Plant SUN domain proteins: components of putative plant LINC complexes?

Abstract

We have recently reported the identification and characterization of Sad1/UNC84 (SUN) domain proteins in various plant species. In animals and yeasts, SUN domain proteins are localized at the inner nuclear membrane and form a bridge across the nuclear envelope (NE) by interacting with outer nuclear membrane-localized Klarsicht/Anc-1/Syne-1 homology (KASH) domain proteins. This bridge physically connects cytoskeletal elements with chromatin and nucleoskeletal components. These multiprotein complexes are essential for various cellular and nuclear processes. The identification of SUN domain proteins provides the first evidence of putative NE bridging complexes in plants. Here we speculate on the composition and functions of these in regards to our current understanding of plant SUN domain proteins.

Figure 1

The LINC complex in animal and yeast systems (A) connects nuclear and cytoskeletal components across the NE. The outer nuclear membrane (ONM ) contains Klarsicht/ANC -1/SYNE -1 homology (KASH) domain proteins, which link actin, microtubule (MT ) associated elements such as dynamin, kinesin and centrosomes to the NE . The inner nuclear membrane (INM ) associated Sad1/UNC −84 (SUN ) domain proteins anchor chromatin, telomeres and lamins to the nuclear face of the NE . SUN and KASH domain proteins interact with each other in the periplasm completing the linkage. In plants (B), cytoskeletal and nuclear components are also associated with the NE—MT and actin elements on the cytoplasmic face, chromatin and filamentous lamin-like elements on the nuclear side. The nature of their NE anchorage remains unknown but the identification of plant SUN domain proteins suggests the presence of putative plant LINC complexes. Their structure and functions, however, may differ to those in animal and yeast systems.