1. Centre de Recherche sur les Macromolécules Végétales (CERMAV-CNRS), BP53, 38041 Grenoble Cedex 9, France, Laboratory of Biochemistry, Institut Químic de Sarrià, Universitat Ramon Llull, 08017 Barcelona, Spain, and School of Biotechnology, Royal Institute of Technology, AlbaNova University Center, 106 91 Stockholm, Sweden