Chloroplast genomics of Campanula americana

Plastids genomes are typically highly conserved genomes in most land plants. However, plastid genomes in the Campanulaceae family exhibit high rates of substitution and structural rearrangements, although intraspecific structural variation has not been documented. In this study, we assembled and analyzed the chloroplast genomes of three distinct lineages of Campanula americana, the Appalachian (A), Eastern (E), and Western (W) lineages. Previous research has shown that offspring from interlineage crosses exhibit cytonuclear incompatibility manifested as albino or chlorotic phenotypes, suggesting that the plastid genome plays a role in this phenomenon. We investigate the structural variation and repetitive DNA content among these lineages and compare the repetitive DNA content with that of other species within the family. Our findings suggest a strong correlation between genome size and repetitive DNA content, with C. americana exhibiting one of the largest and most repetitive plastid genomes within Campanulaceae. This study provides the first evidence of large intraspecific structural variation in a plastid genome, highlighting the role of structural and sequence divergence in plastid genome evolution and potentially in the plastid-nuclear incompatibility within C. americana.