Overall, chromosome dynamics in interphase nuclei is still quite poorly understood. the area within the nucleus to which movement of a chromosome segment is constrained (Kato and Lam, 2003). Interestingly, endoreduplication-driven poly- ploidy has been found to reduce chromosome movement speed but increase the freedom of movement, i.e. Interstitial chromosome regions generally exhibit more movements than centromeres.

However, so far, it appears that interphase chromosomes only display mostly limited, diffusive movements (Kato and Lam, 2003 Fang and Spector, 2005). In the past few years new tools have been developed to facilitate investigations of interphase chromosome dynamics in live cells in Arabidopsis (Fang and Spector, 2005 Matzke et al., 2005, 2008, 2010). These data will be a starting point for understanding how interphase chromosome arrangement affects gene expression. We anticipate that the near future will bring a more complete picture of interphase chromosome arrangement and dynamics during growth and development as well as under various environmental conditions in plants. However, it is unclear if there are particular nucleus regions that are occupied by highly expressed genes. In Arabidopsis, the majority of genes are located on euchromatic loops stretching out of the chromocenters (Fransz et al., 2002). Effects of chromatin organization on gene expression are poorly understood in plants. It has been proposed that physical interactions between gene copies located on different chromosomes may contribute to gene silencing (Lancto ˆt et al., 2007). On the other hand, there might be also heterochromatic neighborhoods in which gene expression is silenced. Hundreds of such factories are proposed to be present in each nucleus and they are thought to be anchored to a nuclear substructure. This notion has lead to development of the concept of transcriptional factories, discrete sites in the nucleus where gene transcription is particularly active (Sutherland and Bickmore, 2009). Arrangement of chromosome territories that brings certain chromosome regions together has the potential to contribute to regulation of gene expression. In the past few years, there has been a growing interest in understanding how chromosome and chromatin arrangement in interphase nuclei affect gene activity. In rice, heat stress has been shown to induce chromatin decondensation (Santos et al., 2011). the light inten- sity of their original habitats (Tessadori et al., 2009).

Diagram of prophase