Endoplasmic reticulum homeostasis in plant-pathogen interaction: new scenarios for an old story.

The endoplasmic reticulum (ER) is a specialized organelle that connects almost all subcellular structures from the plasma membrane to the nucleus. The ER is involved in secretory protein synthesis, folding and processing. Evidence has emerged that the ER is at the frontier of the battle between plant hosts and pathogens. Its structural and functional homeostasis is crucial for the fate of plant cell survival. Pathogens secrete effectors to take over normal functions of ER, while host plants fight back to activate ER stress responses. Exciting achievements have been made in the studies in the host plant-pathogen dynamics during the past decades. Namely, some new players involved have been recently resolved from both pathogens and hosts. In this review, we will summarize advances in identifying structural characteristics of the key pathways and effectors targeting the ER. Newly identified ER-phagy receptors and components downstream of inositol requiring 1 (IRE1) will be described. And future studies will be envisaged to further our understanding of the missing parts in this dynamic frontier.