1 The John Innes Centre, Department of Biological Chemistry, Norwich NR4 7UH, UK. Electronic address: Sarah.O'Connor@jic.ac.uk.
2 Enterprise Institute for Renewable Fuels, Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, MO 63132-2918, USA. Electronic address: TBrutnell@danforthcenter.org.