter. It inhibits an enzyme that the insect uses to break down starch or plant proteins. The toxin does not persist in the environment and is not hazardous to mammals. Insertion of the gene for this substance in plants (tobacco, tomato, cotton, potato, rice, corn, several tree species) generally reduces the damage from insects as well as or better than spraying by chemical insecticides. Transgenic potatoes have been approved for release.
Genes for other inhibitors of insect enzymes are being developed. 4 Modification of plant nutritional content Seed storage proteins (in e.g. corn, beans, peas, soy, etc.) contain a limited number of amino acids. The nutritional value of these proteins is deficient because they lack one or more of the amino acids (lysine or methionine) essential for human health. Transgenic plants are created in which the genes that code for these proteins are modified. Transgenic soybean plants have been made that contain lysine. It is also possible to modify the type of oils present in seeds so that there are less saturated and more unsaturated oils. Transgenic animals
Traditional breeding methods have been very successful at improving desired traits in livestock, such as milk yield, wool characteristics, rate of weight gain, egglaying frequency. However, this is slow and inefficient. Also, it is difficult to develop breeding lines with multiple good traits while avoiding bad traits (genetic diseases, etc.) How can we insert specific genes into animals and propagate them from generation to generation? (1) Transfer of genes into the mammalian genome. (2a) Create breeding lines containing these genes or (2b) Create genetically identical animals (cloning). How to make a transgenic mouse Transgenic technology was developed and perfected in the laboratory mouse. Hundreds of different genes have been introduced into various mouse strains. These lines have contributed to understanding of many biological phenomena including genetic diseases. There are three methods of trangenesis in mice: (1) use a virus to inject desired genes into harvested embryos before implantation in a foster mother. How to make a transgenic mouse (2) microinjection of DNA into a fertilized egg followed by implantation in a foster mother. (This is currently the most common method.) http://www.bioitworld.com/archive/091103/russell.html These two methods have the disadvantage that only a small number of the progeny will contain the transgene i.e. selection must be performed after their birth. 5 The final method involves stem cells Standard genetic engineering methods can be used to insert genes into cultured stem cells. The cells that take up the gene can be selected and grown. Finally, these cells can be inserted into developing embryos and implanted into foster mothers. This method is particularly powerful because it permits the use of the full arsenal of genetic engineering techniques prior to implantation. Mice modified to produce Green Fluorescent Protein (GFP)
http://www.biken.osakau.ac.jp/act/images/okabeA.png Applications of transgenic mice Models for human diseases e.g. Alzheimer disease. Alzheimer disease is a degenerative brain disorder characterized by the progressive loss of abstract thinking and memory. Dense aggregates* of proteins (called "plaques" and "amyloid bodies") are found in the brains of Alzheimer victims. The principal component of these aggregates is betaamyloid protein. Families with a high incidence of Alzheimer disease are known to have mutations in the gene that codes for this protein. It is impossible to study the physical progression of the disease in humans while they are alive.
*aggregates are clumps of proteins. Think of cheese! 6 Applications of transgenic mice Models for human diseases e.g. Alzheimer disease. Transgenic cattle, sheep, goats, and pigs Transgenesis uses a variation of the microinjection method developed for mice. It has been demonstrated to be possible, though currently quite inefficient (but improving rapidly). Increasing livestock value will involve: modifying the constituents of milk to increase cheese production (more protein) hereditary resistance to bacterial, viral, and parasitic diseases Use as bioreactors: transgenic sheep and goats are created that secrete human proteins in their milk. longer term prospects include production of a human blood substitute and organs for implantation. Antigens that are involved in organ rejection can be replaced with the human version. Transgenic mice are created with the mutated amyloid protein gene. These mice display many Alzheimer diseaselike symptoms, including amyloid plaques, death of neuron cells, and memory defects. These mice are used to study the progression of the disease and the effectiveness of possible treatments. Future prospects: transgenic humans? With gene replacement therapy, one can imagine correcting defective genes (or selectively modifying certain genes) of embryonic cells before implantation. This issue has not been widely discussed but may be much more significant than issues surrounding cloning. It would allow many couples to have children without debilitating genetic diseases. (such as TaySachs and CF) http://www.bioteach.ubc.ca/Biomedicine/Th eNewMacDonaldPharm/ However, some people are concerned that this would lead to eugenics. Of course, we should assume that any modifications would be voluntary, not coerced, and uncommon because of the expense. 7 Cloning of Mammals
Nuclear transfer: (1) The nucleus (containing all the DNA) is removed from a oocyte. (2) The DNA from a donor cell is inserted into the oocyte. (3) The oocyte is implanted into a host mother and if the transfer was successful, develops to term. Success rates are low but improving rapidly. 1999: 1 in 500; 2001: 1 in 20 (for cattle) It was traditionally believed that this could work only if the transferred nucleus was taken from a pluripotent cell, like a mouse embryonic stem cell. In 1997, successful nuclear transfer was demonstrated from a differentiated cell taken from an adult mammal. Dolly was cloned by nuclear transfer of a mammary cell from an adult sheep. It has since been duplicated using cows, goats, pigs, cats, monkeys, dogs etc. and no longer seems to be specific to any particular species. It would seem that cloning humans is inevitable as it is essentially a straightforward outgrowth of previous cloning research. Commerciallyavailable cattlecloning services Enucleation Chromosomes of each egg are drawn into a needle. A pipette holds the egg still. After Enucleation Chromosomes are removed, all that remains inside the zona pellucida is cytoplasm. Transfer A skin cell, or fibroblast, from the animal to be cloned is transferred underneath the zona pellucida, where it remains separate from the egg cytoplasm. Fusion Each unit is exposed to an electric shock that fuses the skin cell with the egg cytoplasm. The skin cell's nucleus, with its genes, enters the egg cytoplasm. Embryo Seven days later the CyClonedTM embryo is ready for transfer into a recipient cow. http://www.advancedcell.com Cloning human organisms http://www.cyagra.com/index.html Cyagra is a subsidiary of Advanced Cell Technology, Inc. Eventually, embryonic cloning will become very efficient and successful i.e. there will be little risk of genetic or other defects. This seems far away now, but given the extraordinary pace of this research we must assume it will happen. At that point, will it be reasonable to implant the embryos into foster mothers and bring them to term? Is there an inherent problem with creating "delayed twins?" Zita CyCLONESTM Genesis Z and Cyagra Z Cyagra CyClonedTM the legendary Holstein cow, ConAcres HS Zita 8 ...
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This note was uploaded on 02/27/2008 for the course CHEN 1000 taught by Professor Degrazia,j during the Fall '04 term at Colorado.
- Fall '04