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TRANSGENIC PLANTS

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Transgenic plants are plants that possess gene or genes that have been transfered from a different species. They can arise by natural movement of genes between species, by cross-pollination based hybridisation between different plant species (which is a common event in flowering plant evolution), or by laboratory manipulations to insert additional genes, commonly occuring during Genetic Engineering using recombinant DNA techniques to create plants with new characteristics by artificial insertion of genes from another species. See also Genetics, List of genetic engineering topics.

Prior to the current era of Molecular genetics starting around 1975, transgenic plants including cereal crops were (since the mid 1930s) were part of conventional Plant breeding.

Transgenic varieties are frequently created by classical breeders who deliberately force hybridisation between distinct plant species when carrying out interspecific or intergeneric wide crosses with the intention of developing disease resistant crop varieties. Classical plant breeder may use use of a number of in vitro techniques such as protoplast fusion, embryo rescue or mutagenisis to generate diversity and produce plants that would not exist in nature (see also Plant breeding, Heterosis, New Rice for Africa).

These "classical" techniques (used since about 1930 on) have never been controversial, or been given wide publicity except among professional biologists, and have allowed crop breeders to develop varieties of basic food crop, wheat in particular, which resist devastating plant diseases such as rusts. Hope is one such transgenic wheat variety bred by E. S. McFadden with a transgene from a wild grass. Hope saved American wheat growers from devastating stem rust outbreaks in the 1930s.

Methods used in traditional breeding that generate transgenic plants by non-recombinant methods are widely familiar to professional plant scientists, and serve important roles in securing a sustainable future for agriculture by protecting crops from pest and helping land and water to be used more efficiently. (see also Food security, International Fund for Agricultural Development, International development)

Contents

Natural movements of genes between species.

Natural movement of genes between species, often called Horizontal gene transfer or lateral gene transfer, can also because of gene transfer mediated by natural agents such as microrganisms, viruses or mites. Such transfers occur at a frequency that is low compared with the hybridization that occurs during natural pollination, but can be frequent enough to be a significant factor in genetic change of a chromosome on evolutionary time scales, Syvanen, M. and Kado, C. I. Horizontal Gene Transfer. Second Edition. Academic Press 2002.

This natural gene movement between species has been widely detected during genetic investigation of various natural Mobile genetic elements, such as Transposons, and Retrotransposons that naturally transfer to new locations in a Genome, and often move to new species host over an evolutionary time scale. There are many types of natural mobile DNAs, and they have been detected abundantly in food crops such as rice DNA-binding specificity of rice mariner-like transposases and interactions with Stowaway MITEs.

These various mobile genes play a major role in dynamic changes to chromosomes during evolution [1], [2], and have often been given whimsical nanes, such as Mariner, Hobo, Trans-Siberian Express (Transib), Osmar, Helitron, Sleeping Princess, MITE and MULE, to emphasise their mobile and transient behaviour.

Such genetically mobile DNA contitutute a major fraction of the DNA of many plants, and the natural dynamic changes to crop plant chromosomes caused by this natural transgenic DNA mimics many of the features of plant genetic engineering currently pursued in the laboratory, such as using Transposons as a genetic tool, and molecular cloning. See also Transposon, Retrotransposon, Integron, Provirus, Endogenous retrovirus, Heterosis, Gene duplication and exon shuffling by helitron-like transposons generate intraspecies diversity in maize.

There is large and growing scientific literature about natural transgenic events in plants, such as the creation of shibra millet in Africa, and movement of natural mobile DNAs called MULEs between rice and millet [3].

It is becomming clear that natural rearrangments of DNA and generation of transgenes play a pervasive role in natural evolution. Importantly many, if not most, flowering plants evolved by transgenesis - that is, the creation of natural interspecies hybrids in which chromosome sets from different plant species were added together. There is also the long and rich history of transgenic varieties in traditional breeding. hey guys its eddy ford :P 0400579840

Deliberate creation of transgenic plants during breeding

Production of transgenic plants in wide-crosses by plant breeders has been a vital aspect of conventional Plant breeding for a century or so. Without it, security of our food supply against losses caused by crop pests such as rusts and mildews would be severely compromised. The first historically recorded interpecies transgenic cereal hybrid was actually between wheat and rye (Wilson, 1876).

Introduction of alien germplasm into common foods was repeatedly achieved by traditional crop breeders by artificially overcoming fertility barriers throughout the last century, and novel genetic rearrangements of plant chromosomes, such as insertion of large blocks of rye (Secale) genes into wheat chromosomes ('translocations'), have also been exploited widely for many decades [4].

By the late 1930s with the advent of drug Colchicine, perennial grasses were being hybridized with wheat with the aim of transferring disease resistance and perenniality into annual crops, and large-scale practical use of hybrids was well established, leading on to development of Triticosecale and other new transgenic cereal crops.

Important transgenic pathogen and parasite resistance traits in current bread wheat varieties (gene, eg "Lr9" followed by the source species) are:

Disease resistance to Leaf rust

  • Lr9 (from Aegilops umbellulata)
  • Lr18 Triticum timopheevi
  • Lr19 Thinopyrum
  • Lr23 T. turgidum
  • Lr24 Ag. elongatum
  • Lr25 Secale cereale
  • Lr29 Ag. elongatum
  • Lr32 T. tauschii

Disease resistance to Stem rust

  • Sr2 T. turgidum ("Hope" ) McFadden, E. S. (1930) J. Am. Soc. Agron. 22, 1020-1031 .
  • Sr22 Triticum monococcum
  • Sr36 Triticum timopheevii

Stripe rust

  • Yr15 Triticum dicoccoides

Powdery mildew

  • Pm12 Aegilops speltoides
  • Pm21 Haynaldia villosa
  • Pm25 T. monococcum

Wheat streak mosaic virus

  • Wsm1 Ag. elongatum

Pest resistance

  • Hessian fly
    • H21 S. cereale H23,
    • H24 T. tauschii
    • H27 Aegilops ventricosa
  • Cereal cyst nematode
    • Cre3 (Ccn-D1) T. tauschii

The intentional creation of transgenic plants by laboratory based recombinant DNA methods is more recent ( from the mid-80s on) and has been a controversial development opposed vigourously by many NGOs, and several governments, particularly within the European Community. These transgenic recombinant plants (= biotech crops, modern transgenics) are transforming agricultural productivity in those regions that have allowed farmers to adopt them, and the area sown to these crops has continued to grow globally in each of the ten years since their first introduction in 1996.

Transgenic recombinant plants are now generally produced in a laboratory by adding one or more genes to a plant's genome,and the techniques frequently called transformation. Transformation is usually acheived using gold particle bombardment or a soil bacterium (Agrobacterium tumefaciens) carrying an engineered plasmid vector, or carrier of selected extra genes.

Transgenic recombinant plants are identified as a class of genetically modified organism(GMO); usually only transgenic plants created by direct DNA manipulation are given much attention in public discussions.

Transgenic plants have been deliberately developed for a variety of reasons: longer shelf life, disease resistance, herbicide resistance, pest resistance, non-biological stress resistances, such as to drought or nitrogen starvation, and nutritional improvement (see Golden rice). The first modern transgenic crop approved for sale in the US, in 1994, was the FlavrSavr tomato, which was intended to have a longer shelf life. The first conventional transgenic cereal created by scientific breeders was actually a hybrid between wheat and rye in 1876 (Wilson, 1876). The first transgenic cereal may have been wheat itself, which is a natural transgenic plant derived from at least three different parenteral species.

Commercial factors, especially high regulatory and research costs, have so far restricted modern transgenic criop varieties to major traded commodity crops, but recently R&D projects to enhance crops that are locally important in developing counties are being pursued, such as insect protected cow-pea for Africa [5], and insect protected Brinjal eggplant for India [6].

Current global picture of modern transgenic crops

In 2005, there are more than 90 million hectares of transgenic plants created by recombinant DNA methods being grown throughout the world by some 8.5 million farmers. These farmers mostly live in the developing world. There are five general types of transgenic plants: those with genes to improve the quality of the product, those with genes to allow them to resist disease or herbivory (consumption by herbivores, usually insects), plants with genes that allow them to be resistant to the effects of specific herbicides, as well as plants with genes conferring resistance to environmental conditions that cause crop losses (extremes of cold, heat, drought,salt concentration, etc.) A developing group of transgenic plants is that of nutraceuticals, or plants designed to possess properties that make them healthier in specific ways. Examples include plants that produce higher concentrations of specific compounds like lycopene or beta carotene (see Golden rice).

An emerging class of transgenic plant increasingly created by modern methods, sometimes known as pharmacrops, aims to use plants to manufacture other products, such as pharmaceuticals and industrial chemicals. Testing of a variety of these crops has been underway for several years, and they include transgenic rice developed by a Californian company to improve oral rehydration therapy for diarrhea. In sub-Saharan Africa and parts of Latin America and Asia, diarrhea is the number-two infectious killer of children under the age of five, accounting for some two million deaths a year. A recent in Peruvian Hospital has demonstrated that specialized milk proteins lactoferrin and lysozyme made in transgenic rice plants improve the effectiveness of oral rehydration solution used to treat diarrhea. Industrial transgenic crops will be important for biofuel production and for agricultural substitutes for petrochemicals such as plastics.

Although in 2005,just over half (55%) the area sown to transgenic recombinant crops was in the United States, transgenic recombinant crops are now grown world wide. That year, the largest increase in crop area planted to these transgenics was in Brazil (9.4 million hectares in 2005 versus 5 million hectares in 2004 [7]. There has also been rapid uptake of modern transgenic cotton varieties in India. This has been associated with a dramatic improvement in the Indian cotton industry's productivity, with national average yield increases approaching a 50% improved yield per hectare above the long term average yield, because the transgenic trait Bt insect resistance has both encouraged the adoption of better performing hybrid cotton varieties, and also prevented losses to insect predation.

There is good documentation of the economic and environmental benefits of transgenic cotton in India. Economic Impact of Genetically Modified Cotton in India Comparing the Performance of Official and Unofficial Genetically Modified Cotton in India In 2006/07 it is predicted that 3.2 million hectares of modern transgenic cotton will be harvested in India (up more that 100% from the previous season)Third Consecutive Record For India Cotton Output.

Globally (in 2005),the main modern transgenic crop was soybean, widely grown in North and South America. At that time, 60% of the the worlds soybeans, 28% of the world cotton 18% of canola (rapeseed) and 14% of world corn being grown were transgenic.  That year transgenic rice (Bt) was grown also commercially for the first time on approximately four thousand hectares in Iran by several hundred farmers.

Rice is the most important food crop in the world, grown by 250 million farmers, and the principal food of the world’s 1.3 billion poorest people, mostly subsistence farmers. Commercialization of transgenic recombinant rice has huge implications for the alleviation of poverty, hunger, and malnutrition. Iran and China are the most advanced countries in area, and China has already substantially field tested modern transgenic rice in pre-production trials.

At that time most of the transgenic crops had genes either for herbicide resistance or for insect resistance. Herbicide resistance has encouraged minimum till (conservation tillage) adoption in the United States, which has benefits for the environment. The insect resistance transgenic traits (typically various Bt (= Cry) proteins from Bacillus thuringiensis species of bacteria) have greatly reduced spraying of synthetic chemical pesticides in the cotton industry, a major user of these chemicals.

Biotechnology corporations have several new transgenic crop traits in the R&D pipeline, most notably improvement in nutritional properties of vegetable oils from presence of Omega 3 polyunsaturated fatty acids, and improvements to crop water use efficiency and drought tolerance.

Regulation of transgenic plants

In the United States the Coordinated Framework for Regulation of Biotechnology governs the regulation of transgenic organisms, including plants. The three agencies involved are:

The Biotechnology Regulatory Services (BRS) program of the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) is responsible for regulating the introduction (importation, interstate movement, and field release) of genetically engineered (GE) organisms that may pose a plant pest risk. BRS exercises this authority through APHIS regulations in Title 7, Code of Federal Regulations, Part 340 under the Plant Protection Act of 2000. APHIS protects agriculture and the environment by ensuring that biotechnology is developed and used in a safe manner. Through a strong regulatory framework, BRS ensures the safe and confined introduction of new GE plants with significant safeguards to prevent the accidental release of any GE material. APHIS has regulated the biotechnology industry since 1987 and has authorized more than 10,000 field tests of GE organisms. In order to emphasize the importance of the program, APHIS established BRS in August 2002 by combining units within the agency that dealt with the regulation of biotechnology. Biotechnology, Federal Regulation, and the U.S. Department of Agriculture, February 2006, USDA-APHIS Fact Sheet

  • EPA - evaluates potential environmental impacts, especially for genes which produce pesticides
  • DHHS, Food and Drug Administration (FDA) - evaluates human health risk if the plant is intended for human consumption

Ecological risks

The potential impact on nearby ecosystems is one of the greatest concerns associated with transgenic plants but most domesticated plants mate with wild relative a some location where they are grown, and gene flow from domesticated crops (irrespective of whether they transgenic or non-transgenic) can the have potentially harmful consequences of 1. evolution of increased weediness; 2. increased likihood of extinction of wild-relatives. Weediness of hybrids created with domesticated crops is quite common. For instance in California, cultivated rye hybridises with the wild Secale montanum to produce a weed, and this has led many Californian farmers to abandon rye as a crop. [8]

Transgenes (and traits present in domesticated crop created by conventional breeding) have the potential for significant ecological impact if the plants can increase in frequency and persist in natural populations. This can occur:

  • if transgenic plants "escape" from cultivated to uncultivated areas.
  •  if transgenic plants mate with similar wild plants, the transgene could be incorporated into the offspring. 
  • if these new transgene plants become weedy or invasive, which could reduce
  • if the transgenic crop trait confers a selective advantage in natural environments

Gene flow may affect biodiversity and might affect entire ecosystems.

Pollen flow from conventional crop plants to native species also poses gene-flow derived ecological risks, as crop plants are not selected to have optimal selective advantages in natural environments, and farm fields are different to natural ecosystems. Conventional varieties also posses new traits such as pest resistance that have been deliberately transferred into the crop variety from other species.

There are at least three possible avenues of hybridization leading to escape of a transgene:

  1. Hybridization with non-transgenic crop plants of the same species and variety.
  2. Hybridization with wild plants of the same species.
  3. Hybridization with wild plants of closely related species, usually of the same genus.

However, there are a number of factors which must be present for hybrids to be created.

  • The transgenic plants must be close enough to the wild species for the pollen to reach the wild plants.
  • The wild and transgenic plants must flower at the same time.
  • The wild and transgenic plants must be genetically compatible.
  • The hybrid offspring must be viable, and fertile.
  • The hybrid offspring must carry the transgene.

Studies suggest that a possible escape route for transgenic plants will be through hybridization with wild plants of related species.

  1. It is known that some crop plants have been found to hybridize with wild counterparts.
  2. It is understood, as a basic part of population genetics, that the spread of a transgene in a wild population will be directly related to the fitness effects of the gene in addition to the rate of influx of the gene to the population.  Advantageous genes will spread rapidly, neutral genes will spread with genetic drift, and disadvantageous genes will only spread if there is a constant influx.
  3. The ecological effects of transgenes are not known, but it is generally accepted that only genes which improve fitness in relation to abiotic factors would give hybrid plants sufficient advantages to become weedy or invasive.  Abiotic factors are parts of the ecosystem which are not alive, such as climate, salt and mineral content, and temperature.

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