Universitas Helsingiensis

Growth in the trees

Growth in the treesStem cell research of forest trees provides valuable information about stem cells that can be utilised by other fields of science. In the forest industry, the new gene information could be applied to accelerating traditional tree breeding.

Stem cells in plants and animals have many characteristics in common. Human stem cells form the various organs, and plants also have their own stem cells that are responsible for the growth of the plant and the formation of various structures.

“The vascular cambium, the ‘zone’ of living stem cells in a tree, is a layer between the bark and the wood similar to human stem cells in the bone marrow.

The undifferentiated cells divide and form daughter cells and thus generate growth and biomass. However, the daughter cells differentiate into new cell types, partly into xylem or the phloem tissue of bark,” says Professor Yrjö Helariutta from the Institute of Biotechnology at the University of Helsinki.

The group led by Professor Helariutta is conducting research in stem cells responsible for wood formation in forest trees. So far, relatively little is known about stem cells, whether human or plant. However, they are a universal biological phenomenon, and research into them will give a broader understanding of stem cells.

“We’re currently studying how genes control wood formation. Our special focus of interest is how stem cells in the vascular cambium work: what makes them remain as undifferentiated stem cells and what makes them divide? We are also trying to understand what makes the daughter cells generated as a result of vascular cambium division differentiate partly into xylem or phloem tissue that transports assimilation products.”

The research has shown that the growth hormone cytokinin plays a key role in maintaining the stem cells in the vascular cambium. While it also stimulates cell division in the vascular cambium, gene functions that counteract the effect of cytokinin are required for the differentiation of xylem.

“We have also discovered a gene that regulates whether a daughter cell that has divided from the vascular cambium develops into phloem or xylem. In recent years, we have embarked on examining what these different events of determination of cell identities mean at the molecular level,” says Professor Helariutta.

Natural tree improvement using genes

The research also aims at mapping out how the knowledge being gained can be applied in practice, such as in forest tree improvement. The objective is to apply the knowledge so that instead of gene transfers, it would be possible to accelerate traditional tree breeding through new information on genes. “This could have broader implications for agriculture.”

Earlier, tree breeding was based on biological phenomena whose mechanisms were relatively poorly known. The new knowledge could be used to improve quickly growing trees. This would also have ecological implications because fast-growing forests would reduce the need to conquer areas still in a natural state. So far, Finnish forest industry companies have shown no interest in participating in the research because they receive adequate supplies of wood such as from the natural forests in Karelia and moreover, they do this without opposition. Gene research also carries repercussions that do not auger well for paper sales worldwide.

Nevertheless, gene research also makes it possible to improve trees naturally. Professor Helariutta gives an example: “Genes affect the raw material properties of wood, such as the amount of cellulose or density. The properties of fibres generated during the differentiation of wood play a significant role in paper manufacturing because cellulose and lignin accumulate on the walls of the fibres. Cellulose is a well-known desired polymer whereas lignin is not because it colours the paper yellow. Gene transfers can be used to modify and reduce lignin concentrations, and this has already been done in Central Europe. We on the other hand are finding out how lignin concentrations could be reduced using traditional methods by selecting trees that carry a gene mutation that leads to lower lignin concentrations.”

In principle, it would be possible to already start applying accumulated research knowledge in various tree improvement programmes. The schedule for benefiting from tree improvement largely depends on whether the use of transgenic trees in forest tree improvement will be permitted, particularly in tropical tree plantations.

“If gene transfer could be used soon, applications could be within our grasp within 5–10 years. Tree improvement based on traditional selection does not use gene transfers, so it will most likely take 10–20 years.”

Exciting research

In Finland, research into the molecular biology of plants has rapidly risen to a high standard, one proof of which is the considerable incentive awarded to Professor Helariutta in 2005 by the European Young Investigator Award scheme. Thirteen people are currently working in Professor Helariutta’s group, six of them post doctoral fellows. Six nationalities are represented in the research group and its work has aroused a good deal of interest worldwide. Professor Helariutta is a highly popular speaker around the world and his research findings have been published in prominent forums, such as Nature and Science.

Moreover, the group has received several applications from foreign post doctoral researchers, some of whom have been funded by foreign and international sources.

Dr Anthony Bishopp from Britain has worked in Professor Helariutta’s group since July 2004. “I came to work here because it is a group which does exciting research and has an excellent record. Also the funding situation is pretty good, enabling us to perform the experiments that we want to rather than only those we can afford.”

Dr Bishopp is researching genetic factors controlling the differentiation of xylem, which is a major component of wood. “I have two projects running, the first is a slightly more classical approach where I have a mutant impaired in xylem development and I’m trying to characterise which gene is affected and how exactly the plant is impaired. The second project involves setting up a new technique to identify xylem specific genes and how they are regulated,” says Dr Bishopp.

Rather than broadly based research, Professor Helariutta takes the view that it is more productive to focus expressly on a more specialised field and to find one’s own path and follow it through in a consistently and logically way.

“The genetic foundation of various phenomena in the plant kingdom has been uncovered over the past 15 years. I came into the field at precisely the right time – when the gene map was being built. Now we’re at a stage that corresponds to the era of the voyages of discovery,” he says.

Arja-Leena Paavola