1. Department of Biology, Indiana University, Bloomington, IN 47405, USA.
2. School of Biosciences, University of Nottingham, Loughborough LE12 5RD, UK.
3. Umeå Plant Science Centre, SLU, Umeå, Sweden.
4. School of Computer Science and Information Technology, University of Nottingham, Nottingham NG7 2UH, UK.