Abstract
The mechanisms underlying the emergence of new DNA repeat classes remain poorly understood. One such example is the formation of interstitial telomeric repeat (ITR) domains commonly viewed as telomere-fossil byproducts of chromosome rearrangements. Here, we report that in Arabidopsis thaliana , ITRs arise from centromeres as centromeric-telomeric mosaic satellites that expand into higher-order structures via in situ amplification. Long-read sequencing of mutation accumulation lines and forward simulations of mutational processes confirmed the propensity of centromeres to form telomeric motifs. During establishment, ITRs adopt an atypical chromatin state that excludes CENH3 incorporation, thereby enabling escape from the functional constraints of centromere identity. Accordingly, a pangenomic survey of natural accessions showed that ITRs vary abruptly and independently of telomere length, notably through transposon-associated block duplications. These findings identify centromeres as major sources of telomeric sequences and an original route for the emergence of new DNA satellite types.
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Abstract
The mechanisms underlying the emergence of new DNA repeat families remain poorly understood. Interstitial telomeric repeat (ITR) domains compose a class of repetitive elements associated with genomic instability and disease that illustrates this knowledge gap. Commonly viewed as telomere-fossil byproducts of chromosome rearrangements, their origins and evolutionary dynamics have long been obscured by their highly repetitive nature. Here, combining a pangenomic survey of Arabidopsis thaliana with forward simulations of centromere evolution, we show that megabase-scale ITR domains arise in situ from canonical centromeric repeat arrays. Mutation-driven gains of telomeric motifs within centromeric satellites produce centromeric-telomeric mosaic satellites, which expand into higher-order structures via head-to-tail amplification. Despite their proximity and sequence similarity to centromeres, ITR satellites adopt an atypical chromatin state that excludes CENH3 incorporation, enabling escape from the functional constraints of centromere identity. Accordingly, ITR abundance varies abruptly among natural accessions, independently of telomere length, population relatedness or environmental variables, often via transposon-associated block duplications. Collectively, this study identifies centromeres as an unrecognized source of telomeric sequences and reveals an unexpected route shaping the rise of new satellite types.
Competing Interest Statement
The authors have declared no competing interest.
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