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| Author(s): |
Danielle Gregório Gomes Caldas
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2007-09-13 |
| Advisor: | Carlos Alberto Labate |
| Abstract | |
Currently, Brazil is the largest producer of pulp and paper using short fiber from Eucalyptus, with a well developed and established forest sector, that generates many jobs and income for the country. The wood for the Brazilian industries is taken exclusively from planted forests, where 1.27 million hectares correspond to Eucalyptus plantations. During many years, genetic improvement programs have explored the high growth rates, biomass production and adaptability of this genus to reach high productivity, approximately 45 m3/ha/year. However, national and international demand for Eucalyptus wood is increasing and to ensure the competitiveness of this sector, it is necessary to search for a better quality wood, which allows more efficient pulp and paper production. The knowledge of the processes that lead to the wood formation, a tissue that differentiates from the vascular cambium, will certainly contribute to reach this goal. Trees normally acquire the characteristics desired by industry when adult, but Eucalyptus is cut when it is still in juvenile phase of development. Therefore, the objective of this work was to produce a transcriptional profile of the cambial region of Eucalyptus grandis in the juvenile phase of development and, with this information, compare the expression of some genes involved in wood formation in the cambial region of juvenile and mature trees. A SAGE library was produced generating 22660 tags, of which 2942 represented unique tags with two or more copies. Of these, 874 could be associated with a probable function and were classified in functional categories. SAGE allowed the access to genes with low expression levels, the identification of potential anti-sense and alternative transcripts, and disclosed the presence of many sequences not yet characterized. The data were also organized to demonstrate the main pathways involved at each differentiation stage during xylogenesis. The genes for the major enzymes involved in cell wall expansion, secondary cell wall deposition and lignification were found and their expression levels indicated the preferential use of alternative branches in some of the metabolic pathways used by the cambial cells of E. grandis to produce juvenile wood. The expression data obtained with SAGE was validated through Real Time RT-PCR. Twenty five genes involved with cell wall expansion, cellulose and hemicelulose biosynthesis, secondary wall deposition, lignification and metabolism were selected to compare the cambial regions of juvenile and mature E. grandis trees using Real Time RT-PCR. The results showed the existence of a differential expression pattern between the ages, were 15 genes were more expressed in the juvenile trees and 6 genes were more expressed in the mature trees. The quantitative characterization of the genes expressed in the cambial region of E. grandis constitutes, therefore, a great information source that might drive the studies to different approaches related to the complex process of wood biosynthesis. (AU) | |