The size diversity of the Pteridaceae family chloroplast genome is caused by overlong intergenic spacers.

Background: While the size of chloroplast genomes (cpDNAs) is often influenced by the expansion and contraction of inverted repeat regions and the enrichment of repeats, it is the intergenic spacers (IGSs) that appear to play a pivotal role in determining the size of Pteridaceae cpDNAs. This provides an opportunity to delve into the evolution of chloroplast genomic structures of the Pteridaceae family. This study added five Pteridaceae species, comparing them with 36 published counterparts.

Results: Poor alignment in the non-coding regions of the Pteridaceae family was observed, and this was attributed to the widespread presence of overlong IGSs in Pteridaceae cpDNAs. These overlong IGSs were identified as a major factor influencing variations in cpDNA size. In comparison to non-expanded IGSs, overlong IGSs exhibited significantly higher GC content and were rich in repetitive sequences. Species divergence time estimations suggest that these overlong IGSs may have already existed during the early radiation of the Pteridaceae family.

Conclusions: This study reveals new insights into the genetic variation, evolutionary history, and dynamic changes in the cpDNA structure of the Pteridaceae family, providing a fundamental resource for further exploring its evolutionary research.