Extrachromosomal Circular DNA are Functional, Heritable Units that Expand Genomic Plasticity and Confer Resilience

Extrachromosomal circular DNA (eccDNA) is a pervasive and dynamic component of eukaryotic genomes. eccDNA are nuclear-localised, double-stranded DNA circles that exist independently of the main chromatin body. They share many sequence features with chromosomal DNA; however, unlike chromosomes, eccDNAs are highly heterogenous, encode functional genes, are capable of autonomous replication and ultra-high gene expression, and do not necessarily segregate evenly or follow Mendelian inheritance during cell division. Although several recent reviews have focused on their roles in human health, emerging research in plants shows that eccDNAs are intricately associated with rapid adaptation to stress, particularly in weedy and invasive plants. This plant-centric review synthesizes evidence that eccDNAs carry full-length genes, regulatory elements, and transposable sequences, that enable gene amplification, novel protein variants, and context-specific expression. We propose that eccDNAs function as “genomic shock absorbers”: stress-inducible, non-Mendelian reservoirs of genetic diversity that buffer genomes against environmental challenges such as nutrient limitation and xenobiotic exposure. Drawing parallels with bacterial plasmids, we argue that eccDNA enable new forms of genome–environment interaction beyond those mediated by chromosomes. Harnessing these elements as non-Mendelian vehicles for genetic innovation could transform weed-derived resilience strategies into new routes for crop improvement, enabling the design of climate-ready, stress-resilient agriculture grounded in weed inspired mechanisms of adaptability and tolerance.