The plant endoplasmic reticulum (ER), a highly dynamic membrane-bound organelle, is not only the site of secretory protein production and lipid synthesis, but also responsible for calcium storage. It is currently hypothesised that the shape of the ER network relates to these functions. The sheets, large at areas of network are proposed to be the sites of protein production and the tubules, thin, highly-mobile and interconnected, the regions of lipid production and calcium storage. The reticulon protein family has been shown to bend the ER lipid bilayer to form tubules and the edges of sheets. Identifying protein interactors to reticulons may help to understand how the morphology of the ER is controlled or in uenced. Mass spectrometry and co-immunoprecipitation techniques were used to identify protein interactors to the Arabidopsis thaliana seed-specific reticulon, RTN13. Five non-reticulon proteins were found to interact with RTN13 in developing A. thaliana seed; GTP-binding protein 2, lysophospholipase 1, NADH: Cytochrome B5 Reductase 1, sterol methyltransferase 2 and synaptotagmin a. Microscopy analysis of the ER in over-expression lines and T-DNA insertions lines for each putative interactor, showed that only sterol methyltransferase 2 and synaptotagmin a influenced the ER morphology. Additionally, the morphology of the ER was analysed during seed development and germination through confocal microscopy. An image analysis macro was used to determine the percentage of sheet morphology in the network. Significant changes in the amount of sheet morphology were recorded in the ER of cotyledon cells during seed development and over the first six days of germination. Wild type embryos were also compared to mutants known to have altered ER morphology. The analysis suggested that the amount of sheet morphology is maximal at times of maximum protein production, highlighting the link between ER form and function.