Gunnar Wingsle - Regulatory Proteins in the Lignification Process in Wood

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Wood is a major source of renewable raw materials that are widely used in the pulp, paper, and timber industries. Poplar has emerged as the model tree for woody species, and molecular tools have been developed that allow breakthrough science in this forest tree. In my research, a major focus has been on proteins that have been shown to play a role in wood development and more specifically in lignin biosynthesis. A major objective has been to develop and use advanced proteomic approaches to study their roles and related biological questions.
Gunnar_Wingsele_portrait

Reactive oxygen species (ROS)
ROS have recently been suggested to act as signalling molecules in the control of specialized processes, such as plant growth and defence, hormonal signalling, and development. Within the project, my group has explored the possibility to alter wood quality by the regulation of ROS at the plasmalemma/cell wall interface using transgenic methodology. A special type of superoxide dismutase with a high isoelectric point (hipI-SOD) has been mainly considered for this genetic manipulation due to its possible role as a regulator of hydrogen peroxide in the polymerization of lignin. Tthorough characterization of this protein in Poplar
has shown that it exists in two isoforms and in an additional spliced form. We are currently using these plants to study the underlying mechanisms of ROS-mediated regulation of cell wall development.
Specific transcription-MYB
Another group of proteins that has been identified as central to the regulation of phenylpropanoid metabolism is the MYB transcription factor family. Each MYB transcription factor contains a conserved DNA-binding domain, located in the N-terminal part of the protein. Some R2R3 MYB proteins bind AC elements in the promoters of several genes of the phenylpropanoid pathway, and thus have been assigned functions in the regulation of phenylpropanoid biosynthesis. For instance, one of these genes, PttMYB21, was found to be much more highly expressed in the secondary cell wall formation zone of xylem and phloem fibres than in other developmental zones. PttMYB21a antisense transgenic plants showed a phenotype with altered growth and elevated levels of total lignin in their vascular tissues. One of the intriguing features of the transgenic plants was the presence of lignin compounds with increased degrees of methoxylation. Moreover, elevated levels of caffeoyl-CoA 3-O-methyltransferase transcripts were found in the transgenic plants, suggesting that PttMYB21a could act as a transcriptional repressor.

The Mediator and close functional relations between the Mediator modules and other transcriptional regulators (from Oudgenoeg et al. unpulished data)

General transcription The Mediator
In all eukaryotes, protein-encoding genes are transcribed by pol II. To perform its most basal functions, pol II requires five general transcription factors (GTFs). It is also now known that a Mediator, a 25 subunit protein complex, functions as a connector between the promoter-bound transcriptional regulators and pol II. The Mediator was first identified in Saccharomyces as an activity required for transcriptional activation in vitro. Later, it was identified as a multiprotein complex that provides an interface for activator and repressor proteins to transmit information from regulatory DNA elements to core promoters. A number of studies have determined that the Mediator is composed of three modules designated as “tail”, “head”, and “middle”. It is important for transcription control, modulating the frequency of initiation in responses to both positive and negative regulatory factors. Surprisingly, prior to our publication (Bäckstrom et al. 2007), there were had been no reports of the Mediator in plants. We are now studying Mediators that seems to play a role in lignin biosynthesis and wood development in Arabidopsis and Poplar.

Svensk sammanfattning

Key publications

Karpinska B, Karlsson M, Srivastava M, Stenberg A, Schrader J, Sterky F, Bhalerao R, Wingsle G (2004) MYB transcrip- tion factors are differentially expressed and regulated during secondary vascular tissue development in hybrid aspen. Plant Molecular Biology 56; 255-270.

Bäckström S, Elfving N, Nilsson R, Wingsle G, Björklund S (2007) Purification of mediator from Arabidopsis thaliana identifies PFT1 as the Med25 subunit. Mol Cell 26: 717-729

Bylesjö M, Nilsson R, Srivastava V, Grönlund A, Johansson AI, Jansson S, Karlsson J, Moritz T, Wingsle G, Trygg J. (2009) Integrated Analysis of Transcript, Protein and Metabolite Data to Study Lignin Biosynthesis in Hybrid Aspen. J. Prot. Res. 8:199-210.

Srivastava V, Srivastav MK, Chibani K, Nilsson R, Melzer M, Wingsle G (2009) Alternative Splicing Studies of the ROS Gene Network in Populus Reveals Two Isoforms of High Iso-electric point Superoxide Dismutase. Plant Physiol. 149: 1848-1859.

Srivastava V, Schinkel H, Witzell J, Hertzberg M, Torp M, Srivastava MK, Karpinska B, Melzer M, Wingsle G (2007) Downregulation of high-isoelectric-point extracellular superoxide dismutase mediates alterations in the metabolism of reactive oxygen species and developmental disturbances in hybrid aspen. Plant J 49: 135-148

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May 2012

Friday, May 18, 2012
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