Condensation patterns of prophase/prometaphase chromosome are correlated with H4K5 histone acetylation and genomic DNA contents in plants.

Mitotic prophase chromosome condensation plays an essential role in nuclear division being therefore regulated by highly conserved mechanisms. However, degrees of chromatin condensation in prophase-prometaphase cells may vary along the chromosomes resulting in specific condensation patterns. We examined different condensation patterns (CPs) of prophase and prometaphase chromosomes and investigated their relationship with genome size and distribution of histone H4 acetylated at lysine 5 (H4K5ac) in 17 plant species. Our results showed that most species with small genomes (2C < 5 pg) (Arachis pusilla, Bixa orellana, Costus spiralis, Eleutherine bulbosa, Indigofera campestris, Phaseolus lunatus, P. vulgaris, Poncirus trifoliata, and Solanum lycopersicum) displayed prophase chromosomes with late condensing terminal regions that were highly enriched in H4K5ac, and early condensing regions with apparently non-acetylated proximal chromatin. The species with large genomes (Allium cepa, Callisia repens, Araucaria angustifolia and Nothoscordum pulchellum) displayed uniformly condensed and acetylated prophase/prometaphase chromosomes. Three species with small genomes (Eleocharis geniculata, Rhynchospora pubera, and R. tenuis) displayed CP and H4K5ac labeling patterns similar to species with large genomes, whereas a forth species (Emilia sonchifolia) exhibited a gradual chromosome labeling, being more acetylated in the terminal regions and less acetylated in the proximal ones. The nucleolus organizer chromatin was the only chromosomal region that in prometaphase or metaphase could be hyperacetylated, hypoacetylated or non-acetylated, depending on the species. Our data indicate that the CP of a plant chromosome complement is influenced but not exclusively determined by nuclear and chromosomal DNA contents, whereas the CP of individual chromosomes is clearly correlated with H4K5ac distribution.