| Differences in physical and chemical properties between juvenile and mature wood are a major source of wood variation within individual trees. This variation results in non-uniform wood products, a quality problem that can be approached through genetic improvement. Studies on the heritability of juvenile and mature wood formation have provided crucial information for designing and deploying breeding projects, but little information regarding the molecular mechanism of juvenile and mature wood development.; This research approached juvenile and mature wood formation from a molecular biology perspective. A hypothesis that the differences of physical and chemical properties were resulted from differential gene expression patterns were raised and test by combining Subtractive Suppression hybridization PCR (SSH-PCR) and reverse Northern dot-blot analysis. The results showed that most differentially expressed genes analyzed have functions correspond well with the differences in physical and chemical properties. Stress-related genes such as low molecular weight heat shock proteins, galactinol synthase, xyloglucan β-1,4 endo transglycosylase, and laccase were among the most highly differentially expressed. Based on these results, a hypothesis that juvenile wood formation could be a combinatorial effect of stresses were raised.; To test the hypothesis, global gene expression patterns between juvenile and mature wood formation and stresses, including heat, drought and bending, were compared. A method of applying local regression for microarray background correction and data normalization was developed and shown to be effective in correcting data from arrays with high background noise. Variation from technical sources and environmental effects was also surveyed.; By profiling gene expression patterns of 3072 genes in juvenile and mature wood, and in response to heat, drought and bending stresses, 359 responsive genes were identified. Principal components analysis and hierarchical clustering revealed seven major functional clusters. Comparison of the global expression patterns showed a high correlation between heat and drought stresses; a negative correlation between juvenile:mature wood transition and both heat and drought stresses; and little resemblance between expression patterns in response to bending and those related to juvenile:mature transition and stresses. The results suggest that juvenile wood formation is not a result of stress, but is instead under a unique genetic control. |
