Characterisation of the Arabidopsis mid-SUN proteins at the plant NE

The Sad1-Unc84 (SUN) proteins of Arabidopsis thaliana (Arabidopsis) consist of two sub-groups - the classical C-terminal (Cter) SUN domain proteins and the mid-SUN domain proteins. The mid-SUN domain proteins have been suggested to have a functional role in Linker of Nucleoskeleton and Cytoskeleton (LINC) complex formation at the nuclear envelope (NE), similarly to Cter-SUN domain proteins. In addition to interacting with LINC complex components, they have been reported to localise to both the NE and endoplasmic reticulum (ER). There is also evidence that they interact with the ER membrane transcription factor AtmaMyb based on results from membrane yeast two hybrid (MY2H) screens. This project aimed to further characterise the Arabidopsis mid-SUN proteins AtSUN3 and AtSUN4 and their function at the plant ER and NE. Putative interactions between SUN domain proteins and AtmaMyb were tested using acceptor photobleaching Förster resonance energy transfer (apFRET). Interactions were detected between AtSUN3 and AtmaMyb exclusively. Experiments using AtSUN3 domain deletions indicated that the coiled coil domain of AtSUN3 is required for homomeric interactions. FRET measured by fluorescence lifetime microscopy (FRET-FLIM) was also used to investigate mid-SUN homo- and heterodimerisation. ER-enrichment of AtSUN3 and AtSUN4 was confirmed by calculating the ratio of fluorescence intensity between ER and nuclear periphery. Additionally, a high-resolution confocal imaging technique used to determine protein localisation at the nuclear periphery was further refined. This was used to show that fluorescent protein fusions of both mid-SUN proteins co-localised with the ER/outer nuclear membrane (ONM) marker mCherry and not the inner nuclear membrane (INM) membrane marker AtSUN2. These results indicate that AtSUN3 and AtSUN4 localise to the ONM/perinuclear ER and not to the INM. Altogether, this work indicates that mid-SUNs have functional roles in addition to LINC complex formation based on protein-protein interactions they form due to their sub-cellular localisation.

Grantor dc:publisher

Oxford Brookes University

Year dc:date

2021

Author dc:creator

• Andov, Bisa

Contributors dc:contributor

• Graumann, Katja
• Kriechbaumer, Verena
• Evans, David. E

Statement dc:rights

• All rights reserved

Language dc:language

en

DOI dc:identifier

https://doi.org/10.24384/pzvs-w503

OAI identifier oai:identifier

tle:c53312ea-7af1-4a87-b8eb-b40db739d7b9:d6bd9758-527a-46cd-bfe2-c433766e8fca:1