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Content archived on 2024-04-19

Plant molecular genetics for an environmentally compatible agriculture

Objective

The EU Biotechnology Programme (1992-94) work programme invited applications for the establishment of Projects of Technology Priority (PTP) that would secure added value for European R&D activities by helping participants in complementary projects covering different technologies of the EU supported research programme to coordinate their activities around specific objectives.
The PTP project 'Plant Molecular Genetics for an Environmentally Compatible Agriculture' was therefore conceived and implemented by AMICA to provide more scientific knowledge relevant to an environmentally sustainable agriculture, a topic of importantance for all of the member states as well as helping to enhance the continued competitiveness of European agriculture and related industries in the global market place. The project was established as a large multi-thematic programme, concentrating the scientific work programme around 15 research themes, and three local training involving 130 collaborating research teams from 11 member states. In fulfilment of the Biotechnology work programme, AMICA installed high levels of internal organisation to promote the development of the R&D infrastructure, the allocation of tasks to individual participants, the inclusion of training activities, and support to deserving groups penalized by geographic or academic isolation. Detailed final reports from each of these transnational, multidisciplinary collaborating groups of laboratories are contained elsewhere in this report. In addition to organising and managing the scientific programme of the PTP, AMICA instigated a range of management tasks which were inherent to the successful execution of the project. This PTP coordination overview will concentrate on these modalities, and highlight how added value and other benefits were realised, as well as noting some of the major scientific breakthroughs achieved during the contractual period.
Scientific Highlights
The breeding of plants for a more efficient, useful and environmentally compatible agriculture depends on creating plants with different growth habits, the ability to withstand better environmental stresses created by temperature and chemical variation, better abilities to sequester fertilisers from soils and better quality fruits and seeds for industrial processing and nutrition. The PTP has made many discoveries to enrich the fast growing pool of information that industries will use to breed new versions of crops with these improvements. Examples of some outstanding scientific success stories are detailed below:
(i) Modern breeding has given us high yielding hybrids, e.g. of maize (by crossing of some highly inbred lines). This phenomenon, known as heterosis, is well known but poorly understood. This programme attempts to correlate the capacity for high yield with the activity, or lack thereof, of certain genes.
(ii) That plant pathogenic bacteria harbour hrp (host resistance and pathogenicity) genes, some of which are highly conserved and related to genes found in animal pathogens and therefore renamed hrc (c for conserved), is not only very intriguing but the comparison also strengthens the idea that these genes are involved in a mechanism allowing the injection in the plant of chemical signals coming from the pathogenic bacteria. The importance of this work is to be measured in a medium to long-term time frame.
(iii) Plants have evolved regulated growth systems to compete with each other for sunlight. In agriculture this is not always advantageous. Transgenic tobacco plants expressing an oat PHYA gene have now been produced and shown to exhibit negative shade avoidance characteristics with reduced extension growth of stems and petioles when grown in close proximity to other plants. This manipulation of crop plant architecture has resulted in an significant increase in leaf biomass. Field trials have been carried out to advance this discovery.
(iv) The correct timing of flower formation and appropriate flower structures are a vital determinant of seed yield. Consequently flowering is being studied in detail. A gene involved in flower development has been isolated from barley. Remarkably this gene (Tumbra) shows similarity to tumour genes from humans and mice. The expression of this gene is connected to tumorous growth in plants indicating similarities between the growth of tumours in both plants and animals. The gene may be useful to help control plant cell proliferation and differentiation in plant propagation regimes.
(v) It is well known that steroids play a major influence on the development of animals. Through the analysis of a T-DNA insertion mutant of Arabidopsis affected in its growth, as well as its reactions to light, PTP research has demonstrated that certain ecdysone-like steroids (brassinosteroids) also play a major role in the regulation of a wide range of agriculturally important traits in plants (growth, defense mechanisms and reactions to light).
(vi) Plant growth is regulated by hormones such as ethylene. Manipulation of responses to hormones depends on defining the genes and pathways associated with the ethylene growth response. Studies have now demonstrated that binding of ethylene to its receptor within the plant, results in the activation of a small protein termed a G-protein. It has also been shown that the treatment of plants with ethylene leads to the initiation of a 'phosphorylation cascade' that activates steps that eventually change plant behaviour. Such observations have great significance because the small G-protein/phosphorylation cascade systems are known to be central to the control of many aspects of metabolism and development in yeast and animals, including humans. This is supported by the fact that 80% of human cancers are thought to be due to malfunctions of genes encoding small G-proteins. The plant discovery opens up ways of manipulating many aspects of plant architecture and responses.
(vii) Xyloglucan oligosaccharides (XGOs) are natural plant growth regulators. PTP research has shown that XGOs promote plant growth by 'plasticising' cell walls, induce the production of ethylene, and can move from one part of the plant to another. This knowledge is confirming these molecules as powerful initiators of changes in plant growth patterns. PTP supported work has also demonstrated how a recently discovered enzyme, xyloglucan endotransglycosylase, which plays a major role in XGO action, acts in living plant cells to modify XGO structures.
(viii) A dream of plant breeders is to be able to disrupt specific genes and replace them with new versions. This has so far proved very inefficient in higher plants. Work using Physcomitrella patens as a model species has demonstrated for the first time efficient gene disruption in plants. Disruption of genes encoding adenine phosphoribosyl transferase and the chlorophyll a/b binding protein has been achieved. Gene targeting permits the possibility of disrupting the activity of genes in order to ascertain their precise function - something vital for the research community in this era of gene discovery.
(ix) Proteins and compounds such as certain sugars or amino acids derivatives are thought to exert a synergistic effect in protecting plant cells from irreversible damage caused by different abiotic stresses. In determining how the synthesis of these compounds is regulated the PTP has identified a barley protein that is synthesised in response to cold stress. It is a useful marker for breeders to measure cold tolerance. To discover valuable genes in protecting plants against stress many Arabidopsis mutants have been isolated with altered cold acclimation and freezing tolerance. By inserting specific genes plants with a modified response to heat shock have been made. These are significant advances towards the provision of crop plants with better resistance to common stresses limiting agricultural production.
(x) In order to understand how plants respond to potassium (K+) deficiency and high salinity, PTP has characterised the pathways by which plants take up K+ and Na+. It has identified enzymes within the cell that are particularly sensitive to Na+ and show that Na+ sensitive metabolic systems are involved in intracellular signalling and regulate the pathway of active Na+ excretion under high salinity.
(xi) To modify the ability of plants to withstand drought stress, it is relevant to understand which genes respond to drought to provide protection. Sixteen have been identified in maize in the PTP project and mapped on the maize genome to explore their coincidence with drought-linked loci detected by classical genetic mapping. Also decreases in invertase have shown to be an important early response to mild water stress.
(xii) Significant advances have been made in the analysis of starch synthesis in the potato tuber with the identification of proteins involved in determining the structural features of starch. Potato plants with modified starches have been produced by manipulation of genes encoding the proteins. This information can be applied by industry to produce specific starch types suited to the needs of specialised end-users.
(xiii) In an attempt to produce 'nutrient-dense foods' the PTP has been looking into how to increase the amounts of carotenoids in certain food crops. Many appropriate genes that can be introduced into plants in order to increase the amounts and types of carotenoids have been identified. Transformation of tomato with carotenoid biosynthesis genes from bacteria has been accomplished to make tomatoes with novel carotenoids. Also our fundamental understanding of the mechanisms in plants that control the level of these pigments in plant tissues has been increased.
(xiv) Bacterial genes specifying fructans have been inserted into sugar beet and plants created that synthesise fructans. This discovery opens up new commercial potential for fructan production in this crop.
(xv) Major genetic factors regulating kernel development and the utilisation of nitrogen in cereals have been identified to aid improved seed production.
(xvi) An important objective for agriculture is to optimise the uptake of NO3 fertiliser to enable different fertiliser regimes to be practised. Genes for membrane proteins that are likely components of the high affinity nitrate uptake system of barley have been isolated. The equivalent genes have also been identified from other plant species which will enable scientists to improve the efficiency in which crop plants capture nitrate from the soil.
(xvii) The identification of the high affinity transporters for nitrate opens the way to devise transgenic plants more efficiently taking up nitrate from the soil. This can be envisaged as a strategy to reduce the needs in nitrate fertilisers for major crops.
(xviii) Plants constitutively expressing nitrate reductase are less susceptible to water stress-induced depression of nitrate assimilation. This also can contribute to devise plants requiring less nitrate for their sustained growth in semi arid conditions.
(xix) Research carried out by one of the local training networks has resulted in the development of cDNA probes that can determine the developmental phase of tree material, which will act as a valuable tool in, (i) selection of tree material for micropropagation and (ii) determination of phase status prior to rooting and weaning. The PTP has also played an important role in helping to integrate the activities of geographically isolated groups with the rest of the European plance sceince community. As a direct result of the integrated collaboration between the Irish network and PTP Scientific Programme, the first European technology transfer meeting in plant biotechnology Phytosfere '97, was successfully held at University College Dublin. This meeting was a collaborative effort between AMICA, PIP, BioResearch Ireland and University College Dublin.
(xx) As a consequence of the fruitful cooperation established between researchers in Portugal and the other members of the PTP, and of the expertise acquired in plant molecular biology, several papers are being prepared. A confidential abstract to discuss the possibility patenting of one gene sequence has been submitted to the Plant Industrial Platform.


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JOHN INNES CENTRE
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