Centromere Satellite Repeats Have Undergone Rapid Changes in Polyploid Wheat Subgenomes

Area of Science:

• Genetics
• Molecular Biology
• Plant Science

Background:

• Centromeres are essential for homologous chromosome pairing during meiosis.
• Polyploid plants, like hexaploid bread wheat (Triticum aestivum), face challenges in differentiating homologs from homoeologs due to complex genomes.
• The sequence composition and evolutionary history of wheat centromeres remain largely uncharacterized.

Purpose of the Study:

• To map the centromeres of Triticum aestivum.
• To identify and characterize functional centromeric satellites and their role in meiosis.
• To investigate the evolutionary dynamics of centromere organization in wheat.

Main Methods:

• Chromatin immunoprecipitation sequencing (ChIP-seq) using antibodies against the centromeric histone H3 variant (CENH3).
• Phylogenetic analysis of satellite DNA sequences.
• Comparative analysis of centromere organization across different ploidy levels in wheat.

Main Results:

• Identified two types of functional centromeric satellites, abundant in two of the three T. aestivum subgenomes.
• Discovered that these satellites exhibit specific phased binding to CENH3 nucleosomes and have diverged across subgenomes.
• Observed a decrease in satellite signals and an increase in satellite variation from diploid to hexaploid wheat, with some centromeres lacking satellite repeats.
• Detected evolutionary rearrangements including local expansion, inversions, and gene expression changes in wheat centromeres.

Conclusions:

• Wheat centromeres exhibit subgenome asymmetry in their organization and satellite composition.
• Evolutionary changes in centromeric satellites and rearrangements contribute to centromere diversity in wheat.
• This asymmetry may play a critical role in ensuring proper homologous chromosome pairing during meiosis in polyploid wheat.