Holokinetic centromeres and efficient telomere healing enable rapid karyotype evolution

Area of Science:

• Genetics
• Molecular Biology
• Plant Science

Background:

• Species with holocentric chromosomes exhibit rapid karyotype evolution.
• Unlike monocentric chromosomes, holocentric chromosome fragments retain centromere activity after breakage.
• This unique characteristic suggests a mechanism for accelerated evolution via chromosome fragmentation.

Purpose of the Study:

• To investigate the mechanisms underlying rapid karyotype evolution in holocentric species.
• To analyze chromosome complements of irradiated Luzula elegans plants to understand breakage and healing processes.
• To determine if chromosome fragments in holocentric species are stable and transmissible.

Main Methods:

• Irradiation of Luzula elegans plants to induce chromosome breakage.
• Analysis of chromosome complements using fluorescent in situ hybridization (FISH) for centromere markers (CENH3, histone H2AThr120ph).
• Microscopic observation to assess mitotic mobility of fragmented chromosomes and telomere synthesis at break points.
• Tracking of telomerase activity and transmission of chromosome fragments across generations.

Main Results:

• Irradiated chromosomes in Luzula elegans produced fragments with holocentromere-typical signals (CENH3, histone H2AThr120ph).
• These fragments exhibited normal mitotic mobility, similar to unfragmented chromosomes.
• Newly synthesized telomeres were detected at break points within 3 weeks, indicating active telomere healing.
• Telomerase activity was confirmed, suggesting a telomerase-based chromosome healing mechanism.
• Most offspring from irradiated plants successfully transmitted the holocentric chromosome fragments.

Conclusions:

• Holocentric chromosome activity and rapid telomere formation at break points enable accelerated karyotype evolution.
• Chromosome fissions and rearrangements are facilitated by the stability and transmissibility of holocentric fragments.
• This mechanism provides a significant evolutionary advantage for species with holocentric chromosomes, allowing for rapid adaptation and diversification.