Integrating chromatin structure and global chromosome dynamics
DNA associates with proteins to form chromatin which is essential for the compaction of the DNA into the cell nucleus and is highly dynamic in order to allow the different biological processes of the DNA to occur. Chromatin compaction is achieved at different hierarchical levels: the 10nm fibre (DNA associates to nucleosomes formed by different histones), the Higher Order Chromatin fibre and the 300 nm chromosome structures. This study has shown that both H1 and H4 histones play a crucial role in preserving meiotic as well as mitotic chromosome structure and functional genome integrity in Arabidopsis. The role of the different linker histone H1 isoforms as well as the core histone H4 in Arabidopsis thaliana was investigated using T-DNA and RNAi mutant lines which showed different meiotic defects. Chromosomal breaks as well as non-homologous connections in the h4RNAi were linked to 45S/5S rDNA disorganisation, suggesting that H4 preserves chromosome integrity at these rDNA regions. Ath1.1 mutant presented univalents and reduced chiasma frequency at metaphase I, linked to a severe defect in ASY1 localisation on the meiotic chromosome axes. Thus, indicating that histone H1.1 is vital for proper chromatin axis organization that permit normal loading of recombination machinery proteins in Arabidopsis.