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Wood formation (xylogenesis) is a critical developmental process for all woody land plants. As an initial step to understand the molecular basis for temporal and spatial regulation of xylogenesis and the effect of the expression of individual genes on physical and chemical properties of wood, microarray and realtime RTPCR analyses were performed to monitor gene expression during xylogenesis under various developmental and environmental conditions. The specific objectives established for this study were: Objective 1. Microarray analysis of genes preferentially expressed in differentiating xylem compared to other tissues of loblolly pine (see Chapter II); Objective 2. Microarray analysis of seasonal variation in gene expression for loblolly pines (Pinus taeda L.) from different geographical sources (see Chapter III); Objective 3. Realtime RTPCR analysis of loblolly pine AGP and AGPlike genes (see Chapter IV). Based on the results from this study, candidate genes may be further studied for association with significant traits, used for genetic modification of wood properties, or included in future studies to further examine the molecular mechanisms of wood formation.

Pinus radiata D. Don is an economically important plantation species to New Zealand that is susceptible to the wood quality flaw 'intra-ring checking'. Intra-ring checking is a term used to describe radial fractures that can occur in the earlywood portion of a growth ring, altering the appearance and resilience of the wood, thereby decreasing its economic value. This thesis presents a study that was part of a broad, ongoing collaborative investigation directed at understanding wood quality issues, with the long term goal of enhancement of future radiata pine crops. These investigations are funded by the Wood Quality Initiative Ltd., and involve basic science, field trials and engineering studies related to intra-ring checking. Specifically, the present study was designed to establish the effects of the mineral nutrients boron, calcium and magnesium on wood formation, to determine whether they are associated with intra-ring checking. This research was carried out in three stages. Firstly, the ultra-structural and biochemical properties of wood with intra-ring checking were examined to determine if specific features of the cell wall were associated with the incidence of intra-ring checks. Electron microscopy techniques revealed that the CML/S1 region of the cell wall often showed a decrease in CML lignin staining and S1 striations in wood with intra-ring checks. However, Klason and acetyl bromide assays did not show a change in lignin content. In order to understand how changes in the CML/S1 region of the cell wall may occur, methods were required that would allow for the observation of wood formation in a controlled environment. In the second stage of this study, an organ culture technique was successfully developed to allow for the growth of radiata pine cambial tissue, sandwiched between phloem and xylem, on a defined nutrient medium. This nutrient medium was manipulated, using ion-binding resins, to control the amount of boron, calcium and magnesium available to the growing tissues, to determine if variations in wood formation could be induced. In the final stage of this research, an extensive comparative examination of different techniques that could be used for the observation and measurement of selected wood properties was undertaken, in order to determine the efficacy of the organ cultures to study wood formation in an altered nutrient environment. Wood properties were examined for various stages of xylogenesis, beginning with cell division and expansion, followed by cell wall deposition, and lastly with the onset of lignification in order to define the success of the culture technique. Electron microscopy investigations suggested that in the presence of very little boron the CML/S1 wall showed darker striation deposits, while an increase in calcium availability, resulted in a more defined CML/S1/S2 wall region compared to the controls. Further examination of the cell walls suggested that pectin esterification and possibly lignification could also be increased by limited boron availability. However, in many of the observed and measured parameters of wood properties, a great deal of complex 'between-tree' and 'within-culture' variation was observed. The results show that elucidation of the association between nutrient availability and the incidence of intra-ring checking can not be established from this organ culture study. In a concurrent study, the preliminary investigation of arabinogalactan-proteins (AGPs) in radiata pine was undertaken. Radiata pine AGPs were positioned in the compound middle lamella of xylem cells, suggesting potential roles in cell-cell adhesion or cell-cell signalling. For the first time, radiata pine AGPs were isolated and characterized in terms of their protein and carbohydrate composition, both of which yielded features typical of AGPs in other plant species. Unique to radiata pine AGPs was the presence of a large proportion of 5-linked arabinose. While the precise function(s) of AGPs are unknown, the results obtained in this research have established a basis for further investigation into the potential for their involvement in wood formation. Overall, new tools have been established to facilitate future research on radiata pine, a commercially important species, and novel results have been obtained concerning the mechanisms of wood formation therein.

Pinus radiata D. Don is an economically important plantation species to New Zealand that is susceptible to the wood quality flaw 'intra-ring checking'. Intra-ring checking is a term used to describe radial fractures that can occur in the earlywood portion of a growth ring, altering the appearance and resilience of the wood, thereby decreasing its economic value. This thesis presents a study that was part of a broad, ongoing collaborative investigation directed at understanding wood quality issues, with the long term goal of enhancement of future radiata pine crops. These investigations are funded by the Wood Quality Initiative Ltd., and involve basic science, field trials and engineering studies related to intra-ring checking. Specifically, the present study was designed to establish the effects of the mineral nutrients boron, calcium and magnesium on wood formation, to determine whether they are associated with intra-ring checking. This research was carried out in three stages. Firstly, the ultra-structural and biochemical properties of wood with intra-ring checking were examined to determine if specific features of the cell wall were associated with the incidence of intra-ring checks. Electron microscopy techniques revealed that the CML/S1 region of the cell wall often showed a decrease in CML lignin staining and S1 striations in wood with intra-ring checks. However, Klason and acetyl bromide assays did not show a change in lignin content. In order to understand how changes in the CML/S1 region of the cell wall may occur, methods were required that would allow for the observation of wood formation in a controlled environment. In the second stage of this study, an organ culture technique was successfully developed to allow for the growth of radiata pine cambial tissue, sandwiched between phloem and xylem, on a defined nutrient medium. This nutrient medium was manipulated, using ion-binding resins, to control the amount of boron, calcium and magnesium available to the growing tissues, to determine if variations in wood formation could be induced. In the final stage of this research, an extensive comparative examination of different techniques that could be used for the observation and measurement of selected wood properties was undertaken, in order to determine the efficacy of the organ cultures to study wood formation in an altered nutrient environment. Wood properties were examined for various stages of xylogenesis, beginning with cell division and expansion, followed by cell wall deposition, and lastly with the onset of lignification in order to define the success of the culture technique. Electron microscopy investigations suggested that in the presence of very little boron the CML/S1 wall showed darker striation deposits, while an increase in calcium availability, resulted in a more defined CML/S1/S2 wall region compared to the controls. Further examination of the cell walls suggested that pectin esterification and possibly lignification could also be increased by limited boron availability. However, in many of the observed and measured parameters of wood properties, a great deal of complex 'between-tree' and 'within-culture' variation was observed. The results show that elucidation of the association between nutrient availability and the incidence of intra-ring checking can not be established from this organ culture study. In a concurrent study, the preliminary investigation of arabinogalactan-proteins (AGPs) in radiata pine was undertaken. Radiata pine AGPs were positioned in the compound middle lamella of xylem cells, suggesting potential roles in cell-cell adhesion or cell-cell signalling. For the first time, radiata pine AGPs were isolated and characterized in terms of their protein and carbohydrate composition, both of which yielded features typical of AGPs in other plant species. Unique to radiata pine AGPs was the presence of a large proportion of 5-linked arabinose. While the precise function(s) of AGPs are unknown, the results obtained in this research have established a basis for further investigation into the potential for their involvement in wood formation. Overall, new tools have been established to facilitate future research on radiata pine, a commercially important species, and novel results have been obtained concerning the mechanisms of wood formation therein.

Les propriétés du bois de pin maritime varient aux niveaux chimique, anatomique et mécanique. Six types de bois peuvent être trouvés au sein d’un même arbre : bois précoce, bois tardif, bois de couronne, bois de base, bois de compression et bois opposé. Au cours de cette thèse, nous avons testé l’hypothèse selon laquelle la variabilité phénotypique des propriétés de bois, serait liée à l’expression différentielle des protéines lors de la xylogénèse. Par une approche protéomique basée sur l’électrophorèse bidimensionnelle et la spectrométrie de masse en tandem (LC ESI MS/MS), nous avons identifié 165 protéines différentiellement exprimées le long d’un gradient d’âge cambial (bois juvénile vs. bois mature) ainsi que 93 protéines différentiellement exprimées au cours de la saison de végétation (bois de printemps vs. bois d’été) chez le pin maritime. Une analyse chimique complémentaire des échantillons a été réalisée par pyrolyse analytique. Nos résultats montrent que le xylème secondaire formé en début de saison ainsi que celui qui est initié par un cambium jeune présentent une sur-expression de protéines participant à la division cellulaire. Dans le xylème issu d’un cambium âgé ou formé à la fin de l’été nous avons mis en évidence des protéines impliquées dans la défense cellulaire (dont le rôle serait de retarder la mort cellulaire programmée), ainsi que des protéines impliqués dans la biosynthèse des éléments constitutifs de la paroi. Cette étude contribue à renforcer nos connaissances sur les acteurs moléculaires intervenant lors de la xylogénèse. Elle ouvre par ailleurs des pistes de recherche sur la détection de gènes impliqués dans le contrôle génétique des propriétés du bois dans un objectif de sélection assisté par marqueurs. / Wood properties in maritime pine are highly variable at chemical, anatomical and mechanical levels. Six types of wood can be found in a single tree, early wood, late wood, crown wood, base wood, compression wood and opposite wood. In this thesis report, we tested the hypothesis that the observed variability at the phenotypic level, can be bound to the differential expression of proteins during the process of wood formation. We use the tools of proteomics, Bidimensional electrophoresis and LC ESI MS/MS for the discovery of 165 proteins differentially expressed in a cambial age gradient, (from base wood to crown wood), an 93 overexpressed proteins in a seasonal gradient (from early wood collected at the beginning of the growing season, to late wood, collected at summer) Complementary, chemical characterization of the samples was performed using analitycal pyrolisis. Our results showed that the secondary xylem formed at the beginning of the growing season, and the xylem formed by a young cambium, present a overexpression of proteins participating in the intense cell division, characteristical of those tissues, e.g. Biogenesis of cytoskeleton and hemicelluloses, RNA transcription, synthesis, folding and modification of proteins. In the xylem formed at the base of the trunk and at the end of the growing season we have found an over-expression of proteins from cell defense (they role will be to delay programmed cell death) and cell wall formation related proteins e.g. lignin biosynthesis. This study contributes to reinforce our knowledge over the molecular actors involved in the xylogenesis process. It opens, in another hand , research guides for the detection of genes involved in the genetic control of wood properties towards an objecive of marker assisted selection.

O gênero Eucalyptus é a fonte principal de madeira para a indústria de papel e celulose de países tropicais e subtropicais e tem sido extensivamente estudado. Apesar de sua importância econômica, muito pouco é conhecido sobre o controle genético da formação da madeira (xilogênese) no eucalipto. Diferentes propriedades da madeira são observadas durante o desenvolvimento das árvores e a madeira é classificada como madeira juvenil e adulta. A madeira juvenil comparada à adulta apresenta células com paredes delgadas, alta concentração de lignina e baixa densidade; características indesejáveis para a indústria florestal. A identificação de proteínas e genes que regulam os processos genéticos de formação da madeira juvenil e adulta é, portanto, alvo potencial para estudos relacionados a modificações específicas visando melhorar a qualidade da madeira. O objetivo deste trabalho foi identificar as proteínas da região cambial de árvores de Eucalyptus grandis envolvidas no processo de formação da madeira adulta. A proteína total foi extraída de árvores com 22 anos e submetida à eletroforese bidimensional. Os spots foram isolados de cada uma das repetições do gel e após digestão tríptica, submetidos ao sequenciamento por cromatografia líquida associada ao espectrômetro de massas Q-TOF Ultima API (Waters, UK). Os espectros foram analisados pelo programa MASCOT MS/MS Ion Search, utilizando o banco de dados MSDB. Um total de 82 proteínas foram identificadas e classificadas em seis categorias funcionais: metabolismo e energia (36%), processos celulares (11%), transporte (2%), estrutura e organização da estrutura (11%), vias de informação (30%) e sem função definida (10%). Muitas das proteínas identificadas participam dos mecanismos de controle da biossíntese da parede celular e, conseqüentemente, da formação da madeira. Os dados gerados irão facilitar uma futura comparação e seleção de proteínas diferencialmente expressas em árvores juvenis e adultas durante xilogênese. / The Eucalyptus genus is the main source of hardwood for the pulp and paper industry in tropical and subtropical countries and is being extensively studied. Despite its economical importance, very little is known about the genetic control of wood formation (xylogenesis) in eucalypts. Different wood properties are observed during tree development and the wood is classified as juvenile and mature. The juvenile wood is characterized by cells with large lumen and thinner walls, lower density, higher lignin content and poor quality for pulp production, when compared to mature wood. The identification of proteins and genes that regulate the process in both mature and juvenile wood formation is, therefore, a potential target for studies related to specific modifications to alter wood quality. The aim of this work was to identify proteins which participate in the process involved in mature wood formation by isolating proteins from the cambial region of Eucalyptus grandis. The total protein was extracted from 22 year-old trees and two-dimensional gel electrophoresis was carried out. Proteins were excised from the gels and after tryptic digestion, MS analysis was conducted by on line chromatography using a Cap-LC coupled to a Q-TOF Ultima API mass spectrometer (Waters, UK). The spectra were processed using MASCOT MS/MS Ion Search (www.matrixscience.com), and the sequences searched against MSDB database. A total of 82 proteins were identified and classified into six main functional categories: metabolism and energy (36%), cellular processes (11%), transport (2%), structure and structural organization (11%), information pathways (30%), non defined function (10%). Many of the identified proteins play a role in the mechanisms involved in the control of cell wall biosynthesis, and consequently in wood formation. The generated data will facilitate a further comparison and selection of proteins differentially expressed in mature and juvenile trees during xylogenesis.

O gênero Eucalyptus é a fonte principal de madeira para a indústria de papel e celulose de países tropicais e subtropicais e tem sido extensivamente estudado. Apesar de sua importância econômica, muito pouco é conhecido sobre o controle genético da formação da madeira (xilogênese) no eucalipto. Diferentes propriedades da madeira são observadas durante o desenvolvimento das árvores e a madeira é classificada como madeira juvenil e adulta. A madeira juvenil comparada à adulta apresenta células com paredes delgadas, alta concentração de lignina e baixa densidade; características indesejáveis para a indústria florestal. A identificação de proteínas e genes que regulam os processos genéticos de formação da madeira juvenil e adulta é, portanto, alvo potencial para estudos relacionados a modificações específicas visando melhorar a qualidade da madeira. O objetivo deste trabalho foi identificar as proteínas da região cambial de árvores de Eucalyptus grandis envolvidas no processo de formação da madeira adulta. A proteína total foi extraída de árvores com 22 anos e submetida à eletroforese bidimensional. Os spots foram isolados de cada uma das repetições do gel e após digestão tríptica, submetidos ao sequenciamento por cromatografia líquida associada ao espectrômetro de massas Q-TOF Ultima API (Waters, UK). Os espectros foram analisados pelo programa MASCOT MS/MS Ion Search, utilizando o banco de dados MSDB. Um total de 82 proteínas foram identificadas e classificadas em seis categorias funcionais: metabolismo e energia (36%), processos celulares (11%), transporte (2%), estrutura e organização da estrutura (11%), vias de informação (30%) e sem função definida (10%). Muitas das proteínas identificadas participam dos mecanismos de controle da biossíntese da parede celular e, conseqüentemente, da formação da madeira. Os dados gerados irão facilitar uma futura comparação e seleção de proteínas diferencialmente expressas em árvores juvenis e adultas durante xilogênese. / The Eucalyptus genus is the main source of hardwood for the pulp and paper industry in tropical and subtropical countries and is being extensively studied. Despite its economical importance, very little is known about the genetic control of wood formation (xylogenesis) in eucalypts. Different wood properties are observed during tree development and the wood is classified as juvenile and mature. The juvenile wood is characterized by cells with large lumen and thinner walls, lower density, higher lignin content and poor quality for pulp production, when compared to mature wood. The identification of proteins and genes that regulate the process in both mature and juvenile wood formation is, therefore, a potential target for studies related to specific modifications to alter wood quality. The aim of this work was to identify proteins which participate in the process involved in mature wood formation by isolating proteins from the cambial region of Eucalyptus grandis. The total protein was extracted from 22 year-old trees and two-dimensional gel electrophoresis was carried out. Proteins were excised from the gels and after tryptic digestion, MS analysis was conducted by on line chromatography using a Cap-LC coupled to a Q-TOF Ultima API mass spectrometer (Waters, UK). The spectra were processed using MASCOT MS/MS Ion Search (www.matrixscience.com), and the sequences searched against MSDB database. A total of 82 proteins were identified and classified into six main functional categories: metabolism and energy (36%), cellular processes (11%), transport (2%), structure and structural organization (11%), information pathways (30%), non defined function (10%). Many of the identified proteins play a role in the mechanisms involved in the control of cell wall biosynthesis, and consequently in wood formation. The generated data will facilitate a further comparison and selection of proteins differentially expressed in mature and juvenile trees during xylogenesis.

The genetic manipulation of perennial woody tree species presents a range of additional challenges compared to that of annual weedy crop species. These include long generation times and reproductive cycle, the heterogeneity of plants under investigation and, when investigating xylogenesis, a number of physical and biochemical limitations to microscopic and molecular experimentation. Efforts have been made to understand molecular aspects of xylogenesis and have involved functional gene testing using transgenic approaches. These methods involve the production of plantlets from a variety of plant tissues using in vitro full plant regeneration techniques. Although these systems are effective, the time taken from transformation event, to plant establishment and growth, then finally to secondary wood production can take up to several years and requires high labor and technical inputs. (For complete abstract open document)

Du fait de sa croissance exceptionnelle combinée aux propriétés supérieures de son bois, l'Eucalyptus est devenu le feuillu le plus planté au monde et s'est imposé comme source de biomasse pour la production de papier et de biocarburants de seconde génération. Le bois est composé de parois secondaires lignifiées et sa formation est finement régulée par un réseau complexe, et globalement mal connu, de facteurs de transcription (FT). Les parois secondaires sont composées de 80% de polysaccharides, ciblés pour la plupart des bioproduits à haute valeur ajoutée, tandis que la lignine (20%) est responsable de la récalcitrance de la biomasse à la dégradation enzymatique mais augmente le potentiel énergétique du bois par combustion. Malgré son adaptabilité remarquable à différents sols et climats, la croissance de l'Eucalyptus varie fortement suivant ces facteurs. L'Eucalyptus est largement planté sur des sols lessivés dans les régions tropicales et subtropicales où les plantations industrielles font face à des épisodes de sécheresse de plus en plus fréquents, en combinaison avec des forts manques de nutriments, nécessitant de gros apports en fertilisants. Dans les région tempérées telles que l'Europe du Nord, la principale limitation à l'implantation de cet arbre dépourvu d'endodormance, est l'exposition au froid. Ces contraintes abiotiques sont aggravées par le changement climatique et leur impact sur la formation du bois et sa qualité restent peu documentés. Quelques données suggèrent que ces stress affectent le dépôt de la paroi secondaire ainsi que la structure du xylème. Cependant, ces résultats sont très hétérogènes entre différentes espèces et principalement focalisés sur des tissus différents du bois. La sélection de clones adaptés et le développement de pratiques culturales plus viables, sont essentiels pour améliorer la productivité et la qualité du bois, ce qui requiert une meilleure compréhension de la réponse des arbres au froid et au manque d'eau en interaction avec la nutrition. Dans le but de décrypter les régulations induites par le froid dans la différenciation du xylème, nous avons effectué une approche ciblée sur des Eucalyptus acclimatés au froid. Des analyses de biochimie, d'histochimie et de transcriptomique, ont révélé que le froid déclenche un dépôt de paroi secondaire précoce dans les cellules du xylème en développement, caractérisé par un fort dépôt de lignine. En parallèle, pour caractériser l'effet du manque d'eau combiné à différents régimes nutritifs, sur la formation et la qualité du bois, nous avons tiré profit d'un dispositif expérimental mis en place au champ avec un clone commercial d'Eucalyptus, soumis à une exclusion de pluie combinée à une fertilisation au potassium. Nous avons combiné des analyses globales du transcriptome et du métabolome, avec l'analyse des propriétés structurales et biochimiques du bois. L'approche intégrative de ces jeux de données a révélé que la fertilisation au potassium induit une répression de la biosynthèse de la paroi secondaire ainsi qu'une régulation de l'activité cambiale et la modification dans les propriétés du bois, avec une forte interaction avec l'exclusion d'eau. Ces deux approches ont permis l'identification de différents FT non caractérisés qui constituent des candidats prometteurs dans le contrôle de l'activité cambiale et du dépôt de paroi secondaire chez un ligneux. Leur caractérisation fonctionnelle chez le peuplier et l'Eucalyptus a révélé un nouveau régulateur clé de la biosynthèse de paroi secondaire, et plusieurs facteurs MYB potentiellement impliqués dans la balance entre formation de la paroi secondaire et croissance. / Due to its outstanding growth combined to superior wood properties, Eucalyptus genus has become the most planted hardwood on earth and emerged as the most appealing sources of renewable biomass feedstock for paper and second-generation biofuels. Wood is composed of lignified secondary cell walls (SCWs) and its formation is tightly regulated by a complex, partially unknown, transcription factors (TFs) network. SCWs are composed by 80% of polysaccharides targeted for most of value-added bioproducts, whereas lignin (20%) is responsible for biomass recalcitrance to enzymatic degradation but increase wood energetic potential for combustion. Despite its remarkable adaptability to various soils and climate environment Eucalyptus growth varies strongly according to these factors. Eucalyptus is extensively grown in highly weathered soils in tropical and subtropical regions where plantations are facing more frequent drought episodes in combination to nutrient starvation, requiring high amounts of expensive fertilizers. In temperate regions such as North of Europe, the main limitation for the expansion of this non-dormant tree is cold exposure, which reduces dramatically its growth. The effects of these stresses are emphasized in the actual context of climate change which induces sharp contrasting periods, and their impacts on wood formation and quality remain unknown. Scarce data from literature suggest that these stresses affect secondary cell wall (SCW) deposition as well as xylem cell patterning. However these results are highly heterogeneous among different species and mainly focused on non-woody tissues. The selection of adapted clones and the development of more sustainable cultural practices are crucial to improve wood productivity and quality, which require a better understanding of tree response to cold and water stress in interaction with nutrition. In order to unravel the regulation of xylem differentiation by low temperature, we performed a targeted approach on cold-acclimated Eucalyptus trees. By biochemical, histochemical and transcriptomic analyses, we revealed that low temperature trigger a precocious SCW deposition in developing xylem cells, characterized by a strong lignin deposition. In parallel, we aimed to characterize the effect of water stress combined to different mineral nutrition regimes, on wood formation and quality. To this end, we took advantage of an experimental design set up on field with a highly productive Eucalyptus commercial clone submitted to both rainfall exclusion combined to potassium fertilization. We combined large scale analyses of transcriptome and metabolome, with wood structural and biochemical properties analyses. The integrative approach with these datasets revealed that potassium fertilization induces a repression of SCW biosynthesis, together with regulation of cambial activity and modifications in wood properties, with a strong interaction with water exclusion. Both approaches allowed to point out several uncharacterized yet TFs which are highly promising candidates in the control of cambial activity and SCW deposition in a woody perennial. Characterization of their function in poplar and Eucalyptus revealed a new key regulator of SCW biosynthesis in wood, and several MYB TFs potentially involved in the trade-off between SCW biosynthesis and growth.

L'Eucalyptus, feuillu le plus planté dans le monde, est fortement exposé au froid en raison de l'absence de dormance. Les gènes DREB sont connus comme étant les principaux régulateurs de la réponse aux stress abiotiques. Un nombre élevé de gènes DREB1/CBF (C-Repeat Factor) a été identifié chez Eucalyptus grandis. Le but de l'étude est de mieux comprendre le rôle de la voie DREB chez Eucalyptus pour le contrôle de la tolérance au stress, du développement et de la formation du bois. La présente étude a permis une annotation des gènes CBF et DREB2 dans le cadre d'un projet de sequençage partiel du génome d'E. gunnii. Une analyse complète de l'expression des genes par qRT-PCR a été réalisée sur les différents organes des deux espèces d'Eucalyptus après les traitements au stress. L'existence d'une copie de CBF supplémentaire dans le génome E. gunnii par rapport à E. grandis suggère que ce groupe est encore en évolution contrairement au groupe DREB2. Un nombre élevé de transcrits CBF chez E. gunnii, tolérant au froid, et forte une vitesse d'induction ce ces facteurs chez E. grandis, à croissance rapide, suggère que les facteurs CBF sont impliqués à la fois dans la protection au stress et la limitation de croissance. Des facteurs de transcription des familles MYB, NAC, KNOX et AP2/ERF impliqués dans le contrôle de la croissance et de la formation de la paroi cellulaire ont été identifiés comme étant des gènes putatifs cibles de CBF. Ces résultats sont en accord avec le phénotype modifié de surexpresseurs CBF. Les deux approches suggèrent un rôle central de la voie de DREB dans le compromis entre la croissance et la résistance au stress chez cette espèce ligneuse. / Eucalyptus, the most widely planted hardwood in the world, is highly exposed to the cold due to the lack of dormancy. DREB (Drought Responsive Element Binding) genes are known as master regulators of abiotic stress response. A high number of the DREB1/CBF (C-Repeat Factor) genes has been annotated in Eucalyptus grandis. The aim of the study was to better understand the role of DREB pathway in Eucalyptus for the control of stress tolerance, development and wood formation. The present study provides an annotation of the CBF and DREB2 genes from a partial draft of the E. gunnii genome sequence. A comprehensive transcriptional analysis through high-throughput qRT-PCR was carried out on different organs from the two Eucalyptus species after stress treatments. An additional CBF copy in the E. gunnii genome compared to E. grandis suggests that this group is still evolving unlike the DREB2 group. The higher CBF transcript amounts in the cold tolerant E. gunnii together with higher induction rates in the fast growing E. grandis suggest that CBF factors promote both stress protection and growth limitation. In addition, transcription factors from MYB, NAC, KNOX and AP2/ERF families involved in the control of growth and cell wall formation have been identified as putative CBF target genes. These results are in agreement with the modified phenotype of CBF overexpressors. Both approaches suggest a central role of DREB pathway in the trade-off between growth and stress resistance in this woody species.