1. John Innes Centre, Norwich NR4 7UH, UK.
2. USDA Forest Products Laboratory, 1 Gifford Pinchot Drive, Madison, WI 53726, USA.
3. Institute of Molecular Plant Sciences, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JH, UK.
4. Laboratoire de Physiologie Cellulaire Végétale, CNRS, CEA, INRA, and Université Joseph Fourier, F-38000 Grenoble, France