Dynamic Histone Phosphorylation Changes for Maize Chromosome Orientation and Segregation

Genomic stability is very important for all organisms. It requires a precise cell division with proper orientation and successful segregation of chromosomes in both mitosis and meiosis. Histone modifications can preclude or attract factors that are associated with various functional chromatin organizations. Dynamic histone phosphorylations during cell division are very important for chromosome orientation and segregation.

Here, we firstidentified two histone phosphorylation sites at H2AT133 and H3T3 in maize and clonedthe conserved kinases Bub1 and Haspin that catalyze these modifications. Phosphorylation of histone H2A at T133 is specific to centromere regions and associated with centromere activity. H2A phosphorylation is coincident with the signals of kinase Bub1 during meiosis. The H2AT133ph signals reduced in somatic cells of bub1 RNAi transgenic lines, but there were no changes in meiocytes. ChIP-seq distribution patterns in centromeres were in substantial agreement with anti-CENH3 and anti-H2AT133ph, suggesting that the CENH3 nucleosome has a conserved organization with histone H2AT133 phosphorylation. The signals of Haspin-dependent H3T3 phosphorylation are distributed along the entire sister chromatids in prophase and are restricted to the inner parts of functional centromeres in metaphase. The functional centromere contains a mixture of H3 and CENH3 nucleosomes and changes organization at metaphase. In maize meiocytes, H3T3 phosphorylation extends to the entire chromosome in metaphase I, but it is only observed in the centromere in metaphase II. We also observed Haspin signals along the entire chromosome in pachytene.

These results suggest that a series of specific dynamic phosphorylations of core histones within the centromere regions distinguish different centromeric organizations during cell division, which may be vital for successful chromosome segregation.