13 ERA-CAPS PER-ASPERA Frigerio

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The plant endomembrane system underpins virtually every aspect of plant life and feeds every one of us, because it is the 'factory' where proteins and lipids for animal and human nutrition are produced. It is a system of interconnected, membrane-bounded compartments within the cell, forming a metabolic continuum called the secretory pathway. A major component is the endoplasmic reticulum (ER), which is the port of entry of the secretory pathway. The ER is a network of tubular membranes involved in the synthesis, assembly, quality control and export of proteins to other compartments of the secretory pathway. The ER is also a major site for the synthesis of lipids and is present in all eukaryotes, but has unique features in plant cells: it can act as a storage compartment for proteins (like in maize seeds) and lipids (like in oilseed crops such as sunflower). The ER is a very dynamic structure and can change its shape in order to accommodate these diverse functions. However, we do not know why the unique architecture of the ER is necessary for its function. Nothing is known about the factors that regulate plant ER shape and how its shape determines how much protein and lipid the ER can synthesise and/or store. Over the past 5 years we have made some important discoveries on the mechanisms that may help regulate the organisation of this important structure. We have discovered that a family of proteins called reticulons can induce changes in the shape of the plant ER network, thereby affecting its function. Also we have identified some proteins which are good candidates as regulators of ER network branching, tubule fusions and anchoring. To help our studies, we have contributed to developing a computerised mapping system for analysing the dynamics of the ER. In essence, we now know the ingredients required to build the architecture of the ER. What we don't yet know is how these ingredients come together to determine it.In this transnational project, we propose to investigate the nature and interactions of the proteins that anchor the ER network to other organelles, and the proteins that permit new ER tubules to form, to grow and fuse with existing tubules. We will study how changing the expression of these proteins affects the synthesis and transport of lipid storage proteins, especially in cereal seeds. Understanding the function of these key regulators will allow us to redesign the ER in order to improve its capacity to make proteins and lipids in seed crops.