The structure and dynamics of the plant endoplasmic reticulum

The structure and dynamics of the plant endoplasmic reticulum (ER) are highly variable, and are thought to be linked to the role of the ER in protein secretion. Neither the mechanisms behind the biogenesis and maintenance of the ER structural components, nor the mechanisms governing the specific functions of the ER structural subdomains have been fully elucidated. One of the primary challenges in the work of understanding these mechanisms is quantifying ER structure and dynamics in order to identify proteins and physiological conditions that affect the ER. The contiguous nature of the ER, alongside the occurrence of ER dynamics over a range of scales and orientations, presents a unique challenge for quantification. This challenge is tackled by creating a software package, AnalyzER, designed to quantify the variations in the structure of the ER and dynamics in response to a variety of ER structural modifying techniques. This package is designed to be as widely applicable as possible, answering a wide variety of questions often posed regarding novel ER resident proteins, whilst also being capable of analysing images generated through a variety of image capture methods. This analysis was used to elucidate the function of novel ER shaping proteins. At the start of this work, two protein families have previously been described as playing a key role in maintaining or modifying plant ER structure: root hair defective 3 (RHD3) a proposed ER fusogen, and the reticulon protein family which mediates ER membrane curvature. Here we introduce a new family of ER shaping proteins: the Lunapark protein family, comprised of AtLNP1 and 2. AtLNP1 localises specifically to ER cisternae whilst AtLNP2 localises throughout the ER structure. Reducing AtLNP1 and 2 transcription results in a reduced proportion of cisternae within the ER whilst over-expression results in cisternae induction, with the cisternae induced by AtLNP1 and 2 possessing different structural characteristics. Finally the first steps were made to investigate the dynamics of single particle movement within the ER membrane. In the future this will be used to inform on how the structure of the ER may affect its function in the context protein dynamics within the different ER structural subdomains