My main interest is in carbohydrate metabolism and cell wall biosynthesis. In particular I wish to understand how carbohydrate metabolism is coupled to cell wall biosynthesis, especially to the biosynthesis of cellulose. The majority of the biomass accumulation on the planet occurs in the cell walls of non-photosynthetic plant tissues such as the wood of trees. This biomass resource provides the main source of biopolymers in the world, and its importance as renewable resource is likely to increase in the future.
Most of the work in my group addresses genetic factors contributing to stem biomass and wood density. We focus on the molecular mechanisms responsible for carbon allocation to developing wood of trees. The carbon in wood is mostly found in three main cell wall polymers: cellulose, hemicelluloses and lignin. In most plant species, the majority of this carbon is derived from sucrose imported from photosynthetic tissues. Therefore, understanding of sucrose transport to wood and subsequent production of cell wall polymer precursors is central for understanding factors controlling stem biomass and wood density.
Transcriptional regulation clearly plays an important role in these processes, and we are applying different genomics tools to identify transcription factors involved in stem biomass accumulation. We are also working at the interface of wood biology and material science with the aim of using natural variation and modern tree breeding tools to improve the suitability of wood for nanocellulose production. Our plant cell wall and wood research is done with Arabidopsis, aspen and Norway spruce.
|Light microscopy picture of aspen wood fibers and vessels.||Cross section of Arabidopsis stem. Lignified cell walls are shown in red and non-lignified in blue.|
|Cross section of aspen stem.||Siliques of wild type Arabidopsis and opnr-1 showing the seed abortion phenotype (left). Elongated zygotes of wild type and opnr-1 (middle). Confocal microscopy images showing the dual localisation of OPNR in nuclear envelope and mitochondria labelled with PHB3-mCherry (right).|
In addition to wood biology, I have an interest in fundamental cellular processes. Aspen is an excellent model system for many questions in tree biology, but less well suited for investigating plant cell biology. In this context, it is striking that one third of the genes in the most explored model plant Arabidopsis remain of unknown function. We are interested in identifying essential genes, which are indispensable for the function of a plant cell and constitute the minimum gene set required for cellular life. Our ambition is to push new inroads to this unknown territory of plant cell biology. Our approach is to investigate evolutionarily-conserved single copy Arabidopsis genes of unknown function with predominant expression in meristematic cells.
Evolutionarily-conserved single copy genes in flowering plants have been shown to be enriched in essential housekeeping functions. In this project, we recently identified an essential gene we named OPENER (OPNR). opnr mutants show zygotic lethality and endosperm arrest. Intriguingly, OPNR localizes to both nuclear envelope and mitochondria. Connections between subcellular compartments and proteins with dual function is an emerging research frontier in plant cell biology, and OPNR opens a line of investigation into a previously uncharacterized essential process occurring in both nucleus and mitochondria in dividing plant cells.
In our work, we use state-of-the-art tools from molecular biology, biochemistry, genomics, genetics, microscopy, isotope analysis, mass spectrometry and automated plant growth phenotyping.
- Mahboubi A, Linden P, Hedenström M, Moritz T, Niittylä T (2015). Carbon-13 tracking after 13CO2 supply revealed diurnal patterns of wood formation in aspen. Plant Physiology 168: 478-489.
- Gerber L, Zhang B, Roach M, Rende U, Gorzsás A, Kumar M, Burgert I, Niittylä T and Sundberg B (2014). Deficient sucrose synthase activity in developing wood does not specifically affect cellulose biosynthesis, but causes an overall decrease in cell wall polymers. New Phytologist 203: 1220 – 1230.
- Mahboubi A, Ratke C, Gorzsás A, Kumar M, Mellerowicz EJ, Niittylä T (2013). Aspen SUCROSE TRANSPORTER 3 allocates carbon into wood fibers. Plant Physiology 163, 1729-1740.
- Nystedt et al. (2013). The Norway spruce genome sequence gives insights into conifer genome evolution. Nature, 497, 579-584.
- Roach M, Gerber L, Sandquist D, Gorzsas A, Hedenström M, Kumar M, Steinhauser MC, Feil R, Daniel G, Stitt M, Sundberg B and Niittylä T (2012). Fructokinase is required for carbon partitioning to cellulose in aspen wood. Plant Journal, 70, 967 – 977.