GENETICALLY ENGINEERED PLANTS Momina Masood Sumaiya Gul

INTRODUCTION Engineering of crop plants is one of the rapidly expanding area of biotechnology. Genetic engineering is used to add a variety of new traits to important crops. Thousands of field trials being conducted, mostly in the United States. Six different types of traits have been introduced into plants. Twelve genetically engineered plant species have been approved for commercialization in the United States. Traditionally, most of such genetically engineered plants were tobacco, petunia, or similar species with a relatively limited agricultural application. During the past decade it now has become possible to transform major staples such as corn and rice and to regenerate them to a fertile plant

Traits Introduced in Plants Traits Genetically modified plants  Insect resistance Corn, cotton, potato, tomato.  Herbicide resistance Corn, soybeans, cotton, flax, rice, sugar beets, canola.  Virus resistance Squash, papaya, potato.  Delayed fruit ripening Tomato.  Altered oil content Canola, soybeans.  Pollen control Corn, chicory.

Genetically Engineered Species Approved for Commercialization.  Canola  Corn, including popcorn and sweet corn but not blue corn  Cotton  Flax  Papaya  Potatoes  Red-hearted chicory  Soybeans  Squash (yellow crookneck)  Sugar beet  Tomatoes, including cherry tomatoes.

 Currently, up to 85 percent of U.S. corn is genetically engineered.  91 percent of soybeans and 88 percent of cotton (cottonseed oil is often used in food products).  According to industry, up to 95% of sugar beets are now GE.  Genetic engineering of plants is much easier than that of animals. There are several reasons for this:  (1) there is a natural transformation system for plants (the bacterium Agrobacterium tumefaciens),  (2) plant tissue can redifferentiate (a transformed piece of leaf may be regenerated to a whole plant), and  (3) plant transformation and regeneration are relatively easy for a variety of plants

Plant Transformation  Alteration of the genetic makeup of plants Most Common Methods Biolistic Method A. Tumefaciens Mediated Method

The Biolistic Method Integration of DNA into Genome Shooting under high pressure Binding DNA to some particles

Shortcoming The method can cause serious damage to the cellular tissues

Agrobacterium tumefaciens  Natural plant parasites  Multiply rapidly after inducing an infection  Result in tumor formation; The “Crown galls” Their natural ability of gene transfer is manipulated for genetic engineering of plants

The Trouble Maker…or not? Transferre d DNA Virulence genes Tumor inducing Plasmid

The Ti-Plasmid

How Does It do it?

We Are More Smart!

The Two Methods

The First Genetically Modified Plant Flavr Savr

The Most Genetically Modified Ones Nicotiana tobaccumArabidopsis thaliana

Who Monitors it in USA?

Yes They Work! During testing of transgenic soybean that had been inserted with a gene from Brazil nut. The inserted gene was not detected to translate a known allergen but the allergic nature of the protein was detected in the people who were allergic to Brazil nut.

In Europe; The Assessment

Plants Allowed for Cultivation Genetically Modified MaizeAmflora

Who Regulates it in Australia?

Agricultural Impacts  Threat to Farmers and food producers  Different legislations for GM derived and conventional products  Co-existence and traceability

Genetically Modified Alfalfa Cultivation of Genetically Modified Alfalfa has been approved by United States Agriculture Secretary Tom Vilsack, as of January 2012…

The New Anti-Christ-Ghanaian Priest A Ghanaian priest has warned his followers against the consumption of Genetically Modified foods because according to him these are not only harmful but upset God’s divine plan for the world…

The Ecological Risks and Benefits of Genetically Engineered Plants  L. L. Wolfenbarger and P. R. Phifer Abstract: Discussions of the environmental risks and benefits of adopting genetically engineered organisms are highly polarized between pro- and anti-biotechnology groups, but the current state of our knowledge is frequently overlooked in this debate. A review of existing scientific literature reveals that key experiments on both the environmental risks and benefits are lacking. The complexity of ecological systems presents considerable challenges for experiments to assess the risks and benefits and inevitable uncertainties of genetically engineered plants. Collectively, existing studies emphasize that these can vary spatially, temporally, and according to the trait and cultivar modified.

Foreign Gene Expression and Challenges  Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product.  These products are often proteins, but in non-protein coding genes such as ribosomal RNA (rRNA), transfer RNA (tRNA) or small nuclear RNA (snRNA) genes.  The product is a functional RNA.  Any rational programme of plant improvement by gene transfer method must be based on how genes are organized in a plant genome and how their expression is regulated.

 DNA/RNA hybridization experiments which compare mRNA sequences on a tobacco plant show that some mRNAs are organ specific  Some are expressed in more than one organ and some are expressed in all organs.  Regions of DNA are involved in transcriptional and translational control of a gene.  The 5` prime end of promoter region is involved in initiation of transcription.  Other elements include: enhancer or silencer regions are also involved in regulation of expression.

Factors determining regulation of gene  Factors determine temporal and spatial regulation: 1. A gene must be delivered to all cells and stably maintained for transmission to progeny. 2. The promoter region must be recognized by host cell so that RNA polymerase binds.  The promoter can be regulated or constitutively expressed depending on the type of gene and desired outcome. 3. Termination and polyadenylation signal must also be provided. Thus, consideration of apropriate regulatory region of foreign gene introduced into plant cells is important. Regions include enhancers and promoters as well as terminator of transcription and 3` polyadenylation signals.

Challenges  Different promoter regions are used for different outcomes.  for strong constitutive expression the cauliflower mosaic virus 35S promoter is often used.  a highly regulated promoter responds to certain signals e.g heat, light and nutrients by turning the genes on.  the promoter for the gene encoding 1,5 bisphosphate carboxylase small subunit is light regulated, that is activated n the presence of light.  If a gene product is to be produced in a specific region of the plant, tissue specific regulatory regions must be included in the construct.  Another challenge to be considered is the codon usage.

 the codons and amino acids used by an organism, some codons are used more than others depending on the species of plants or other organism.  genes from nonplant sources especially may specify amino acids that do not match the plant’s tRNA and amino acids pools.  researchers use codon engineering: they resynthesize the donor genes if the codons or amino acids do not match the host system.  Codon engineering helps ensure that the host plant will have the appropriate tRNAs and amino acids to synthesize the protein.  To increase the production of Bacillus thuringienesis toxin by potato, tomato, rice and cotton, the Bt toxin gene has been engineered to match the host plants translation machinery and to remove incompatible sequences.

Challenges  Some genes are organ-specific. The phaseolin storage protein gene from the French bean, Phaseolus Vulgaris. This gene is normally expressed in the embryo of the developing bean seed.  the gene is expressed at very low levels in other organs.  expression of seed storage protein of soybean has been examined. The gene containing 8.5 kb of the 5` flanking sequence was expressed in immature embryos but not in leaves.  the expression of a number of genes is modulated by environmental or biological stimuli in higher plants.  expression of soybean and maize heat shock genes has been found to be heat inducible in heterologus plant tissue

Agronomically Useful Genes  Genetic engineering has a great impact on the improvement of crop species.  Plant breeding has played a major part in providing plants with better resistance to insect pests and with enhanced yields.  Some degree of success has already been realized in :  Engineering selective resistance to herbicides, herbicides inhibit plant growth by blocking the biosynthesis of important amino acids. Knowledge of the sites of inhibition has lead to the use of gene transfer strategies to engineer resistance.  Engineering resistance to viral diseases and insect pests, insect resistance in transgenic plants has been achieved through the expression in plants of the insect toxin gene of bacillus thurengenesis.

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