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 break¬through 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 ligno- cellolusic processes. To study this, different proteomics techniques have been explored and developed.
Reactive oxygen species (ROS)
ROS have recently been suggested to act as signaling molecules in the control of specialized processes, such as plant growth and defense, hormonal signaling, 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. Thorough 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 using multivariate methods in combination with data from metabolomic and transcriptomic platforms.
Linocellulose regulating proteins
In this project we are taking a proteomic approach to answer fundamental questions about cellulose deposition in the second- ary cell wall that are important for chemical and ultra structural properties of xylem fibers in wood. In our focuses to achieve this goal we will explore the structural composition and function of cellulose synthases (CesAs) in the plasma membrane of wood fibers.The project will highly depend on masspectrometry in combination with multivariate statistics and bioinformatics. Another group of proteins that has been identified as central to the regulation of phenylpropanoid metabolism is the MYB tran- scription factor family.Each MYB transcription factor contains a conserved DNA-binding domain, located in the N-terminal part of the protein.One of the intriguing features of PttMYB21a antisense 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.
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 inter- face 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 regula- tory 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 redox mechanisms of this complexr.
- Nilsson R, Bernfur K, Gustavsson N, Bygdell J, Wingsle G, Larsson C. (2010) Proteomics of plasma membranes from leaves, xylem, and cambium/phloem of young poplar trees reveals tissue distribution of transporters, receptors, and proteins involved in wood formation. Molecular & Cell Proteomics 9: 368-387
- Srivastava V, Schinkel H, Witzell J, Hertzberg M, Torp M, Srivastava MK, Karpinska B, Melzer M, Wingsle G (2007) Downregu- lation 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
- Bylesjö M, Nilsson R, Srivastava V, Grönlund A, Johansson AI, Jansson S, Karlsson J, Moritz T, Wingsle G, Trygg J. (2009) In- tegrated 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.
- 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
- Karpinska B, Karlsson M, Srivastava M, Stenberg A, Schrader J, Sterky F, Bhalerao R, Wingsle G (2004) MYB transcription factors are differentially expressed and regulated during secondary vascular tissue development in hybrid aspen. Plant Molecular Biology 56; 255-270.