Distinct evolutionary trajectories of subgenomic centromeres in polyploid wheat

Area of Science:

• Genomics
• Evolutionary Biology
• Molecular Biology

Background:

• Centromeres are vital for chromosome segregation and genome stability.
• Centromere evolution in polyploids, like wheat, is complex and not well understood.
• Wheat's polyploid history makes it an ideal model for studying centromere evolution.

Purpose of the Study:

• To systematically compare centromeres in common wheat and its ancestors.
• To elucidate the evolutionary trajectories of centromeres in different wheat subgenomes.
• To understand the role of retrotransposon invasions in centromere evolution.

Main Methods:

• Comparative analysis of reference genome assemblies.
• Utilizing CENH3-Chromatin Immunoprecipitation (ChIP) data across ploidy levels.
• Integration of einkorn centromere assemblies and Aegilops tauschii pan-genomes.

Main Results:

• Wheat centromeres are primarily composed of five types of centromeric-specific retrotransposon elements (CRWs), with CRW1 and CRW2 being most common.
• Distinct evolutionary paths for AA and DD subgenome centromeres were identified, showing variations in copy number, age, and CRW composition.
• CRW invasions shaped AA subgenome centromere evolution, while DD subgenome centromere expansion occurred gradually from diploid to hexaploid stages.

Conclusions:

• Centromere adaptation, evolution, and maturation in polyploid wheat are comprehensively detailed.
• Retrotransposon invasions are key drivers of centromere evolution in polyploid wheat.
• DD subgenome centromere expansion is a slow, adaptive process, not an immediate response to polyploidization.