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Genetic engineering of superior wood properties and exploiting natural genetic variation found within commercially important trees, such as Eucalyptus spp., promise to increase cellulose biomass production. It is therefore essential to understand the molecular genetics of wood formation. Digital Gene Expression (DGE) profiling is adept in not only assessing the expression level of genes transcriptome-wide, but also in characterising alternative splice forms of transcripts and identifying novel transcripts. Tension wood is a specialised type of wood which functions in the response to mechanical stress in trees and is formed on the upper side of a branch or a bent stem. The characteristics of tension wood differ from normal wood by increased cellulose and xyloglucan content and decreased lignin and xylan content. During tension wood formation, transcriptome-wide changes in the expression of genes involved in secondary cell wall formation underlie changes in cell wall composition. Most notably is an increase in fasciclin-like arabinogalactan protein (FLA) and xyloglucan endotransglucosylase (XTH) and a decrease in lignin biosynthesis gene expression. Differential expression patterns are shown by cellulose synthase (CesA) genes, which have been found to be either up- or down-regulated during tension wood formation. No previous study has profiled gene expression during early as well as late tension wood formation. The aim of this M. Sc study was to identify genes that are differentially expressed during early tension wood induction and late tension wood formation in the immature xylem tissues of Eucalyptus grandis x Eucalyptus urophylla hybrid trees. DGE profiling is a transcriptome-wide expression profiling technique based on ultra-high throughput second generation DNA sequencing technology. The processing, analysis and interpretation of DGE data has not yet been standardised. To address this problem, a case study was performed of DGE data mapping to seven well characterised Eucalyptus grandis CesA (EgCesA) genes. The DGE data processing guidelines developed based on this case study produced EgCesA expression profiles in normal wood that were comparable to the profiles of these genes determined with other technologies. A possible alternative splice variant occurring during tension wood formation was identified for the secondary cell wall gene EgCesA3. However future work is needed for the validation of this observation. Early tension wood induction and late tension wood formation was investigated by sampling differentiating xylem from ramets of a Eucalyptus grandis x Eucalyptus urophylla clone induced to form tension wood for 6 hours, 24 hours, 1 week, 2 weeks and 6 months. Up to 2,654 transcripts were found to be significantly differentially expressed during tension wood formation. FLA transcripts were the highest expressed transcripts and were, along with XTH genes, highly up-regulated in early and late tension wood formation. Genes differentially regulated during early tension wood formation reflected a general stress response and hormone signalling pathways. Late tension wood formation was marked by the differential regulation of secondary cell wall biosynthetic genes, which reflected the chemical composition of tension wood. Two secondary cell wall CesA genes were significantly up-regulated, while genes involved in lignin and xylan biosynthesis were significantly down-regulated. Observations suggest that the eucalypt trees used in this study formed tension wood to stabilise the bent stem, while apical dominance was transferred to new side branches which showed signs of extra secondary growth.
Cellulose is one of the most abundant biopolymers on earth and is an important commodity for industries such as the pulp and paper industry. Cellulose is deposited into the plant cell walls by a complex of membrane bound enzymes known as cellulose synthases. A number of cellulose synthase (CesA) genes, which encode for different cellulose synthase proteins, have been identified from plant species such as Eucalyptus, Populus and Arabidopsis. Mutant and expression profile analysis of the CesA genes indicated that a set of three CesA genes are associated with secondary cell wall formation, while a different set of CesA genes are associated with primary cell wall formation. The aim of this study was to investigate the transcriptional regulation of the different members of the CesA gene family in Eucalyptus. The promoter regions were comparatively analysed with the orthologous regions in Arabidopsis and Populus using bioinformatics tools to identify putative regulatory motifs that playa role in CesA genes regulation. Six Eucalyptus CesA gene promoters were isolated using genome walking. The Eucalyptus promoter regions and the orthologous promoter regions from Populus and Arabidopsis were analysed using TSSP (Transcriptional start site plant promoter prediction) and NNPP (Neural network promoter prediction) software packages. The software packages predicted the transcriptional start sites of the genes and the core regulatory elements such as the TATA-box and initiator elements. The in silico results were compared among species and it was found that the predicted transcriptional start sites and the core elements of the CesA gene promoters showed substantial structural conservation. The promoter regions were used in a comparative in silico analysis with the orthologous promoter regions from Arabidopsis and Populus to identify putative regulatory motifs. This is the first study in which the promoters of the CesA gene family are characterized in Arabidopsis, Populus and Eucalyptus. Three software packages (Weeder, POCO and MotifSampler) were used to analyse the promoter regions and identify over-represented motif sequences. A number of key stem-specific and xylem-specific motifs such as the AC-motif and G-box motif were identified as well as a number of novel motifs. Although all of the predicted motifs identified here will have to be functionally tested, the results of this study provide a good map for directed deletion studies and functional testing of the CesA promoters.
Over the past years, a great deal has been learned about variation in wood prop erties. Genetic control is a major source of variation in most wood properties. Wood is controlled genetically both directly in the developmental or internal pro cesses of wood formation and indirectly by the control of tree form and growth patterns. Emphasis in this book will be on the internal control of wood production by genetics although there will be two chapters dealing with the indirect genetic control of wood, which was covered in detail in the previous book by Zobel and van Buijtenen (1989). The literature on the genetics of wood is very variable, SO'lle quite superficial, on which little reliance can be placed, and some from well-designed and correctly executed research. When suitable, near the end of each chapter, there will be a summary with the authors' interpretation of the most important information in the chapter. The literature on the genetics of wood can be quite controversial. This is to be expected, since both the environment and its interaction with the genotype of the tree can have a major effect on wood properties, especially when trees of similar genotypes are grown under widely divergent conditions. Adding to the confusion, studies frequently have been designed and analyzed quite differently, resulting in conflicting assessments of results.
Our objective was to better understand the regulation of the biosynthesis of the lignified secondary cell walls during wood formation in Eucalyptus, the most planted hardwood tree, and the second whose genome has been sequenced. We functionally characterized three Eucalyptus transcription factors of the R2R3-MYB family and identified EgMYB137 as a new regulator of secondary cell wall deposition. We also showed that the transcriptional activity of EgMYB1, a repressor of lignin biosynthesis was modulated by protein-protein interactions involving a linker histone (EgH1.3). Finally, we set up a homologous transformation system for Eucalyptus using Agrobacterium rhizogenes. The transgenic hairy roots are suitable for high throughput functional characterization of cell wall-related genes. Our findings not only allowed getting new insights into the complexity of the network regulating secondary cell walls but also open new avenues to improve wood quality for industrial applications such as second-generation bioethanol.
Industrial Biotechnology summarizes different aspects of plant biotechnology such as using plants as sustainable resources, phytomedical applications, phytoremedation and genetic engineering of plant systems. These topics are discussed from an academic as well industrial perspective and thus highlight recent developments but also practical aspects of modern biotechnology.
This book presents basic concepts, methodologies and applications of biotechnology for the conservation and propagation of aromatic, medicinal and other economic plants. It caters to the needs and challenges of researchers in plant biology, biotechnology, the medical sciences, pharmaceutical biotechnology and pharmacology areas by providing an accessible and cost-effective practical approach to micro-propagation and conservation strategies for plant species. It also includes illustrations describing a complete documentation of the results and research into particular plant species conducted by the authors over the past 5 years. Plant Biotechnology has been a subject of academic interest for a considerable time. In recent years, it has also become a useful tool in agriculture and medicine, as well as a popular area of biological research. Current economic growth is globally projected in a highly positive manner, but the challenges many countries face with regard to food, feed, malnutrition, infectious diseases, the newly identified life-style diseases, and energy shortages, all of which are worsened by an ever-deteriorating environment, continue to pull the growth digits back. The common thread that connects all of the above challenges is biotechnology, which could provide many answers. Molecular biology and biotechnology have now become an integral part of tissue culture research. The tremendous impact generated by genetic engineering and consequently of transgenics now allows us to manipulate plant genomes at will. There has indeed been a rapid development in this area with major successes in both developed and developing countries. The book introduces several new and exciting areas to researchers who are unfamiliar with plant biotechnology and also serves as a review of ongoing research and future directions for scholars. The book highlights numerous methods for in vitro propagation and utilization of techniques in raising transgenics to help readers reproduce the experiments discussed.
The application of modern molecular biology techniques is providing new insight into wood formation and the seasonal nature of secondary growth in perennial woody plant species. Extensively illustrated, this new book provides a comprehensive and critical overview of current understanding about the biology of wood formation, with a focus on the development, regulation and biochemistry of cambial growth supplemented by additional considerations of the fundamental factors determining forest productivity, wood quality and heartwood formation.
Recent major advances in the field of comparative genomics and cytogenomics of plants, particularly associated with the completion of ambitious genome projects, have uncovered astonishing facets of the architecture and evolutionary history of plant genomes. The aim of this book was to review these recent developments as well as their implications in our understanding of the mechanisms which drive plant diversity. New insights into the evolution of gene functions, gene families and genome size are presented, with particular emphasis on the evolutionary impact of polyploidization and transposable elements. Knowledge on the structure and evolution of plant sex chromosomes, centromeres and microRNAs is reviewed and updated. Taken together, the contributions by internationally recognized experts present a panoramic overview of the structural features and evolutionary dynamics of plant genomes.This volume of Genome Dynamics will provide researchers, teachers and students in the fields of biology and agronomy with a valuable source of current knowledge on plant genomes.