Extrachromosomal Circular DNA: A Dynamic Regulator of Genome Plasticity and Adaptation in Plants.

Extrachromosomal circular DNA (eccDNA) is an emerging class of mobile genetic elements that exist independently of linear chromosomes. Initially recognized for its role in cancer pathogenesis, eccDNA is now gaining traction in plant genomics as a potent driver of genome plasticity. In this Review, we summarize the latest research findings on eccDNA biology, focusing on its biogenesis, detection methodologies, and functional mechanisms. In addition, we propose a unifying concept of eccDNA as a dynamic "adaptive genomic regulator" in plants, instrumental in mediating gene dosage amplification, epigenetic reprogramming, and horizontal DNA transfer. Finally, we outline key unanswered questions and technical bottlenecks that must be addressed to translate eccDNA research into crop improvement strategies and sustainable agriculture. By framing eccDNA as an active regulatory entity rather than a passive genomic byproduct, this Review aims to catalyze research into this fascinating molecular class and its potential applications in plant biotechnology.