LITTLE NUCLEIGenes Affecting Nuclear Morphology inArabidopsis thaliana

Abstract

Efforts to understand nuclear organization in plant cells have received little assistance from the better-studied animal nuclei, because plant proteomes do not contain recognizable counterparts to the key animal proteins involved in nuclear organization, such as lamin nuclear intermediate filament proteins. Previous studies identified a plant-specific insoluble nuclear protein in carrot (Daucus carota), called Nuclear Matrix Constituent Protein1 (NMCP1), which contains extensive coiled-coil domains and localizes to the nuclear periphery. Here, we describe a genetic characterization of two NMCP1-related nuclear proteins in Arabidopsis thaliana, LITTLE NUCLEI1 (LINC1) and LINC2. Disruption of either gene caused a reduction in nuclear size and altered nuclear morphology. Moreover, combining linc1 and linc2 mutations had an additive effect on nuclear size and morphology but a synergistic effect on chromocenter number (reduction) and whole-plant morphology (dwarfing). The reduction in nuclear size in the linc1 linc2 double mutant was not accompanied by a corresponding change in endopolyploidy. Rather, the density of DNA packaging at all endopolyploid levels in the linc1 linc2 mutants was increased significantly. Our results indicate that the LINC coiled-coil proteins are important determinants of plant nuclear structure.

How plants LINC the SUN to KASH

“…They are conserved in many plant species and contain long coiled-coil domains similar to lamins, though at almost twice the size, and NMCP1 and CRWN1 are located at the nuclear periphery. 68,69 In addition to the nuclear shape change, the crwn1-1 crwn2-1 double mutant has a significantly reduced nuclear volume, fewer chromocenters, and a dwarf plant phenotype. 68 Nuclear shape change caused by mutations in lamin genes was observed in a series of human diseases called laminopathies.…”

“…68,69 In addition to the nuclear shape change, the crwn1-1 crwn2-1 double mutant has a significantly reduced nuclear volume, fewer chromocenters, and a dwarf plant phenotype. 68 Nuclear shape change caused by mutations in lamin genes was observed in a series of human diseases called laminopathies. 70 One such disease is Hutchinson-Gilford progeria syndrome (HGPS), which is linked to point mutations in the human lamin A gene (Lmna).…”

“…68 Plant genomes do not encode homologs of animal lamin genes. The Daucus carota L. (carrot) nuclear matrix constituent protein 1 (NMCP1) and its Arabidopsis homologs-CRWN1, CRWN2, CRWN3 and CRWN4-have been proposed as putative plant counterparts of animal lamins.…”

Dynamics of the Plant Nuclear Envelope and Nuclear Pore

“…1A). Mutants in two NMCP1-related proteins in Arabidopsis (Arabidopsis thaliana), LITTLE NUCLEI1 (LINC1) and LINC2, have reduced nuclear size and changes in nuclear morphology, suggesting an involvement in plant nuclear organization (Dittmer et al, 2007).…”

“…There are now a significant number of proteins available to serve as markers for NE dynamics in plants: NMCP1/2 (LINC1/2), SUN1/2, WPP DOMAIN-INTERACTING PROTEIN1 (WIP1)/2/3, WPP DOMAIN-INTERACTING TAIL-ANCHORED PROTEIN1 (WIT1)/2, and Nuclear Pore Anchor (NUA; Dittmer et al, 2007;Jacob et al, 2007;Xu et al, 2007aXu et al, , 2007bZhao et al, 2008;Graumann et al, 2010;Fig. 1A).…”