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Wood Development Group Institute of Biotecnology Viikinkaari 1 (P.O.Box 65)
00014 University of Helsinki
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Tel: +358-9-1911
fax +358-9-1915 9366

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Yrjö Helariutta
+358-9-191 59422

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Betula pendula and Populus trichocarpa

It is also important to investigate wood development in a real tree species, in our case the silver birch (Betula pendula) and poplar (Populus trichocarpa). It is important to investigate how well the information from Arabidopsis procambium development is actually applicable to the context of cambium development in a tree system.

B. pendula is a dominating deciduous tree species in Finland and it is extensively used for example in paper, pulp, furniture and plywood industries.
There are many reasons why we have chosen Betula pendula as our model tree species: it is diploid with a relatively small genome size (approximately 400 Mb - only four times that of Arabidopsis!) and basic molecular techniques have been established for work on this tree species. Moreover, it is compatible with genetic work; it is monoecious and the generation time on this tree species can be pushed up to one year or so. We are investigating wood development in birch by two approaches:

1. The role of CRE1/WOL like genes in birch and Populus
Since WOL is the first molecule specifically implicated in the control of the proliferation of the vascular tissue, it is important to investigate whether WOL like genes and corresponding putative signal transduction pathways have a role in an analogous process regulating the cambial activity of a tree. This is especially relevant hypothesis, since we have already determined that the pattern of the WOL-dependent cell divisions around the developing xylem in the Arabidopsis root has an intriguing parallelism to the pattern of the cambial cell divisions between phloem and xylem in a tree (Mähönen et al. 2000). Furthermore, as a more direct evidence, we have recently identified WOL-like genes, which are active in the cambial zone of the trunk of the silver birch tree. This information is very suggestive for a common basis of the control of cell proliferation both in Arabidopsis root tip and in a trunk of a tree. Our future research activity is focused on the deeper analysis of this parallelism.

2. Functional genomics of wood development
We have recently (in collaboration with Drs. Tapio Palva, Jaakko Kangasjärvi and Lars Paulin of the Institute of Biotechnology) initiated a functional genomics approach in birch. My group has recently identified (as Expressed Sequence Tags, ESTs) some 20 000 genes active in the context of wood formation in birch (we are currently carrying out the annotation of these genes). When we know the detailed spatial and temporal pattern of the WOL like genes, it is possible to approach the identification of their target effectors by searching for identical pattern of expression in microarrays.