Starch metabolism in leaves:

We aim to understand the nature and regulation of the pathways of starch synthesis and degradation in leaves. Most of our work is on Arabidopsis, in which we have taken both forward and reverse genetic approaches to identify important components of the pathways, and to discover how flux through the pathway of starch degradation is controlled. We work in close collaboration with Sam Zeeman and colleagues (ETH, Zurich) and with others including Jychian Chen (Academia Sinica, Taipei) and Martin Steup and colleagues (University of Potsdamhttp://www.bio.uni-potsdam.de/professuren/pflanzenphysiologie).

Work on starch degradation is being extended to other species, in collaboration withTrevor Wang and colleagues.

Current research in the Smith lab includes:

• Nature and regulation of the primary attack on the starch granule during starch degradation.
• The metabolism in the cytosol of products of starch degradation exported from the chloroplast.
• Importance of starch synthase isoforms in starch synthesis.
• Control of the onset and the rate of starch degradation at night

TOP: Transient expression in tobacco leaves of a GFP-tagged version of phosphatase (LSF: Like SEX4) necessary for normal rates of starch degradation in Arabidopsis leaves. Left: GFP fluorescence. Centre: chlorophyll fluorescence. Right: merged picture. The LSF protein is confined to the surface of starch granules within the chloroplast. Bar is 5 µm. (Sylviane Comparot-Moss).

BOTTOM: Iodine-stained starch granules in chloroplasts of leaf cells of a wild-type plant which has about 80 chloroplasts per cell (left), and an arc6 mutant which has only about two giant, convoluted chloroplast per cell (right). Chloroplasts of wild-type plants contain about 5 starch granules whereas chloroplasts of arc6 contain many more, but the number per unit chloroplast is almost identical in the two lines (Tilly Crumpton-Taylor).

Recent relevant publications:

Zeeman SC, Tiessen A, Pilling E, Kato L, Donald AM, Smith AM (2002) Starch synthesis in Arabidopsis. Granule synthesis, composition and structure. Plant Physiol. 129, 516-529.
Niittylä T, Messerli G, Trevisan M, Chen J, Smith AM, Zeeman SC (2004) A novel maltose transporter essential for starch degradation in leaves. Science 303, 87-89.

Chia T, Thorneycroft D, Chapple A, Messerli G, Chen J, Zeeman SC, Smith SM, Smith AM (2004) A cytosolic glucosyltransferase is required for conversion of starch to sucrose in Arabidopsis leaves at night. Plant J. 37, 853-863.

Smith SM, Fulton DC, Chia T, Thorneycroft D, Chapple A, Dunstan H, Hylton C, Zeeman SC, Smith AM (2004) Diurnal changes in the transcriptome encoding enzymes of starch metabolism provide evidence for both transcriptional and posttranscriptional regulation of starch metabolism in Arabidopsis leaves. Plant Physiol. 136, 2687-2699.

Zeeman SC, Thorneycroft D, Schupp N, Chapple A, Weck M, Dunstan H, Halidmann P, Bechtold N, Smith AM, Smith SM (2004) Plastidial α-glucan phosphorylase is not required for starch degradation in Arabidopsis leaves but has a role in the tolerance of abiotic stress. Plant Physiol. 135, 849-858.

 Zeeman SC, Smith SM, Smith AM (2004) The breakdown of starch in leaves. New Phytol. 163, 247-261.

 Yu TS, Zeeman SC, Thorneycroft D, Fulton DC, Dunstan H, Lue WL, Hegemann B, Tung SY, Umemoto T, Chapple A, Tsai DL, Wang SM, Smith AM, Chen J, Smith SM (2005) α-amylase is not required for breakdown of transitory starch in Arabidopsis leaves. J. Biol. Chem. 280, 9773-9779.

 Smith AM, Zeeman SC, Smith SM (2005) Starch degradation. Annu. Rev. Plant Biol. 56, 73-97.

 Fettke J, Chia T, Eckermann N, Smith AM, Steup M (2006) A transglucosidase necessary for starch degradation and maltose metabolism in leaves acts on cytosolic heteroglycans. Plant J. 46, 668-684.

 Niittylä T, Comparot-Moss S, Lue WL, Messerli G, Trevisan M, Seymour MDG, Gatehouse JA, Villadsen D, Smith SM, Chen J, Zeeman SC, Smith AM (2006) Similar protein phosphatases control starch metabolism in plants and glycogen metabolism in animals. J. Biol. Chem. 281, 11815-11818.

 Zeeman SC, Smith SM, Smith AM (2007) The diurnal metabolism of leaf starch. Biochem. J. 401, 13-28

Smith, AM, Stitt M (2007) Coordination of carbon supply and plant growth. Plant Cell Env. 30, 1128-1149. 

Fulton DC, Stettler M, Mettler T, Vaughan CK, Li J, Franscisco P, Gil M, Reinhold H, Eicke, S, MesserliG, Dorken G, Halliday K, Smith AM, Smith SM, Zeeman, S.C. (2008) β-AMYLASE4, a noncatalytic protein required for starch breakdown, acts upstream of three active β-amylases in Arabidopsis chloroplasts. Plant Cell 20, 1040-1058.

 Kötting O, Santelia D, Edner C, Eicke S, Marthaler T, Gentry MS, Comparot-Moss S, Chen J, Smith AM, Steup M, Ritte G, Zeeman SC (2009) STARCH-EXCESS4 is a laforin-like phosphoglucan phosphatase required for starch degradation in Arabidopsis thaliana. Plant Cell, 21: 334-346.