Making poplars more popular

Trees of the populus genus - poplars to you and me - grow freely throughout the Northern hemisphere. Arabidopsis, on the other hand, is a small flowering plant that is widely used as a model organism in plant biology. It is a member of the mustard (Brassicaceae) family, which includes cultivated species such as cabbage and radish. Arabidopsis is not of major agronomic significance, but it offers important advantages for basic research in genetics and molecular biology. A point not lost on Dr Catherine Perrot-Rechenmann. Dr Perrot-Rechenmann is co-ordinating the 'POPWOOD' project and the humble arabidopsis plays a key role in the team's efforts to improve the properties of the poplar tree as a cash crop in European silviculture, using genetic engineering techniques.
But why poplar, and why arabidopsis? "Poplar is rapid growing, will prosper virtually anywhere in Europe, and its timber is almost perfect for the production of pulp for the paper industry," explains Dr Perrot-Rechenmann. "The important word here, though, is 'almost'. It doesn't quite get top marks. As a result, Europe imports huge quantities of eucalyptus, which fits the bill perfectly." How then, can arabidopsis help? "It is one of the few plants that has been fully genomically mapped," she says, "and although it bears little physical similarity to the poplar, genetically, it is very close. It has a very quick 'seed-to-seed' cycle time - just six weeks - and therefore represents a fertile source of genetic material. Using it as a source of novel genetic resources, we believe that we can improve the poplar, to the benefit of foresters throughout Europe."

Taming the gene genie

A noble aim. There are, however, widespread - and probably well-founded - worries of genetically modified species cross-pollinating with neighbouring crops, producing unwanted hybrids. "Not a problem," Dr Perrot- Rechenmann reassures us. "Our plan is to produce a poplar crop that can be harvested at the age of seven years - before it flowers for the first time, so no contamination is possible. Doing this, we even avoid the need to replant. The stump of a young tree, when felled, will simply start over again and produce new growth."
It is a question of modifying the vascular system - the fluid conducting mechanism that helps govern the features of all life as we know it. In particular, the scientists involved in this project are investigating the properties of vascular tissues, such as outer wall thickness and xylem cells (the primary water transport and wood-forming units). If they are right, they could alter fibrillar nature of poplar cells so that the tree could be tailored to give just the right properties to make it an attractive crop.

Soft cell, hard cell?

Work is progressing well, and the team is confident it can succeed. The breadth of the project does not, however, stop there. "Our colleagues in Sweden have been working hard on perfecting software modelling techniques," explains Dr Perrot-Rechenmann. "These should allow us to use young cells, apply three-dimensional simulation algorithms, and develop computer images of the cell structure of a mature tree, based on evidence available from young specimens. We have vastly improved our knowledge of vascular development and wood formation, and we can now engineer transgenic poplars with enhanced fibre and wood properties."
The technology is still in its infancy. "We still have a long way to go," admits Dr Perrot- Rechenmann, "before the results of this project have a significant impact on the European citizen. What we have learned so far, though, leads us to believe that young trees - just a few years old - can be a viable crop."
In the meantime, the partners are busy preparing the path towards future commercial implementation of their results. They have selected genes that regulate vascular properties, manipulated vascular development within hybrids, and evaluated the properties of the fibres produced by these transgenic lines.
Does this all sound a little frightening? Perhaps. But do not be too concerned. Breeders of domestic animals have been doing this since the Stone Age. Prime specimens have always been mated with other best of breeds. The workers in this project are simply speeding up the process for trees.

Results:

We have completed our screen of mutant libraries having screened 4000 Landsberg erecta and 2000 Columbia M2 mutant plants. The screen was carried out entirely using chemically (ethyl methyl sulphonate) mutagenised plants. Large scale expression analysis on microarrays using poplar ESTs has provided invaluable information on the pattern of expression of about 6000 EST. Knock out mutants have been identifi ed within the LAX gene family by screening of the SLAT Arabidopsis populations. Research in wood and fi bres has been limited by lack of effi cient measurement methods. A set of characterisation methods has been established, useful in tree improvement programs for evaluation of properties of young hardwood, materials (P6).