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Evaluating the role of the raffinose family of oligosaccharides in hybrid poplar

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dc.contributor.author Unda, Faride
dc.date.accessioned 2012-10-10T18:59:16Z
dc.date.available 2012-10-10T18:59:16Z
dc.date.copyright 2012 en
dc.date.issued 2012-10-10
dc.identifier.uri http://hdl.handle.net/2429/43360
dc.description.abstract The raffinose family of oligosaccharides (RFO) function as transport carbohydrates in the phloem, storage compounds in sink tissues, and as putative metabolic agents that combat plant stresses. Research on the RFO pathway has focused on seed biology and plants that transport raffinose as their primary photoassimilate. In contrast, few studies have explored this pathway in woody species. As such, this thesis investigated the fundamental function of the RFO enzymes in hybrid poplar, with emphasis on galactinol synthase (GolS), an enzyme key to the pathway. Phylogenetic comparisons of Populus Go1S with other known GolS suggest a putative role for these enzymes in stress response. Protein analysis of two heterologously expressed isoforms demonstrated that they are true Go1S; with Pa×gGolSI possessing a broader pH and temperature range than Pa×gGolSII. Expression patterns also revealed that the Pa×gGolSII transcript abundance varied seasonally. Together, the results suggest that Pa×gGolSI may be involved in basic metabolic activities, while Pa×gGolSII is likely involved in seasonal mobilization of carbohydrates. To further elucidate the in-planta Go1S function, transgenic trees with mis-regulated GolS were generated. Two AtGolS3 over-expression (OE) transgenic lines showed effects on growth, while other lines appeared normal and possessed marginally modified cell wall characteristics. The extreme over-expressers were severely stunted and had cell wall traits characteristic of tension wood. AtGolS3-OE lines showed reduction in the microfibril angle, increase in cell wall crystallinity and possessed higher cellulose, and lower mannose and lignin contents. Interestingly, although galactinol and raffinose contents increased dramatically, they were not more tolerant to abiotic stress under the conditions tested. These results suggest that the over-expression of GolS and its product galactinol may serve as a molecular signal that initiates different metabolic changes for combating stress, culminating in the formation of tension wood. Additionally, over expression of raffinose synthase (RFS) resulted in increased biomass and total cellulose content. However, it does not appear to have a similar signalling role. Collectively, this research opens new insight about functions of the RFO in poplar, with the participation of GolS in stress signalling and consequent tension wood formation, and the importance of RFS to carbon allocation and growth. en
dc.language.iso eng en
dc.publisher University of British Columbia en
dc.title Evaluating the role of the raffinose family of oligosaccharides in hybrid poplar en
dc.type Electronic Thesis or Dissertation en
dc.degree.name Doctor of Philosophy - PhD en
dc.degree.discipline Forestry en
dc.degree.grantor University of British Columbia en
dc.date.graduation 2012-11 en
dc.degree.campus UBCV en
dc.description.scholarlevel Graduate en

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