PI: Hannele Tuominen

Staff: Charleen Moreau, PhD student

Background

Wood density is one of the most important wood properties determining the end use of wood. Wood density is largely determined by the thickness of the secondary cell walls of fibers. Cell-wall thickness displays great variation and is under fairly strong genetic control, implying that great gains in wood density could be achieved through genetic breeding. Formation of the cell wall and the final thickness of the wall is a complex biochemical process, which is influenced by both environmental and genetic factors. Cell wall thickness has been shown to correlate positively with the duration of the cell wall formation, and it seems that it is the duration and the life-time of xylem elements rather than the rate of cell wall formation that determines the thickness of the cell walls. The life-time of xylem elements and therefore the duration of cell wall formation is determined by programmed cell death (PCD) of the xylem elements. Programmed cell death is a genetically controlled process aimed at elimination of harmful cells in plants as well as in animals and unicellular organisms.

Aims

This FuncFiber project aims to provide tools to modify wood density by targeting the PCD process in xylem fibers of Populus trees. To accomplish this task, information is needed on candidate genes that regulate fiber PCD. Candidate regulatory genes have been identified from an existing microarray data from woody tissues of Populus, and selected genes will be functionally tested in transgenic Populus trees as well as in Arabidopsis thaliana. Functional analysis of two selected candidate genes, a beta-glucosidase and a metacaspase, has already been initiated. Identification of fiber cell death regulatory genes allows transgenic modifications to test whether longer life time of xylem fibers, by extension of the cell wall deposition phase, increases wood density. Such genes are suitable targets for forest biotechnology purposes towards improved wood properties and as molecular markers in traditional forest tree breeding.