1. Dipartimento di Biologia, Universita’ degli Studi di Milano, 20133 Milan, Italy
2. Consiglio Nazionale delle Ricerche Istituto di Biofisica, 20133 Milan, Italy
3. Department of Molecular Biosciences, University of Oslo, N-0316 Oslo, Norway
4. Department of Molecular Mechanisms of Phenotypic Plasticity, Institut de Biologie Moléculaire des Plantes du Centre National de la Recherche Scientifique, Université de Strasbourg, F-67084 Strasbourg Cedex, France