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.
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Claims 20
Claim · model-written summary
Phylogenetic comparisons suggest Populus Go1S may have a stress-response role.
PopulusNot reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Phylogenetic comparisons of Populus Go1S with other known GolS suggest a putative role for these enzymes in stress response.”
t0“hybrid poplar”
Claim · model-written summary
Protein analysis verified that the two expressed isoforms are Go1S.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Protein analysis of two heterologously expressed isoforms demonstrated that they are true Go1S”
t0“hybrid poplar”
Claim · model-written summary
Pa×gGolSI had a broader pH and temperature range than Pa×gGolSII.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Pa×gGolSI possessing a broader pH and temperature range than Pa×gGolSII”
t0“hybrid poplar”
Claim · model-written summary
Pa×gGolSII transcript abundance varied seasonally.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the Pa×gGolSII transcript abundance varied seasonally”
t0“hybrid poplar”
Claim · model-written summary
The authors infer Pa×gGolSI may support basic metabolism.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Pa×gGolSI may be involved in basic metabolic activities”
t0“hybrid poplar”
Claim · model-written summary
The authors infer Pa×gGolSII likely participates in seasonal carbohydrate mobilization.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Pa×gGolSII is likely involved in seasonal mobilization of carbohydrates”
t0“hybrid poplar”
Claim · model-written summary
Two AtGolS3 over-expression lines showed growth effects.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Two AtGolS3 over-expression (OE) transgenic lines showed effects on growth, while other lines appeared normal”
t0“hybrid poplar”
Claim · model-written summary
Other over-expression lines had marginal cell-wall changes.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“other lines appeared normal and possessed marginally modified cell wall characteristics”
t0“hybrid poplar”
Claim · model-written summary
Extreme over-expressers were severely stunted.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The extreme over-expressers were severely stunted”
t0“hybrid poplar”
Claim · model-written summary
Extreme over-expressers developed tension-wood traits.
- Outcome
- cell wall traits characteristic of tension woode0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“had cell wall traits characteristic of tension wood”
t0“hybrid poplar”
Claim · model-written summary
AtGolS3-OE lines had reduced microfibril angle.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“AtGolS3-OE lines showed reduction in the microfibril angle”
t0“hybrid poplar”
Claim · model-written summary
AtGolS3-OE lines had increased cell-wall crystallinity.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“AtGolS3-OE lines showed reduction in the microfibril angle, increase in cell wall crystallinity”
t0“hybrid poplar”
Claim · model-written summary
AtGolS3-OE lines had higher cellulose content.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“AtGolS3-OE lines showed reduction in the microfibril angle, increase in cell wall crystallinity and possessed higher cellulose”
t0“hybrid poplar”
Claim · model-written summary
AtGolS3-OE lines had lower mannose content.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“AtGolS3-OE lines showed reduction in the microfibril angle, increase in cell wall crystallinity and possessed higher cellulose, and lower mannose”
t0“hybrid poplar”
Claim · model-written summary
AtGolS3-OE lines had lower lignin content.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“AtGolS3-OE lines showed reduction in the microfibril angle, increase in cell wall crystallinity and possessed higher cellulose, and lower mannose and lignin contents”
t0“hybrid poplar”
Claim · model-written summary
Galactinol and raffinose contents increased dramatically in the transgenic lines.
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“although galactinol and raffinose contents increased dramatically”
t0“hybrid poplar”
Claim · model-written summary
The lines were not more tolerant to abiotic stress under the tested conditions.
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“they were not more tolerant to abiotic stress under the conditions tested”
t0“hybrid poplar”
Claim · model-written summary
The authors propose that GolS over-expression and galactinol signal tension-wood formation.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“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”
t0“hybrid poplar”
Claim · model-written summary
RFS over-expression increased biomass.
- Treatment
- over expression of raffinose synthase (RFS)e0
- Gene
- raffinose synthase (RFS)e0
- Outcome
- biomasse0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“over expression of raffinose synthase (RFS) resulted in increased biomass”
t0“hybrid poplar”
Claim · model-written summary
RFS over-expression increased total cellulose content.
- Treatment
- over expression of raffinose synthase (RFS)e0
- Gene
- raffinose synthase (RFS)e0
- Outcome
- total cellulose contente0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“over expression of raffinose synthase (RFS) resulted in increased biomass and total cellulose content”
t0“hybrid poplar”