Sucrose metabolism:
We aim to understand the pathway of sucrose metabolism in the non-photosynthetic cells of plants. Non-photosynthetic cells are dependent for metabolism and growth on carbon from imported sucrose. Only two classes of enzymes in plants can catalyse the entry of carbon from sucrose into cellular metabolism: sucrose synthases and invertases. Most of the biomass on the planet – and almost all of the material we harvest as food crops – consists of carbon metabolised via these two enzymes. It has been generally accepted that sucrose synthases are central, “housekeeping” enzymes, whereas invertases have a variety of specific roles in particular conditions and organs.
We have discovered recently that this perception is incorrect (Barratt et al., 2009). Using knockout mutants of Arabidopsis we have demonstrated first that sucrose synthase (SUS) is largely dispensable except in specific developmental and environmental contexts, and second that specific isoforms of neutral, cytosolic invertase (CINV) are essential for normal growth and development.
Work on sucrose synthases and invertases is in collaboration with Nick Kruger (University of Oxford). Our work is closely linked to that of Trevor Wang and colleagues, who are studying these enzymes in the model legume Lotus japonicus.
Plants: wild-type (left) and cinv1/cinv2 mutant (right) plants of the same age. The cinv1/cinv2 mutant carries T-DNA insertions in genes encoding two isoforms of invertase located in the cytosol.
Root sections: wild-type (left) and cinv1/cinv2 mutant (right). Cellular structure is disorganised and starch is almost absent from the root cap in the mutant.
Relevant publications:
Barratt DHP, Barber L, Kruger NJ, Smith AM, Wang TL, Martin C (2001) Multiple, distinct soforms of sucrose synthase in pea. Plant Physiol. 127, 655-664.
Bieniawska Z, Barratt DHP, Garlick AP, Thole V, Kruger NJ, Martin C, Zrenner R, Smith AM (2007) Analysis of the sucrose synthase gene family in Arabidopsis. Plant J. 49, 810-828.
Barratt DHP, Derbyshire P, Findlay K, Pike M, Wellner N, Lunn J, Feil R, Simpson C, Maule A, Smith AM (2009) Normal growth of Arabidopsis plants requires cytosolic invertase but not sucrose synthase. Proc. Natl Acad. Sci. USA, doi:10.1073/pnas.0900689106.
