In Depth Topological Analysis of Arabidopsis Mid-SUN Proteins and Their Interaction with the Membrane-Bound Transcription Factor MaMYB

Mid-SUN proteins are a neglected family of conserved type III membrane proteins of ancient origin with representatives in plants, animals, and fungi. Previous higher plant studies have associated them with functions at the nuclear envelope and the endoplasmic reticulum (ER). In this study, high-resolution confocal light microscopy is used to explore the localisation of SUN3 and SUN4 in the perinuclear region, to explore topology, and to study the role of mid-SUNs on endoplasmic reticulum morphology. The role of SUN3 in the ER is reinforced by the identification of a protein interaction between SUN3 and the ER membrane-bound transcription factor maMYB. The results highlight the importance of mid-SUNs as functional components of the ER and outer nuclear membrane.

Automated summary

Mid-SUN proteins are a type III membrane protein family of ancient origin that have been overlooked, but are widely present in plants, animals, and fungi. Previous studies have shown their involvement in the nuclear envelope and endoplasmic reticulum (ER) functions in plants. This study used high-resolution confocal light microscopy to investigate the localization of SUN3 and SUN4 in the perinuclear region, explore their topology, and study their impact on ER morphology. The interaction between SUN3 and the ER membrane-bound transcription factor maMYB further supports the role of SUN3 in the ER. These findings highlight the importance of mid-SUNs as functional components of the ER and outer nuclear membrane.