1. Department of Biochemistry, University of Cambridge, Hopkins Building, Downing Site, Tennis Court Road, Cambridge CB2 1QW, UK
2. The Commonwealth Scientific and Industrial Research Organisation (CSIRO), Division of Plant Industry, Canberra, Queensland, Australia
3. Department of Plant Sciences, University of Cambridge, Downing Site, Downing Street, Cambridge CB2 3EA, UK
4. Department of Chemical Engineering, Centre for Bioprocess Engineering Research, University of Cape Town, Rondebosch 7701, Cape Town, South Africa
5. School of Biological Sciences, University of Bristol, Life Sciences Building, Downing, 24 Tyndall Avenue, Bristol BS8 1TQ, UK