The following form contents were entered on 15th Apr 97Date = 15 Apr 97 23:58:50subjectname = SarahLenhardtemail = email protectedpublish = yessubject = Biologytitle= Transgenic Rice Plants EssayTransgenicRice Plants that ExpressInsect Resistance For centuries, rice has beenone of the most important staple crops for the world and it now currently feedsmore than two billion people, mostly living in developing countries. Riceis the major food source of Japan and China and it enjoys a long history ofuse in both cultures. In 1994, worldwide rice production peaked at 530 millionmetric tons.
Yet, more than 200 million tons of rice are lost each year tobiotic stresses such as disease and insect infestation. This extreme lossof crop is estimated to cost at least several billion dollars per year andheavy losses often leave third world countries desperate for their staple food. Therefore, measures must be taken to decrease the amount of crop loss andincrease yields that could be used to feed the populations of the world. Onemethod to increase rice crop yields is the institution of transgenic rice plantsthat express insect resistance genes. The two major ways to accomplish insectresistance in rice are the introduction of the potato proteinase inhibitorII gene or the introduction of the Bacillus thuringiensis toxin gene into theplant’s genome. Other experimental methods of instituting insect resistanceinclude the use of the arcelin gene, the snowdrop lectin/GNA (galanthus nivallisagglutinin) protein, and phloem specific promoters and finally the SBTI gene.Order now
The introduction of the potato proteinase inhibitor II gene, or PINII,marks the first time that useful genes were successfully transferred from adicotyledonus plant to a monocotyledonous plant. Whenever the plant is woundedby insects, the PINII gene produces a protein that interferes with the insect’sdigestive processes. These protein inhibitors can be detrimental to the growthand development of a wide range of insects that attack rice plants and resultin insects eating less of the plant material. Proteinase inhibitors are ofparticular interest because they are part of the rice plant’s natural defensesystem against insects.
They are also beneficial because they are inactivatedby cooking and therefore pose no environmental or health hazards to the humanconsumption of PINII treated rice. In order to produce fertile transgenicrice plants, plasmid pTW was used, coupled with the pin 2 promoter and theinserted rice actin intron, act 1. The combination of the pin 2 promoter andact 1 intron has been shown to produce a high level, wound inducible expressionof foreign genes in transgenic plants. This was useful for delivering theprotein inhibitor to insects which eat plant material. The selectable markerin this trial was the bacterial phosphinothricin acetyl transferase gene (bar)which was linked to the cauliflower mosaic virus (CaMV) 35S promoter. Nextthe plasmid pTW was injected into cell cultures of Japonica rice using theBiolisticTM particle delivery system.
The BiolisticTMsystem proceeds asfollows: Immature embryos and embryonic calli of six rice materials werebombarded with tungsten particles coated with DNA of two plasmids containingthe appropriate genes. The plant materials showed high frequencyof expression of genes when stained with X-Gluc. The number of blueor transgenic units was approximately 1,000. After one week, the transgeniccells were transferred onto selection medium containing hygromycinB. After two weeks, fresh cell cultures could be seen on bombardedtissue.
Some cultures were white and some cultures were blue. Isolated cellcultures were further selected on hygromycin resistance. However, nocontrol plant survived. Then twenty plates of cells were bombarded withthe PINII gene, from which over two hundred plants were regenerated and grownin a greenhouse.
After their growth, they were tested for PINII gene usingDNA blot hybridization and 73% of the plants were found to be transgenic. DNA blot hybridization is the process by which DNA from each sample was digestedby a suitable restriction endonuclease, separated on an aragose gel, transferredto a nylon membrane, and then finally hybridized with the 1. 5 kb DNA fragmentwith pin 2 coding and 3′ regions as the probe. The results also indicate thatthe PINII gene was inherited by offspring of the original transgenic line,that the PINII levels were higher among many of the offspring and that whenPINII levels rose in wounded leaves, the PINII levels in unwounded leaves alsorose.
However, the PINII gene is not 100% effective in eliminating insectsbecause it does not produce an insect toxin, just a proteinase inhibitor. Yet, greater insect .