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UBC Theses and Dissertations

Role of two Populus trichocarpa endo-beta-1,4-glucanases and their Arabidopsis orthologs in plant cell wall development Hrynkiewicz-Moczulski, Magdalena


Plant cell walls are imperative to the normal growth and development of plants as they serve many functions, including protecting the protoplast and providing rigidity to the stem. In this study two poplar and Arabidopsis endoglucanases, which have been hypothesized to play a role in secondary cell wall development, were examined. The Class B endoglucanases, PtGH9B5 and AtGH9B5, are secreted enzymes that have a predicted GPI anchor, while the Class C endoglucanases, PtGH9C2 and AtGH9C2, are also predicted to be secreted but contain a carbohydrate-binding module (CBM). The poplar endoglucanases were up-regulated in Arabidopsis using a 35S promoter as well as the Arabidopsis CesA8 promoter, respectively. Additionally, Arabidopsis t-DNA insertion lines of each Arabidopsis gene were analyzed, and an RNAi construct was created to down-regulate AtGH9C2 in Arabidopsis. All of the transgenic plant lines were examined for changes in cell morphology and patterning, growth and development, cell wall crystallinity, microfibril angle, and proportion of cell wall carbohydrates. Mis-regulation of PtGH9B5/AtGH9B5 resulted in changes in glucose and xylose content, suggesting that this endoglucanase may be involved in regulating the amount of cellulose and/or xylans in the developing secondary cell wall. Furthermore, mis-regulation of PtGH9C2/AtGH9C2 resulted in a change in crystallinity, which was inversely correlated with a change in plant height and rosette diameter. This suggests that this endoglucanase may be involved in modifying cell wall crystallinity at the time of primary growth cessation and/or early secondary cell wall development. Together, these results support the role of these endoglucanases in secondary cell wall development, though their exact enzymatic function remains to be discovered.

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