Mitochondrial genome architecture and evolutionary characteristics of cliff-endemic Opisthopappus in Asteraceae

Abstract

Opisthopappus is a perennial herb endemic to cliff habitats of the Taihang Mountains and represents a wild germplasm resource for stress-resistance research on Asteraceae industrial crops. However, its mitochondrial genomic architecture and evolutionary patterns remain largely unexplored. Here, the complete mitochondrial genomes of Opisthopappus taihangensis (Y. Ling) C. Shih (223,085 bp) and Opisthopappus longilobus C. Shih (209,744 bp) were assembled via a hybrid-sequencing strategy to explore mitogenomic evolutionary dynamics of the two congeneric species. Both mitogenomes were assembled as circular-mapping configurations and share conserved pseudogenes ( rpl16 , rps1 , rps19 ) and four copies of trnM-CAT , but differ by an ~8.3 kb inversion encompassing nad7 and ccmFn . Notably, rps12 is pseudogenized in O. taihangensis but remains intact in O. longilobus . A 378-bp nuclear sequence exhibiting 100% identity to mitochondrial rps12 was recovered in O. taihangensis , indicating a candidate nuclear mitochondrial DNA segment. Codon usage analyses revealed a clear preference for A/U-ending codons in both species, and suggest that codon bias is influenced by multiple evolutionary factors beyond mutational pressure. Branch-site model tests identified a significant signature of positive selection in nad5 (encoding a core subunit of respiratory complex I). Predicted RNA-editing sites (456 in O. taihangensis , 463 in O. longilobus ) are predominantly associated with hydrophilic-to-hydrophobic amino-acid substitutions. Transcriptome quantification under salt stress revealed stress-responsive expression profiles for mitochondrial genes, with interspecific expression divergence observed. Our study generates comparative mitogenomic resources and identifies candidate stress-associated loci (e.g., nad5 from selection analysis; atp1 , cox1 from expression trends), providing a foundation for subsequent functional assays and stress-adaptation research in Asteraceae.