My research focuses on lignification and cell death of xylem elements and how these processes influence the chemical and physical properties of the secondary cell walls and woody tissues of vascular plants. We use two model systems. The roots and hypocotyls of Arabidopsis thaliana provide excellent models for understanding the molecular and genetic control of xylem differentiation, while the woody tissues of aspen (Populus tremula) trees are practical for high-resolution gene expression, genetic, genomic and functional assays.

Xylem elements mature by depositing cellulose-rich secondary cell walls until they die through programmed cell death. Cell death therefore controls the thickness of the secondary cell walls of the xylem by controlling the life time of the xylem elements. We have earlier shown that cell death also controls lignification of xylem elements. Work done in the Zinnia elegans tracheary element differentiation system revealed that lignin biosynthesis continues even after cell death and that lignin polymerization occurs only after cell death. This sequence of events needs to be strictly controlled in time and place. In my previous work I have characterized the cell death process and identified factors that control both lignification and cell death of the xylem elements. The current aim is to identify factors that initiate and execute xylem cell death. One of the focus areas is the signaling and functional characterisation of the Arabidopsis thaliana metacaspase gene family using reverse genetic, forward genetic and biochemical methods in intact plants and in ectopic, hormonally induced tracheary elements.

The fact that the lifetime of the xylem elements controls the thickness of the cell walls and hence the extent of biomass production within each cell implies that that the identification of cell death controlling factors could be used to modify overall biomass production in forest trees. We have taken two different approaches to investigate the relationships between xylem maturation, the chemical and physical properties of the secondary cell wall and the properties of wood. The first approach is to modify expression of selected candidate genes in transgenic aspen (Populus tremula) trees using cell-specific promoters, newest DNA editing technologies and tree phenotyping platform with the aim of delaying xylem cell death and thereby improving biomass properties. The second approach takes advantage of the natural variation within a Swedish aspen population with the aim to identify variation in the secondary cell wall and wood properties and the underlying molecular mechanism by genome-wide association mapping.

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