The nuclear organelle is the defining feature of eukaryotic organisms. Besides harboring the genome, the nucleus separates fundamental nuclear activities occurring in the nucleoplasm, including gene regulation, DNA repair, and RNA processing, from the cytoplasm. The nucleus also shows a high degree of internal spatial organization and it is becoming increasing clear that knowledge of nuclear organization is vital for a comprehensive understanding of diverse nuclear processes.

Certain cell types are correlated with specific nuclear shapes and nuclear volumes. Routine nuclear morphological differentiation is tied to cell specialization and is thought to be an integral component of developmental gene expression programs. In plants a wide array of nuclear morphologies are present within a single tissue, and in certain cell types nuclei migrate bi-directionally throughout the cell. However, very little is known about the molecular determinants of nuclear morphology, organization and dynamics in plants.

The Arabidopsis LINC (LITTLE NUCLEI) genes encode a novel family of plant-specific coiled-coil proteins that are important determinants of nuclear morphology and organization. A loss-of-function genetic analysis of the LINC genes has revealed that certain higher-order linc mutants, e.g., linc1-1 linc2-1, linc1-1 linc3-1, and lincl-1 linc3-1 linc4-1 exhibit a range of whole-plant morphological phenotypes. linc1-1 and linc2-1 mutations also cause nuclear abnormalities, including reduced nuclear size, altered nuclear shape, and decreased numbers of heterochromatin-rich chromocenters. In addition, the LINC proteins influence the coupling of nuclear DNA content with nuclear volume, as shown by an increase in nuclear DNA density in the linc1-1 linc2-1 double mutant. Analysis of LINC1 and LINC2 gene expression patterns reveals strong expression within proliferating tissues, suggesting the LINC proteins function at an early stage in nuclear development. All LINC proteins examined localize to the nucleus; however, individual LINC proteins maintain unique sub-nuclear localizations reflecting a range of possible nuclear functions. Furthermore, the linc1 mutation was utilized to address the causal relationship between nuclear migration and differentiation. Despite a block in nuclear shape differentiation, linc1 mutant nuclei still migrate normally. The results described here provide some of the first steps toward a more complete understanding of nuclear morphology and organization in plants.