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Dynamics of ER Protein Export in Plant Cells

Plants are major players in the biotechnology boom for production of a wide range of compounds. If we are to fully exploit plants as living factories, we must understand the mechanics of the production process.

Plants are dynamic systems—they virtually hum with activity at the molecular level. Each cell is a tiny factory, building materials according to instructions provided by DNA. Using genetic means, plants can be coaxed into producing valuable compounds. These are built and packaged in a series of dynamic cell compartments, comparable to an assembly line in a factory. These compartments, collectively named the secretory pathway, are essential to the life of a cell.

Organelles that make up the secre­tory pathway are in a constant state of exchanging molecules, such as proteins, lipids, and sugars. Secretory proteins are synthesized in the endoplasmic reticulum (ER), then transported forward to a processing compartment, the Golgi apparatus, to be distributed to the plasma membrane or the vacuole. Forward traffic of macromolecules is counterbalanced by retrograde transport between organelles to allow homeostasis of membrane and resident proteins. Despite intense communication, secretory organelles maintain their morphological and functional identity. How they achieve this is mostly unknown.

The research in our laboratory focuses on the investigation of how secretory molecules are packaged and which mechanisms regulate the shipment of compounds to the final destination. We also explore the mechanisms that lead to the establishment and maintenance of organelles of the secretory pathway. The analysis of these topics will give clues to key biological questions on the plant secretory pathway and will provide a better understanding of mechanisms that govern the steps of secretion in plants to enable us to regulate cell secretion and to acquire genetic tools that may lead to better management of natural resources.

Our understanding of the plant secretory pathway has often been hampered by the lack of adequate investigative techniques. In our laboratory we employ fluorescent protein technology combined with advanced imaging technology to investigate dynamics of the plant secretory pathway. These new investigative imaging techniques allow us to watch the secretory pathway in living plant cells in real time.

Figure 1. Confocal image of a tobacco leaf epidermal cell co-expressing a fluorescent Golgi marker (pseudocolored red) and a fluorescent marker that labels the actin cytoskeleton (pseudo­colored green).

Selected Publications From the Past Five Years

Hanton SL, Chatre L, Renna L, Matheson LA, Brandizzi F (2008) Plant Sar1 isoforms with near-identical protein sequences exhibit different localisations and effects on secretion. Plant Mol Biol, in press

Matheson LA, Suri SS, Hanton SL, Chatre L, Brandizzi F (2008) Correct targeting of plant ARF GTPases relies on distinct protein domains. Traffic 9: 103-120

Hanton SL, Chatre L, Matheson LA, Renna L, Brandizzi F (2007) De novo formation of plant endoplasmic reticulum export sites is membrane cargo induced and signal mediated. Plant Physiol 143: 1640-1650

Matheson LA, Hanton SL, Rossi M, Latijnhouwers M, Stefano G, Renna L, Brandizzi F (2007) Multiple roles of ARF1 in plant cells include spatially-regulated recruitment of coatomer and elements of the Golgi matrix. Plant Physiol 143: 1615-1627

Zhou Y, Niu H, Brandizzi F, Fowke LC, Wang H (2006) Molecular control of nuclear and subnuclear targeting of the plant CDK inhibitor ICK1 and ICK1-mediated nuclear transport of CDKA. Plant Mol Biol 62: 261-278

Matheson LA, Hanton SL, Brandizzi F (2006) Traffic between the plant endoplasmic reticulum and Golgi apparatus: to the Golgi and beyond. Curr Opin Plant Biol 9: 601-609

Stefano G, Renna L, Hanton SL, Chatre L, Haas TA, Brandizzi F (2006) Arl1 plays a role in the binding of the GRIP domain of a peripheral matrix protein to the Golgi apparatus in plant cells. Plant Mol Biol 61: 431-449

Dunkley TP, Hester S, Shadforth IP, Runions J, Weimar T, Hanton SL, Griffin JL, Bessant C, Brandizzi F, Hawes C, Watson RB, Dupree P, Lilley KS (2006) Mapping the Arabidopsis organelle proteome. Proc Natl Acad Sci USA 103: 6518-6523

Stefano G, Renna L, Chatre L, Hanton SL, Moreau P, Hawes C, Brandizzi F (2006) In tobacco leaf epidermal cells, the integrity of protein export from the endoplasmic reticulum and of ER export sites depends on active COPI machinery. Plant J 46: 95-110

Hanton SL, Matheson LA, Brandizzi F (2006) Seeking a way out: export of proteins from the plant endoplas­mic reticulum. Trends Plant Sci 11: 335-343

Hanton SL, Renna L, Bortolotti LE, Chatre L, Stefano G, Brandizzi F (2005) Di-acidic motifs influence the export of transmembrane pro­teins from the endoplasmic reticu­lum in plant cells. Plant Cell 17: 3081-3093

daSilva LL, Taylor JP, Hadlington JL, Hanton SL, Snowden CJ, Fox SJ, Foresti O, Brandizzi F, Denecke J (2005) Receptor salvage from the prevacuolar compartment is essen­tial for efficient vacuolar protein targeting. Plant Cell 17: 132-148

Rutherford S, Brandizzi F, Townley H, Craft J, Wang Y, Jepson I, Martinez A, Moore I (2005) Improved transcriptional activators and their use in mis-expression traps in Arabidopsis. Plant J 43: 769-788

Chatre L, Brandizzi F, Hocquellet A, Hawes C, Moreau P (2005) Sec22 and Memb11 are v-SNAREs of the anterograde endoplasmic reticulum-Golgi pathway in tobacco leaf epidermal cells. Plant Physiol 139: 1244-1254

Renna L, Hanton, SL, Stefano G, Bortolotti L, Misra V, Brandizzi F (2005) Identification and characterization of AtCASP, a plant transmembrane Golgi matrix protein. Plant Mol Biol 58: 109-122

Hanton SL, Bortolotti LE, Renna L, Stefano G, Brandizzi F (2005) Crossing the divide—transport between the endoplasmic reticulum and Golgi apparatus in plants. Traf­fic 6: 267-277

Kotzer AM, Brandizzi F, Neumann U, Paris N, Moore I, Hawes C (2004) AtRabF2b (Ara7) acts on the vacu­olar trafficking pathway in tobacco leaf epidermal cells. J Cell Sci 117: 6377-6389

daSilva LL, Snapp EL, Denecke J, Lippincott-Schwartz J, Hawes C, Brandizzi F (2004) Endoplasmic reticulum export sites and Golgi bodies behave as single mobile secretory units in plant cells. Plant Cell 16: 1753-1771

Evans DE, Irons SL, Debela MH, Bran­dizzi F (2004) The nuclear envelope in the plant cell cycle. Symp Soc Exp Biol 56: 229-244

Handford MG, Sicilia F, Brandizzi F, Chung JH, Dupree P (2004) Arabi­dopsis thaliana expresses multiple Golgi-localised nucleotide-sugar transporters related to GONST1. Mol Gen Genomics 272: 397-410

Brandizzi F, Hawes C (2004) A long and winding road: symposium on membrane trafficking in plants. EMBO Rep 5: 245- 249

Brandizzi F, Irons SL, Johansen J, Kotzer A, Neumann U (2004) GFP is the way to glow: bioimaging of the plant endomembrane system. J Microsc 214: 138-158

Hawes C, Brandizzi F (2004) The Golgi apparatus—still causing problems after all these years! Cell Mol Life Sci 61: 131-132

Ward TH, Brandizzi F (2004) Dynam­ics of proteins in Golgi membranes: comparisons between mammalian and plant cells highlighted by pho­tobleaching techniques. Cell Mol Life Sci 61: 172-185

Brandizzi F, Hanton S, DaSilva LL, Boevink P, Evans D, Oparka K, Denecke J, Hawes C (2003) ER quality control can lead to retro­grade transport from the ER lumen to the cytosol and the nucleoplasm in plants. Plant J 34: 269-281

Brandizzi F, Saint-Jore C, Moore I, Hawes C (2003) The relationship between endomembranes and the plant cytoskeleton. Cell Biol Int 27: 177-179

Irons SL, Evans DE, Brandizzi F (2003) The first 238 amino acids of the human lamin B receptor are targeted to the nuclear envelope in plants. J Exp Bot 54: 943-950

Neumann U, Brandizzi F, Hawes C (2003) Protein transport in plant cells: in and out of the Golgi. Ann Bot (Lond) 92: 167-180

Zhou Y, Li G, Brandizzi F, Fowke LC, Wang H (2003) The plant cyclin-dependent kinase inhibitor ICK1 has distinct functional domains for in vivo kinase inhibition, protein instability and nuclear localization. Plant J 35: 476-489

Sparkes IA, Brandizzi F, Slocombe SP, El-Shami M, Hawes C, Baker A (2003) An Arabidopsis pex10 null mutant is embryo lethal, implicat­ing peroxisomes in an essential role during plant embryogenesis. Plant Physiol 133: 1809-1819

Brandizzi F, Fricker M, Hawes C (2002) A greener world: the revolu­tion in plant bioimaging. Nat Rev Mol Cell Biol 3: 520-530

Brandizzi F, Snapp EL, Roberts AG, Lippincott-Schwartz J, Hawes C (2002) Membrane protein transport between the endoplasmic reticulum and the Golgi in tobacco leaves is energy dependent but cytoskeleton independent: evidence from selec­tive photobleaching. Plant Cell 14: 1293-1309

Brandizzi F, Frangne N, Marc-Martin S, Hawes C, Neuhaus JM, Paris N (2002) The destination for single-pass membrane proteins is influenced markedly by the length of the hydrophobic domain. Plant Cell 14: 1077-1092

Saint-Jore CM, Evins J, Batoko H, Brandizzi F, Moore I, Hawes C (2002) Redistribution of membrane proteins between the Golgi apparatus and endoplasmic reticulum in plants is reversible and not depen­dent on cytoskeletal networks. Plant  J 29: 661-678

Hawes C, Saint-Jore CM, Brandizzi F, Zheng H, Andreeva AV, Boevink P (2001) Cytoplasmic illuminations: in planta targeting of fluorescent proteins to cellular organelles. Pro­toplasma 215: 77-88

Tormakangas K, Hadlington JL, Pimpl P, Hillmer S, Brandizzi F, Teeri TH, Denecke J (2001) A vacuolar sort­ing domain may also influence the way in which proteins leave the endoplasmic reticulum. Plant Cell 13: 2021-2032

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