ER-to-Golgi trafficking through a dynamic intermediate cis-Golgi tubular network in Arabidopsis.

Endoplasmic reticulum (ER)-to-Golgi trafficking is a central process of the secretory system of eukaryotic cells that ensures proper spatiotemporal sorting of proteins and lipids. However, the nature of the ER-Golgi intermediate compartments (ERGICs) and the molecular mechanisms mediating the transition between ERGICs and the Golgi, as well as the universality of these processes among eukaryotes, remain undiscovered. Here we identify a reticulated tubulo-vesicular network, labelled by MEMBRIN proteins, that is mostly independent of the Golgi, highly dynamic at the ER-Golgi interface and crossed by ER-induced released luminal cargos. We find that plant ERGICs become stabilized by the interaction they establish with pre-existing Golgi and gradually mature into Golgi cisternae, this process being dependent on C24-ceramide sphingolipids. Our study is a major twist in the understanding of the Golgi, as it identifies that the ERGICs in plants comprise a Golgi-independent and highly dynamic tubular network from which arise more stable Golgi-associated pre-cisternae structures.