1. Department of Plant and Environmental Sciences, The Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, 91904 Jerusalem, Israel
2. Fachbereich Biologie, Universität Konstanz, D-78457 Konstanz, Germany
3. Department of Microbiology & Molecular Genetics, Biomedical Physical Sciences, Michigan State University, East Lansing, MI 48824-4320, USA