From shaping organelles to signalling platforms: the emerging functions of plant ER–PM contact sites

The plant endoplasmic reticulum (ER) defines the biosynthetic site of lipids and proteins destined for secretion, but also contains important signal transduction and homeostasis components that regulate multiple hormonal and developmental responses. To achieve its various functions, the ER has a unique architecture, both reticulated and highly plastic, that facilitates the spatial-temporal segregation of biochemical reactions and the establishment of inter-organelle communication networks. At the cell cortex, the cortical ER (cER) anchors to and functionally couples with the PM through largely static structures known as ER–PM contact sites (EPCS). These spatially confined microdomains are emerging as critical regulators of the geometry of the cER network, and as highly specialized signalling hubs. In this review, we share recent insights into how EPCS regulate cER remodelling, and discuss the proposed roles for plant EPCS components in the integration of environmental and developmental signals at the cER–PM interface.