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Physiologie végétale
trends in plant science research news
Physiologie végétale Highlights of the third general meeting of the French Society of Plant Physiology* included reports on light-induced signal transduction, use of the green fluorescent protein (the presentation was so enthralling that the speaker was asked to repeat his talk later that same day – an almost unprecedented event at a scientific meeting) and the latest data about the involvement of lipo-chito oligosaccharides in nodule formation in legumes. One of the factors behind the tremendous progress achieved in the plant sciences over the last decade has been the continuing improvement in communication between scientists. This meeting continued the good work, and was an ideal forum for intraand interdisciplinary exchange of ideas, with a strong field of international speakers.
programme, only around 200 of the estimated 20 000 genes had been characterized. Now, more than 30 000 ESTs, corresponding to approximately 12 000 genes, have been placed in the public databases. In parallel with the EST programme, the Arabidopsis genome sequencing project now has the sequence of almost 20% of the Arabidopsis genome. Given the significant conservation of gene order and function between Arabidopsis and other plant species, the information provided by these programmes will undoubtedly continue to
revolutionize plant biology and lead to the improvement of commercially important crops. Hervé Vaucheret [Institut National de la Recherche Agronomique (INRA), Versailles, France] spoke on the recent progress in characterizing the mechanism of transgeneinduced gene silencing in plants. It is now well established that gene silencing occurs at both the transcriptional and post-transcriptional levels. In addition, it has been found that a diffusible factor mediates the systemic transmission of post-transcriptional silencing. The
Gene structure, regulation and function
Michel Delseny (University of Perpignan, France) and G. Murphy (John Innes Centre, Norwich, UK) presented the results of their ground-breaking work on the Arabidopsis expressed sequence tag (EST) and gene sequencing projects. At the outset of the EST
Photos courtesy of J-C. Pech.
*General Meeting of the French Society of Plant Physiology, Toulouse, 1–3 December 1997. Further information on this meeting can be found in a proceedings volume entitled Plant Sciences 1997 available at the Laboratoire du Métabolisme, Institut National de la Recherche Agronomique (INRA), Route de Saint Cyr, F-78026, Versailles Cedex France. Copyright © 1998 Elsevier Science Ltd. All rights reserved. 1360 - 1385/98/$19.00
study of transgene-induced silencing should provide important clues in the understanding of natural plant defence mechanisms that act at the DNA or RNA level to stabilize the genome and protect plants against pathogens. Nicole Chaubet-Gigot (Institut de Biologie Moléculaire des Plantes, Strasbourg, France) described the efforts of her group to elucidate the molecular mechanisms involved in the induction of gene expression at the G1–S transition phase of the plant cell cycle. Through the study of two alternative model genes, those encoding histones and the two subunits of ribonucleotide reductase, the group has developed a model for the sequential induction of genes during the transition. Functional and structural analysis of the histone promoters indicate that transcriptional activation of some histone genes at the G1–S transition is mediated by the modification of prebound factors, April 1998, Vol. 3, No. 4
119
trends in plant science research news probably through protein phosphorylation. Ribonucleotide reductase and histone promoters contain different cis-elements, suggesting that the two model genes are induced by two different regulatory mechanisms. Signal perception and transduction
Knowledge of the ethylene signal-transduction pathway is the most advanced among the plant hormones, and Joe Ecker (University of Pennsylvania, Philadelphia, USA) presented his findings in the area. Progress has come about largely as a result of a simple developmental growth response known as the ‘triple response’. Several classes of mutants altered in ethylene responses have been identified, and a genetic framework has been proposed for the action of the corresponding genes (see also Ref. 1). In addition, G. Neuhaus (University of Freiburg, Germany) described the progress being made in our understanding of the molecular events underlying light-induced signal transduction. One of the elements stressed was the continuous crosstalk between different components in the signalling pathways. The symbiotic interaction between legumes and Rhizobium is a classical example of crosstalk between host plant and bacterium. Michael Schultze [Centre National de la Recherche Scientifique (CNRS), Gif-surYvette, France] described how the molecular dissection of Nod factors is helping to determine the basis of specificity in signalling molecules. In the area of plant pathology, Jonathan Jones (John Innes Centre, Norwich, UK) addressed the mechanisms used by plants to resist pathogens, in particular those involving the recognition of pathogen-specified molecules. This ‘gene-for-gene’ relationship is based on the capacity for disease resistance genes (R genes) in the plant to recognize pathogens carrying the corresponding avirulence genes (Avr genes) and to promote a defence response. Four classes of R genes have been isolated from a variety of plant species (tomato, Arabidopsis, tobacco, rice and maize) and the functions of the proteins and the associated signalling pathways are currently being examined.
described the benefits that the collection has already given to French and other European scientists and its potential for use in the discovery of new genes that control plant development. The discovery of the involvement of lipochito oligosaccharides in nodule formation in legumes has been one of the most exciting achievements in the area of plant–microbe interactions in recent years. A member of the group who discovered these signalling molecules, Antonius Timmers (CNRS, CastanetTolosan, France) presented new data showing that during early nodule formation, part of the complex dialogue between symbionts displays the ultrastructural and biochemical features associated with a hypersensitive reaction. Finally, Georges Bernier (University of Liège, Belgium) discussed the role of sucrose in the transition to flowering. Metabolism and membrane function
Studies on methionine biosynthesis (Stéphane Ravanel, CNRS, Lyon, France) and the role of iron in higher plants (Jean-François Briat, CNRS, Montpellier, France) are good illustrations of how the integration of different disciplines (biochemistry, cytology, physiology and molecular biology) can aid in the study of regulatory processes in plant metabolism. A brilliant example of this approach by a young scientist was the presentation by E. IsakidisBourget (Orsay), who received the Society’s award for her work on the activation by thioredoxine of the NADP-malate dehydrogenase. Genes encoding ammonium transporters have recently been isolated in plants and characterized in yeast: Nico Von Wiren (University of Tübingen, Germany) described the characterization of these genes and efforts to isolate further members of the family. M. Boutry (University of Louvain, Belgium) has also used expression in yeast to determine the enzymatic properties of members of the plasma membrane H+-ATPase gene family. Studies of the regulation and expression of members of the gene family in Nicotiana plumbaginifolia have shown that each of the eight members is expressed in a different way.
Growth, development and differentiation
Environmental sensing
Jim Haseloff (University of Cambridge, UK) gave an exciting talk, accompanied by a video presentation, of the benefits and potential use of the gene encoding the green fluorescent protein as a reporter. Mireille Rougier (CNRS, Lyon, France) gave an interesting talk on the use of an in vitro fertilization system for maize that has provided new opportunities for studying early cellular and molecular changes occurring in the egg cell upon fertilization. Groups at INRA (Versailles) are currently generating and screening a collection of insertional mutants of Arabidopsis (50 000 insertion lines are expected by 1999). Catherine Bellini (INRA, France)
The role of fatty acid signalling in plant defence was discussed by Edward Farmer (University of Lausanne, Switzerland). He described the identification of a new member of the jasmonate family, dinor-oxo-phytodienoic acid, and raised the possibility that other hexadecanoid-derived signals exist in plants. Using a suspension-cultured plant cell as a model, Georg Felix (Friedrich Miescher Institut, Basel, Switzerland) highlighted the parallels between plant and animal sensing systems. He also showed that, although different chemical stimuli seem to be perceived by different receptors, they appear to induce the same set of primary
120
April 1998, Vol. 3, No. 4
responses, indicating the existence of a common signalling pathway. Dominique de Vienne (CNRS, Gif-sur-Yvette) has investigated the genetic basis of the multiple responses of maize to mild water deprivation using an approach based on quantitative genetic analysis. As with other highly complex traits, a small number of quantitative trait loci (QTLs) can explain a large part of the genetic variability for this trait. Hence, marker-assisted selection based on QTL analysis should be a means of developing varieties more tolerant of water deficit. Genetics and biotechnology
The session on genetics and biotechnology attracted much interest from both the public and private sectors, and revealed the wide range of interplay between fundamental and applied research. There were three particular areas of discussion, starting with the exploitation of natural genetic variation to identify QTLs that can serve as starting points for cloning genes of agronomic interest. Steve Tanksley (Cornell University, Ithaca, USA), a pioneer in this field, gave a good example of achievements in tomato. A second theme was the potential use of retrotransposons as new markers to estimate biodiversity and phylogeny, as described by Marie-Angèle Grandbastien (INRA, Versailles). The final point was the introduction of molecular and biotechnology techniques into the field of genetics. This was illustrated through the examples of seed composition and fruit ripening given by E. Krebbers (Dupont, Wilmington, USA) and Don Grierson (University of Nottingham, UK), respectively. During a general discussion that featured representatives from a range of public and private research and interest groups, it became clear that public concern over the regulation and acceptability of transgenic plants within the European Union remains a barrier to the commercial development of transgenic plant products. However, the recent French agreement for the culture and marketing of maize expressing Bt toxin may well pave the way for further commercialization of the products of plant biotechnology in both France and the rest of Europe. Jean-Claude Pech* and Mondher Bouzayen Ecole Nationale Supérieure Agronomique (ENSAT) and Institut National de la Recherche Agronomique (INRA), Avenue de l’Agrobiopôle, BP 107, Auzeville 31326 Castanet-Tolosan, France
*Author for correspondence (tel +33 5 62 13 65 41; fax +33 5 62 13 65 41; e-mail [email protected]) References 01 Fluhr, R. (1998) Ethylene perception: from twocomponent signal transducers to gene induction, Trends Plant Sci. 3, 141–146
Physiologie végétale Highlights of the third general meeting of the French Society of Plant Physiology* included reports on light-induced signal transduction, use of the green fluorescent protein (the presentation was so enthralling that the speaker was asked to repeat his talk later that same day – an almost unprecedented event at a scientific meeting) and the latest data about the involvement of lipo-chito oligosaccharides in nodule formation in legumes. One of the factors behind the tremendous progress achieved in the plant sciences over the last decade has been the continuing improvement in communication between scientists. This meeting continued the good work, and was an ideal forum for intraand interdisciplinary exchange of ideas, with a strong field of international speakers.
programme, only around 200 of the estimated 20 000 genes had been characterized. Now, more than 30 000 ESTs, corresponding to approximately 12 000 genes, have been placed in the public databases. In parallel with the EST programme, the Arabidopsis genome sequencing project now has the sequence of almost 20% of the Arabidopsis genome. Given the significant conservation of gene order and function between Arabidopsis and other plant species, the information provided by these programmes will undoubtedly continue to
revolutionize plant biology and lead to the improvement of commercially important crops. Hervé Vaucheret [Institut National de la Recherche Agronomique (INRA), Versailles, France] spoke on the recent progress in characterizing the mechanism of transgeneinduced gene silencing in plants. It is now well established that gene silencing occurs at both the transcriptional and post-transcriptional levels. In addition, it has been found that a diffusible factor mediates the systemic transmission of post-transcriptional silencing. The
Gene structure, regulation and function
Michel Delseny (University of Perpignan, France) and G. Murphy (John Innes Centre, Norwich, UK) presented the results of their ground-breaking work on the Arabidopsis expressed sequence tag (EST) and gene sequencing projects. At the outset of the EST
Photos courtesy of J-C. Pech.
*General Meeting of the French Society of Plant Physiology, Toulouse, 1–3 December 1997. Further information on this meeting can be found in a proceedings volume entitled Plant Sciences 1997 available at the Laboratoire du Métabolisme, Institut National de la Recherche Agronomique (INRA), Route de Saint Cyr, F-78026, Versailles Cedex France. Copyright © 1998 Elsevier Science Ltd. All rights reserved. 1360 - 1385/98/$19.00
study of transgene-induced silencing should provide important clues in the understanding of natural plant defence mechanisms that act at the DNA or RNA level to stabilize the genome and protect plants against pathogens. Nicole Chaubet-Gigot (Institut de Biologie Moléculaire des Plantes, Strasbourg, France) described the efforts of her group to elucidate the molecular mechanisms involved in the induction of gene expression at the G1–S transition phase of the plant cell cycle. Through the study of two alternative model genes, those encoding histones and the two subunits of ribonucleotide reductase, the group has developed a model for the sequential induction of genes during the transition. Functional and structural analysis of the histone promoters indicate that transcriptional activation of some histone genes at the G1–S transition is mediated by the modification of prebound factors, April 1998, Vol. 3, No. 4
119
trends in plant science research news probably through protein phosphorylation. Ribonucleotide reductase and histone promoters contain different cis-elements, suggesting that the two model genes are induced by two different regulatory mechanisms. Signal perception and transduction
Knowledge of the ethylene signal-transduction pathway is the most advanced among the plant hormones, and Joe Ecker (University of Pennsylvania, Philadelphia, USA) presented his findings in the area. Progress has come about largely as a result of a simple developmental growth response known as the ‘triple response’. Several classes of mutants altered in ethylene responses have been identified, and a genetic framework has been proposed for the action of the corresponding genes (see also Ref. 1). In addition, G. Neuhaus (University of Freiburg, Germany) described the progress being made in our understanding of the molecular events underlying light-induced signal transduction. One of the elements stressed was the continuous crosstalk between different components in the signalling pathways. The symbiotic interaction between legumes and Rhizobium is a classical example of crosstalk between host plant and bacterium. Michael Schultze [Centre National de la Recherche Scientifique (CNRS), Gif-surYvette, France] described how the molecular dissection of Nod factors is helping to determine the basis of specificity in signalling molecules. In the area of plant pathology, Jonathan Jones (John Innes Centre, Norwich, UK) addressed the mechanisms used by plants to resist pathogens, in particular those involving the recognition of pathogen-specified molecules. This ‘gene-for-gene’ relationship is based on the capacity for disease resistance genes (R genes) in the plant to recognize pathogens carrying the corresponding avirulence genes (Avr genes) and to promote a defence response. Four classes of R genes have been isolated from a variety of plant species (tomato, Arabidopsis, tobacco, rice and maize) and the functions of the proteins and the associated signalling pathways are currently being examined.
described the benefits that the collection has already given to French and other European scientists and its potential for use in the discovery of new genes that control plant development. The discovery of the involvement of lipochito oligosaccharides in nodule formation in legumes has been one of the most exciting achievements in the area of plant–microbe interactions in recent years. A member of the group who discovered these signalling molecules, Antonius Timmers (CNRS, CastanetTolosan, France) presented new data showing that during early nodule formation, part of the complex dialogue between symbionts displays the ultrastructural and biochemical features associated with a hypersensitive reaction. Finally, Georges Bernier (University of Liège, Belgium) discussed the role of sucrose in the transition to flowering. Metabolism and membrane function
Studies on methionine biosynthesis (Stéphane Ravanel, CNRS, Lyon, France) and the role of iron in higher plants (Jean-François Briat, CNRS, Montpellier, France) are good illustrations of how the integration of different disciplines (biochemistry, cytology, physiology and molecular biology) can aid in the study of regulatory processes in plant metabolism. A brilliant example of this approach by a young scientist was the presentation by E. IsakidisBourget (Orsay), who received the Society’s award for her work on the activation by thioredoxine of the NADP-malate dehydrogenase. Genes encoding ammonium transporters have recently been isolated in plants and characterized in yeast: Nico Von Wiren (University of Tübingen, Germany) described the characterization of these genes and efforts to isolate further members of the family. M. Boutry (University of Louvain, Belgium) has also used expression in yeast to determine the enzymatic properties of members of the plasma membrane H+-ATPase gene family. Studies of the regulation and expression of members of the gene family in Nicotiana plumbaginifolia have shown that each of the eight members is expressed in a different way.
Growth, development and differentiation
Environmental sensing
Jim Haseloff (University of Cambridge, UK) gave an exciting talk, accompanied by a video presentation, of the benefits and potential use of the gene encoding the green fluorescent protein as a reporter. Mireille Rougier (CNRS, Lyon, France) gave an interesting talk on the use of an in vitro fertilization system for maize that has provided new opportunities for studying early cellular and molecular changes occurring in the egg cell upon fertilization. Groups at INRA (Versailles) are currently generating and screening a collection of insertional mutants of Arabidopsis (50 000 insertion lines are expected by 1999). Catherine Bellini (INRA, France)
The role of fatty acid signalling in plant defence was discussed by Edward Farmer (University of Lausanne, Switzerland). He described the identification of a new member of the jasmonate family, dinor-oxo-phytodienoic acid, and raised the possibility that other hexadecanoid-derived signals exist in plants. Using a suspension-cultured plant cell as a model, Georg Felix (Friedrich Miescher Institut, Basel, Switzerland) highlighted the parallels between plant and animal sensing systems. He also showed that, although different chemical stimuli seem to be perceived by different receptors, they appear to induce the same set of primary
120
April 1998, Vol. 3, No. 4
responses, indicating the existence of a common signalling pathway. Dominique de Vienne (CNRS, Gif-sur-Yvette) has investigated the genetic basis of the multiple responses of maize to mild water deprivation using an approach based on quantitative genetic analysis. As with other highly complex traits, a small number of quantitative trait loci (QTLs) can explain a large part of the genetic variability for this trait. Hence, marker-assisted selection based on QTL analysis should be a means of developing varieties more tolerant of water deficit. Genetics and biotechnology
The session on genetics and biotechnology attracted much interest from both the public and private sectors, and revealed the wide range of interplay between fundamental and applied research. There were three particular areas of discussion, starting with the exploitation of natural genetic variation to identify QTLs that can serve as starting points for cloning genes of agronomic interest. Steve Tanksley (Cornell University, Ithaca, USA), a pioneer in this field, gave a good example of achievements in tomato. A second theme was the potential use of retrotransposons as new markers to estimate biodiversity and phylogeny, as described by Marie-Angèle Grandbastien (INRA, Versailles). The final point was the introduction of molecular and biotechnology techniques into the field of genetics. This was illustrated through the examples of seed composition and fruit ripening given by E. Krebbers (Dupont, Wilmington, USA) and Don Grierson (University of Nottingham, UK), respectively. During a general discussion that featured representatives from a range of public and private research and interest groups, it became clear that public concern over the regulation and acceptability of transgenic plants within the European Union remains a barrier to the commercial development of transgenic plant products. However, the recent French agreement for the culture and marketing of maize expressing Bt toxin may well pave the way for further commercialization of the products of plant biotechnology in both France and the rest of Europe. Jean-Claude Pech* and Mondher Bouzayen Ecole Nationale Supérieure Agronomique (ENSAT) and Institut National de la Recherche Agronomique (INRA), Avenue de l’Agrobiopôle, BP 107, Auzeville 31326 Castanet-Tolosan, France
*Author for correspondence (tel +33 5 62 13 65 41; fax +33 5 62 13 65 41; e-mail [email protected]) References 01 Fluhr, R. (1998) Ethylene perception: from twocomponent signal transducers to gene induction, Trends Plant Sci. 3, 141–146