From Mariam Mayet, African Centre for Biosafety:
Dear friends and colleagues
There have been several reports in the media recently about the development of the first genetically engineered crop developed and tested solely by Africans for Africans. Professor Jennifer Thompson and scientists at the University of Cape Town South African, in collaboration with colleagues from seed company, PANNAR Pty Ltd have reported on the development of a transgenic variety resistant to maize streak virus that could contribute to a substantial improvement in African maize yields.
The media reports on the project stress that part of the objective is to provide seed that will be sold at a minimal profit to subsistence farmers, thus removing the objection that GE technology is principally profit-driven.
The attached paper outlines the ACB's understanding of the UCT/Panna, the project which is still in its infancy, and raises important biosafety and socio-economic questions and concerns about the maize streak resistant GM maize.
African Centre for Biosafety
BRIEFING PAPER: THE UCT/PANNAR GENETICALLY ENGINEERED MAIZE RESISTANT TO MAIZE STREAK VIRUS
19 SEPTEMBER 2007
TABLE OF CONTENTS
*BACKGROUND TO THE PDR MSV MAIZE
*MAIN CONCERNS AND RECOMMENDATIONS
There have been several reports in the media recently about the development of the first genetically engineered crop developed and tested solely by Africans. Scientists at the University of Cape Town and colleagues at the South African seed company, PANNAR Pty Ltd have reported on the development of a transgenic maize variety resistant to maize streak virus. This is touted as a major advance for "African agricultural biotechnology that should contribute to a substantial improvement in African maize yields".8
In southern Africa, maize is the dominant staple food4 and per capita consumption exceeds 100kg. Maize consumption in Zambia, Zimbabwe and South Africa is highly influenced by government policy, which prioritises maize above all other crops, resulting in very few commercial substitutes, maize being the staple of low income groups, the bulk of the urban populations, in South Africa in particular. The media reports on the UCT/Pannar project stresses that part of the objective is to provide seed that will be sold at a minimal profit to subsistence farmers, thus removing the objection that GE technology is principally profit-driven.2 This paper outlines our understanding of the UCT/Pannar project and progress thus far and raises questions and concerns about the future of the maize streak resistant maize.
*BACKGROUND TO THE PDR MSV MAIZE
Maize streak virus (MSV) causes a disease of maize that produces yellow lines or streaks on the plant that reduces the plants ability to grow and to fill cobs. MSV, a geminivirus spread by the leafhopper vector, wreaks havoc on infected maize crops. Only growing leaves can be infected and the younger the plant at infection the greater the impact of the virus on the plant as a whole. The extent of MSV pathogenicity is easily measured because MSV populates mesophyll cells within precisely defined chlorotic lesions of infected maize leaves and the extent of the chlorotic surface area of infected leaves is positively correlated with the total quantity of viral DNA within the leaf.
Geminiviruses have circular single stranded DNA and a small genome that encode only a few proteins. They replicate by a rolling circle replication mechanism briefly, by initially converting single-stranded DNA (ssDNA) into double-stranded DNA (dsDNA) intermediates which then serve as templates to amplify the viral dsDNA and to produce mature ssDNA genomes. Genetically engineered virus resistance has been reported in the literature before typically by a pathogen derived resistance (PDR) strategy which is based on the insertion of resistant genes that are derived from the pathogen (virus) into the host plant.
The widely reported coat protein mediated strategy has not proved very successful for geminiviruses and the UCT/Pannar team have reported engineered resistance by encoding a C-terminal deletion of the replication associated protein (Rep) which initiates the rolling circle replication of geminiviruses. Briefly, a mutated, truncated (C-terminal deletion) form of the Rep protein gene was used to transform maize plants by biolistic transformation. The gene construct consisted of the gene inserted between the maize ubiquitin (Ubi) promoter and the Agrobacterium tumefaciens nopaline synthase (Nos) terminator in pAHC17 and co-transformed with the bar containing plasmid pAHC25.8
Normally, several copies of the Rep protein bind together to form an oligomer, which initiates replication. In the transformed plant, the transgenic protein integrates into the oligomer and inhibits replication. The reported lines have displayed constitutive gene expression and the UCT/Pannar researchers are still in the process of conducting further research in order to achieve a transformed line with single copy integration and are not at a point where there is an identified transgenic line for field trials.
*MAIN CONCERNS AND RECOMMENDATIONS
Reporting on the monitoring and characterisation of inserted gene sequences cannot be taken as an assurance that recombinant DNA methods are very precise. Transformation by particle acceleration (biolistic) is associated with multiple fragments and gene re-arrangements. , These unintended effects might be difficult to detect in the lab. Whilst targeted insertion has been shown to be quite successful in lower organism such as bacteria and viruses, such an outcome has proven more elusive in higher organisms.10 The precise insertion sites of transgenes can have an impact on the level and consistency of gene expression producing effects that may range from negligible to lethal.10
The lack of sophisticated methods for targeted insertion, especially in higher organisms9 necessitates more rigorous research into possible position effects prior to the granting of any release of transgenic organisms into the environment. Further, if transgenes behave just like naturally occurring genes, then they have the potential to be inherited in the same way and persist indefinitely in cultivated or free-living populations.
Any mixing of native and transgenic plants whether by dispersal, improper handling etc., can result in the spread of transgenes. The consequences, both ecological and evolutionary of crop-to-crop gene flow are only now beginning to be investigated in any meaningful way and the possible exposure of non-target organisms, including humans to novel proteins cannot be discounted.9 The ACB is of the opinion that molecular methods must be devised or developed in order to mitigate these unwanted effects.
Horizontal gene transfer (HGT) is the transfer of genetic material between organisms, outside the context of parent to offspring reproduction. , It is most commonly recognized as infectious transfer. HGT frequencies are now known to be much higher than originally thought. The evolution of antibiotic resistance, for example, is an indicator of the frequency of gene transfer, given that antibiotics have been used in medicine only for about 50 years.13 The intentional modification of plants could through horizontal gene transfer result in the unintentional modification of
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