Plant LINC Complex at a Glance - Pages 15-25
A crucial structure in eukaryotic cells is the nuclear envelope (NE) which protects nuclear content and separates it from the cytoplasm. It consists of several main structures: the inner nuclear membrane (INM), the outer nuclear membrane (ONM) and the pore membrane connecting the INM and ONM. The ONM is associated with the rough endoplasmic reticulum (ER) at the perinuclear space (PNS) and executes many functions together with the ER. A number of membrane proteins anchor to the INM. They are linked to chromatin and the lamina: a meshwork composed of intermediate filament proteins and membrane associated proteins, which functions in attaching chromosomes to the NE and stabilizing nuclear structure. Anchored to the pore membrane are the nuclear pore complexes (NPC), which facilitate the exchange of macromolecules and proteins between cytoplasm and nucleus. A series of NE proteins have been identified in animal and yeast cells. Most of them are INM proteins, including Sad1/Unc-84 (SUN) domain proteins. ONM-specific proteins include Klarischt/ANC-1/SYNE homology (KASH) domain proteins. The SUN domain proteins and the KASH domain proteins form a bridge across the NE to connect cytoskeletal and nuclear components. In animal and yeast cells, SUN domain proteins associate with the lamins and nuclear actin. KASH domain proteins link to cytoskeletal components like actin, dynein and microtubules. The complex formed by the interacting SUN domain proteins and KASH domain proteins is called the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex. It provides a physical signalling pathway from the cellular membrane to the nucleus and is involved in various cell functions including positioning and movement of the nucleus during cell division. The discovery of plant SUN domain proteins indicates a putative LINC complex in plants. The Arabidopsis SUN domain proteins AtSUN1 and AtSUN2 have been identified as the homologues of animal and yeast SUN domain proteins in terms of sequences, structural features and function. In plants, however, no sequence homologues of KASH domain proteins have been identified. One assumption is that there are some proteins, which do not share homologous DNA sequences to KASH domain proteins, but are similar to KASH domain proteins in terms of protein structure and function.
Keywords: LINC, SUN Domain, KASH, Nucleus, Cytoskeleton.