Plant Biotech Blog

C Kameswara Rao
Foundation for Biotechnology Awareness and Education, Bangalore, India
pbtkrao@gmail.com

Modern Biotechnology

Modern Biotechnology provides novel goods and services using organisms or their products, applying innovative scientific and engineering principles.  Modern biotechnology found several new applications in agriculture, medicine, industrial production and environmental management, using one or more of the following procedures:

a) recombinant DNA (rDNA) technology to incorporate new genes from an organism into the genome of another organism cutting across genetic relationships, resulting in transgenic organisms (with transgenes from the bacterium Bacillus thuringiensis into crop plants, or human insulin genes into bacteria and yeasts),

b) the control of gene expression through several different means (coffee seeds without caffeine through gene silencing or enhanced production of hepatitis B antigens through somatic hybridization).

Cloning of cells, tissues, organs and organisms through culture techniques is a very important tool in biotechnological procedures, but do not constitute biotechnology per se.

Medical biotechnology aims at a) safe, effective and inexpensive medicine, b) the rapid and low cost synthesis of purer industrial products, c) restoring damaged environmental components such as soil and water, d) better crops in terms of crop health, yield, quality and reduced labor and financial inputs, to help the farmer whose focus is lower cultivation inputs, higher quality and yield. Ingenious techniques have led to innovative crops that produce nutritionally important compounds (Golden Rice with β-carotene) or therapeutically active agents (vaccines, antibodies).   

Biodiversity

Biodiversity, the short form of Biological Diversity, refers to the variety of life in all its forms, levels and combinations and includes the diversity of ecosystems, species and genes, focusing on bioresources and gene pools. 

The composition of biodiversity is not static and it has changed and will continue to change gradually, responding to numerous factors inherent in the organisms or the environment, and their interactions.  

Biodiversity Loss

Some component or the other of biodiversity was always lost as a natural process, and was replaced by new diversity components over time. 

Sudden and catastrophic changes in the habitat due to natural causes (fires, earth quakes, cyclones and floods) or human intervention (excessive use of forest resources like timber, development projects such as townships, roads, dams) cause often irreplaceable loss of biodiversity.   

Agriculture has been the single largest cause of habitat destruction and biodiversity loss.  Nevertheless, agriculture has also created new and different kinds of diversity in the same environment. 

Impact of Genetically Engineered Products on Biodiversity

The impact of medical and environmental biotech products on biodiversity and environment is largely confined to the management of effluents and pollutants from the production sites.  Environmental biotechnology actually restores degraded environmental components like soil and water. 

Agricultural biotechnology caused very contentious arguments regarding its ‘impact’ on biodiversity and the environment.  A particular Bt gene (like Cry 1 Ac) and its product have no impact if the target pest (like cotton bollworm) of the gene is not present on a plant.  Herbicide tolerance genes have no impact if an appropriate herbicide is not sprayed.  Drought, flood and salinity tolerance genes have no impact in the absence of the respective stress factors.

Activists persistently projected GE technology as a serious threat to biodiversity and the environment.  Three issues are commonly raised in this context: a) Bt corn pollen are harmful to Monarch butterflies, b) corn transgenes have introgressed into native corn varieties in Mexico and c) Bt pollen are responsible for bee Colony Collapse Disaster (CCD) in North America and Europe.  All these claims have been challenged and disproved by the scientific community.  A February 2008 publication indicates that Cry 1Ab Bt proteins do not affect the performance of bumble bees in any manner.

Crop Variety Diversity and Genetically Engineered crops

The dimensions of crop diversity are reflected in the vast numbers of varieties of globally important crops such as rice (about 1,000,000 varieties), wheat (70,000), corn (45,000), and many others.  As crops are bred to improve over the existing varieties, the new varieties of a crop, preferred by the farmers and the consumers, displaced the older ones, resulting in a continuous reduction in the number of older varieties under cultivation.  The present day farmers prefer genetically engineered (GE) varieties of crops, which replace the conventional varieties.

Anti-tech activists argue that GE crops will destroy the existing gene pools of crops, since discontinued cultivation results in the disappearance of genetic traits that may prove to be valuable in future.  There are hundreds of thousands of crop seed collections in different institutions which may contain genes for some valuable traits.  Even though these seeds may not germinate now to produce plants needed for research, modern techniques of molecular biology could be used to rescue any useful genes from them. 

A comprehensive report on the impact of agricultural biotechnology on biodiversity from the Bern University’s Botanic Garden (2004) reiterated that the introduction of GE crop varieties does not represent any greater risk to crop genetic diversity than the varieties of conventional agriculture.  GE actually increases crop diversity by adding new varieties. 

Crop Field Diversity

Another aspect related to crop diversity is crop field diversity, constituted by a) the insects colonizing on the crop plants, b) other insects, birds and small animals that feed on the former, c) the pathogens of the crop and d) the weeds in the crop fields. 

Pest or pathogen tolerant GE crops affect only the target pest or pathogen.  They reduce application of chemical pesticides that harm non-target organisms and enhance populations of beneficial insects, facilitating visits by birds preying on insects, thus restoring crop field biodiversity that was restrained by excessive inputs of agricultural chemicals.  Reduced handling of chemical pesticides reduces the risk farm workers face from exposure to them. 

The composition of weeds in a given crop field depends upon the crop and agricultural practices, as for example the weeds in a rice field are not necessarily the same as those in sugarcane or corn or pulse crop fields in the same area.  Weeds cause over 30 per cent crop yield losses and so need to be removed effectively and scientifically.    

Activists insist that the weeds in crop fields are valuable components of diverse diets and that they are important as medicinal plants and so herbicides should not be used.  The crop field weeds are common species that are found easily in the same area and there is no special merit in them to be protected at the expense of crop productivity.

Anti-tech activists have also contended that the genes from GE crops would get incorporated into the wild and weedy varieties of the crops, through ‘gene flow’ and result in ‘super weeds’.  Nothing, in centuries of agricultural experience, or about 15 years’ of research and regulatory processing of several GE crops in different countries, has indicated such a possibility.  A ten year long experiment in the UK has shown that pest tolerant and herbicide tolerant GE crops have actually perished earlier than their non-GE counter parts.  None escaped into the environment to become a super weed.  Crops are heavily pampered with inputs and care, which are unavailable outside a crop field. 

A peer reviewed report of March 2007 stated that no aspect of credible science based on ten years of field research and commercial cultivation has indicated that GE crops have harmed biodiversity or the environment. 

November 28, 2008

C Kameswara Rao
Foundation for Biotechnology Awareness and Education, Bangalore, India
pbtkrao@gmail.com

There are two kinds of ‘gene flow’, the natural processes of transfer of genes from one species/variety to another.  Gene flow through natural interspecific or intervarietal hybridization mediated by pollen is ‘vertical gene flow’, which results in the transfer of entire genomes.  The genes are transferred from the parent to the offspring and express only in the next generation, the offspring. 

The other kind is ‘horizontal or lateral gene flow’, which is a rare natural biological event that transfers a few genes at a time from one species to an unrelated species, without involving sexual reproduction. 

Crossability Barriers and Reproductive Isolation

Species and even their varieties do not cross with each other freely.  They are reproductively isolated, with their identity being maintained through several genetically controlled physical and/or physiological crossability (reproductive) barriers.  Species and varieties differ in chromosome number and structure, and genetic constitution, which are often serious impediments to the fertility of the offspring of hybrid crosses.  Reproductive barriers may also operate at one or more stages of pollen germination, viability, fertilization, embryo development and seed germination.  When reproductive isolation from reproductive barriers is strong, even persistent attempts at artificial hybridization have failed.  When such restrictions are weak, natural intervarietal or interspecific hybridization and gene transfer may occur. Even intergeneric gene transfer such as known from wheat (Triticum aestivum) to a distant wild relative (Aegilops peregrina) is a possibility, though extremely rare.  Repeated (back) crossing with the donor parent results in introgression, the stable incorporation of genes from one differentiated gene pool into another.

Biosecurity of Genetically Engineered Products

Biosecurity, the safety of genetically engineered (GE) products as food and feed and the safety of the environment, is a matter of concern both for the biotechnologists and the critics.  It was the scientists, not the anti-GE activists, who first thought of biosecurity issues, investigated the extent of risk and devised means to mitigate any possible risk.  Before commercialization, each GE product is subjected to a very lengthy and stringent biosecurity regime and only when the product is found to be safe and has a favorable risk-benefit ratio; it is released for public use. 

The opponents of GE (transgenic) crops and products made gene flow a contentious issue and raised several biosecurity concerns in their anti-GE arguments. 

Vertical gene flow

The apprehension is that pollen from the transgenic crops pollinate non-GE varieties (gene escape) causing genetic contamination or pollution.   According to the anti-tech activists such an event would cause untold horrors to the crops and the environment.  The activists argue that the non-target organisms would be affected and the transgenics would become super weeds.

Issues of gene flow should take into consideration several factors related to the reproductive biology of the species involved.  Vertical gene flow requires a) populations of two different varieties/species that grow together in the same geographical area (sympatric), b) they should be synchronous in flowering time, pollen viability and stigma receptivity, and c) be genetically compatible allowing random mating (panmictic) between the two populations, which means that there are no reproductive barriers preventing hybridization or at least that they are weak. 

The means of pollination, extent of natural cross-pollination, duration of pollen viability and stigma receptivity, extent of cross-fertilization, embryo survival and seed and fruit set are the critical events in gene flow.   The degree of fertility of the hybrids depends upon the degree of genetic compatibility.  Analysis of the hybrids would indicate the extent of gene transfer.  If the transferred genes add to the competence of the species/variety (adaptive value), and if there is repeated back crossing with the donor parent, the genes will be fixed in the population (introgressed) which in course of time differentiates as a new variety or even a new species.

Gene flow can occur between transgenics and the isogenic varieties of a crop, to the same extent as was happening earlier between non-transgenic populations of that crop.  Transgenes do not promote promiscuity.  Unintended transgenic hybrids resulting from gene flow from GE crops to wild or weedy relatives is possible, but cannot easily or routinely occur.   

Hybridization experiments have shown that intercrossing among the indica varieties of rice was 3.9 per cent and among japonica varieties it was 3.6 per cent, while practically there was no intercrossing between indica and japonica varieties.  Gene flow of an herbicide resistant gene from a cultivated rice variety to a weedy rice variety was 0.011 to 0.046 per cent and from a cultivated variety to a wild variety was 1.21 to 2.19 per cent. 

A comparative analytical study of GE and non-GE corn has shown that the transgenic content of a non-GE population was 0.9 per cent at 10 m from the GE population.   The claim that corn transgenes have introgressed into native corn varieties in Mexico was disproved.

In Canola, the presence of an herbicide resistant gene in a non-GE population was 0.1 per cent at 5 m, 0.02 per cent at 10 m and zero at more than 15 m distance, from the GE variety.

Since the conditions under which these experiments were conducted do not exist in nature, the possibility of gene flow and of the impact of such an event would be even less. 

The transgene, such as herbicide resistance in rape seed, may introgress and the gene may even persist for some time in a very small fraction of the population for a while.  A recent report in Molecular Ecology (October 2007) on transgenic herbicide tolerance genes in two species of Brassica indicates that such individuals have intermediate genome structure and their frequency rapidly decreases from about 44 per cent to 2.5 per cent in three years.  They have reduced pollen viability and reduced male fertility. 

The mere presence of a transgene in a plant is of no consequence. The question is what is the impact of few miniscule weedy populations with rapidly deteriorating vigor in agronomic terms? A Bt gene has no impact if the intended pest is not present and an herbicide tolerant gene is of no consequence if an appropriate herbicide is not sprayed.  The gene should introgress and should impart an advantage to the recipient population over the others which do not have the transgene. 

Horizontal gene flow

The other set of anti-GE arguments relate to the horizontal or lateral gene flow, raised in the context of antibiotic resistance genes used as selectable markers in GE technology.  It is argued that these genes would be taken up by soil pathogens which would become resistant to the antibiotics, and people infected by them cannot be cured by that antibiotic, leading to incurable diseases and death.

In horizontal gene flow which does not involve sexual reproduction and bypasses reproductive isolation, the few genes transferred can express in the same cell generation.  In nature, horizontal gene flow is a fundamentally prokaryotic (organisms with no nucleus or cell organelles such as bacteria) phenomenon.   Other natural examples of horizontal gene flow relate to endoparasites and their hosts, which share several genes as a result of millions of years of co-habitation and co-evolution. 

Horizontal gene flow occurs through one of five different biological processes known as transformation, conjugation, transfection, lysogenization and transduction.  Recombinant DNA (rDNA) technology that involves transformation is a good example of artificial horizontal gene transfer that makes transgenics possible irrespective of genetic relationship. 

The issue of horizontal transfer of antibiotic resistance marker genes from transgenic plants to bacteria was discussed in depth at an international symposium on the Biosafety of GE organisms in 2000.  The consensus was that such an event is very unlikely and even if it happens it would not contribute significantly to the horizontal spread of the genes in question, for three reasons: a) the antibiotic resistance genes are already widespread in bacterial populations, b) there was no experimental evidence for horizontal gene transfer from plants to bacteria, and c) horizontal gene transfer events from transgenic plants to bacteria have not been detected.  There is no change in this position till to date.

A recent paper in Transgenic Research (June, 2007) concluded, supported by numerous studies, most of which are commissioned by some of the very parties that have taken a position against the use of antibiotic selectable marker gene systems, is that there is no scientific basis to argue against the use and presence of selectable marker genes in transgenic plants.

November 28, 2008

Failures of Austrian GMO Study

Experts are picking up scientific errors in a GMO corn safety study publicised recently by the Austrian government. Austrian investigators are being strangely silent about a disturbingly low survival rate of mouse pups in their laboratories. See the links above to GMO Pundit blog for details.