1. Department of Plant Systems Biology, Flanders Institute for Biotechnology, 9052 Gent, Belgium
2. Department of Molecular Genetics, Ghent University, 9052 Gent, Belgium
3. Angewandte Holzbiologie, Technische Universität München, 80797 München, Germany
4. Umeå Plant Science Center, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden