Jeff Schell - a Pioneer of Green Genetic Engineering
Jozef Stefaan ‘Jeff’ Schell (Juli 1935, Antwerpen - April 2003, Brussles) was a renowned and distinguished plant scientist known for his ground-breaking research in plant molecular biology and biotechnology. Schell was director at the Max Planck Institute for Plant Breeding Research from 1978 – 2000.
About Jeff Schell
In the 1970s, Schell, a pioneer of green genetic engineering, revolutionized the field with his discovery and application of Agrobacterium tumefaciens as a tool for introducing foreign DNA into plants, a technique known as plant transformation.
To publicise his findings and insights among researchers Jeff Schell travelled around the world. Lectures, consultations, and honours all over the world characterize his vita, as for example advising companies and governments, and appointments to several of the National Academies of Sciences.
In addition to honorary doctorates and honorary professorships at various universities, including Cologne, the appointment to the College de France (Paris) was a special honour. Dozens of awards including the Wolf Prize for Agriculture (1990) and the Japan Prize for Biotechnology (1998), together with Marc van Montagu, enriched his curriculum vitae.
Agrobacterium biology and its interaction with plants
Certain plant diseases, like root neck (crown) gall, are the result of infection process by bacteria. This type of plant canker (tumour-induction) affects many vegetables, flowers and fruit trees, causing uncontrolled tissue proliferation and outgrowths at the crown, the junction between root and stem. It is caused by the Agrobacterium tumefaciens, typically living in the soil. When plants are injured close to the ground, the agrobacteria penetrate them and trigger rapid tumour formation.
Studying the crown galls in detail, Schell and his colleagues discovered that Agrobacterium-induced tumours produce unusual amino acid derivatives called opines, which can be utilized by the plant infecting agrobacteria as sole nitrogen and carbon sources covering their energy requirements. This suggested that agrobacteria are capable to re-programme the plant cells, most likely, by introducing into the plants foreign genetic material (DNA, deoxyribonucleic acid) that codes for enzymes directing the synthesis of opines, as well as plant hormones (auxin and cytokinin) triggering the proliferation of tumour tissues. The cross-species gene transfer from the bacterium to the plant genome represents an evolutionary advantage for Agrobacterium, as it secures the production of unique compounds that can be specifically degraded and used both as energy sources and communication signals by agrobacteria.
Initially, the notion that Agrobacterium tumefaciens triggers plant tumour formation by integrating a foreign DNA into the plant host’s genome met with scepticism but had been soon brilliantly confirmed. Research teams of Jeff Schell and his colleague Marc van Montagu at the University of Ghent (Belgium) demonstrated that plant pathogenic agrobacteria contain a circular DNA molecule, the tumour-inducing Ti-plasmid, which is absent from Agrobacterium strains uncapable of tumour-induction. When Agrobacterium infects the plants, it transfers a segment of its Ti-plasmid, the so-called T-DNA (transferred DNA), into the nuclear genome of the host cell, whose growth is reprogrammed by the inter-species (horizontal) gene transfer so that the plant cells grow in an unregulated manner and form tumours. This phenomenon of gene transfer between agrobacteria and plants is an invention of nature itself. Ancient natural integration of T-DNA segments of Agrobacterium rhizogenes (closely related to A. tumefaciens, stimulates hairy-root formation instead of tumour) has been identified in the genomes of numerous plant species including, for example sweet potato, tobacco, and toadflax.
How the TI plasmid was repurposed
While being at the MPIPZ, Schell’s group and his former research team in Ghent led by Marc van Montagu worked out an elegant technology to use Agrobacterium as a ‘gene ferry’ and transform foreign genes of choice into plants. For the use of this natural process to produce transgenic plants, it was important to avoid the formation of tumours. De facto, the genes causing the tumour initiation could be removed and replaced by others without disturbing the T-DNA transfer mechanism. The “disarmed” T-DNA modified in this way is still incorporated into the plant genome. The transformed cells can be regenerated to form fertile transgenic plants and if a ‘desired gene’ was present on the ‘disarmed’ T-DNA, pass it on to their offspring.
This was a phenomenal technological breakthrough. Until then only genes between individuals of the same species could be combined through sexual crossing, and the desired trait could be selected through a very time-consuming process. Thus, the Agrobacterium's Ti-plasmid has been converted by knowledge-based precise modifications into a highly versatile general and essential tool for plant research that is used worldwide.
The disarmed T-DNA of optimized Ti-plasmids can now transfer any desired gene into the genome of different plant species, allowing the functions of these genes to be better studied. In addition, the T-DNA-mediated gene transfer allows for the expression of foreign proteins in plants, enabling plants being more protected against herbicides, fungal infestations, or viral diseases.
The global use of Agrobacterium T-DNA aided gene transfer has elevated plant research to a new level and opened many novel promising perspectives for sustainable agricultural production and the development of new applications in the field of plant biotechnology.
Application in agriculture
Agrobacterium has rapidly taken on a revolutionary role in agriculture as a tool for generating transgenic plants. Through the targeted introduction of foreign genes, T-DNA mediated plant transformation was used to produce plants with improved traits that are of great use in modern agriculture. Notable examples are herbicide-tolerant soybean, maize or cotton varieties. Here, genes are introduced into plants that enable them to tolerate certain herbicides, so that weeds can be controlled more efficiently without harming the crop.
Similarly, Agrobacterium assisted plant transformation has played a crucial role in the development of insect-resistant plants. This involves expressing of modified bacterial genes in plants which produce highly specific insect toxins that are not harmful for other species and applied otherwise as insecticides in practical agriculture by spraying bacterial suspension on plants. In this way, plants can develop natural protection against insect pests, reducing the need for spraying insecticides and thus enabling more environmentally friendly agricultural practices.
Another pioneering example is the development of vitamin A-enriched rice, also known as Golden Rice by the team of Swiss and German researchers Ingo Potrykus and Peter Beyer. Agrobacterium was used to introduce genes that enable the rice to produce beta-carotene, a precursor of vitamin A. This rice can help combat vitamin A deficiency, which is a health problem especially in developing countries, and improve food security.
Thanks to these applications, Agrobacterium-mediated plant transformation has had a significant impact on modern agriculture, paving the way for the development of more sustainable, resilient and nutrient-rich crops.
International competition
Such cutting-edge research was of course not without competition, and several groups were involved in it. There has been a notable patent dispute over the use of Agrobacterium-mediated plant transformation and its exploitation in in plant biotechnology. A fierce dispute arose over first rights, which was settled with MPG and Monsanto sharing the rights.
The patent dispute was resolved, and an agreement only reached in 2005, a late tribute for Jeff Schell who passed away tragically early in Brussels on 17. April 2003. Under the agreement, the Max Planck Society, its exclusive licensee Bayer Crop Science and Monsanto will cross license their respective Agrobacterium-mediated transformation technologies worldwide.
Clarification of patent claims is critical to foster innovation and accelerate technological progress while ensuring protection of intellectual property rights.
Overall, the patent dispute surrounding Agrobacterium-mediated plant transformation clearly demonstrated that the use of genetic modification in agriculture not only touches on scientific and ethical aspects, but also has a complex legal dimension that needs to be addressed to drive progress in plant biotechnology. Recent emergence of “second generation” precision plant breeding tools based on the CRISPR/CAS9 gene editing systems do not change this situation as this technology still largely relies on Agrobacterium mediated introduction of gene-editing constructs into plants. However, following precise editing of desired plant genes, the helper Agrobacterium T-DNA can be simply removed from the plant genome (i.e., by crosses or excision), and thus the end product will not be anymore “transgenic”, and its genuine identity can now be also verified by whole genome sequencing.
Plant GMOs (Genetically Modified Organisms) produced by these new technologies are thus indistinguishable from plant variants generated by any classical breeding tools, and thus no rational argument can prevent their unrestricted exploitation in agricultural production.