A nuclear localization signal targets tail-anchored membrane proteins to the inner nuclear envelope in plants

Abstract

Protein targeting to the inner nuclear membrane (INM) is one of the least understood protein targeting pathways. INM proteins are important for chromatin organization, nuclear morphology and movement, meiosis, and have been implicated in human diseases. In opisthokonts, one mechanism is transport-factor mediated trafficking, in which nuclear localization signals (NLSs) function in nuclear import of transmembrane proteins. To explore if this pathway exists in plants, we fused the SV40 NLS to a plant ER tail-anchored protein and showed that the GFP-tagged fusion protein was significantly enriched at the NE of leaf epidermal cells. Airyscan sub-diffraction limited confocal microscopy showed that it displays localization consistent with an INM protein. Nine different monopartite and bipartite NLSs from plants and opisthokonts, fused to a chimeric tail-anchored membrane protein, were all sufficient for NE enrichment and both monopartite or bipartite NLSs were sufficient for trafficking to the INM. Tolerance for different linker lengths and protein conformations suggests that INM trafficking rules might differ from those in opisthokonts. The INM proteins developed here can be used to target new functionalities to the plant nuclear periphery.