Comparative analysis of mitochondrial genome of Gaultheria (Ericaceae) provides insights into their adaptation to high elevation.

backgroundGaultheria is one of the most valuable medicinal species and exhibits contrasting adaptability to various habitats and elevations. However, the scarcity of genomic research, with only a draft nuclear genome and a few complete plastomes available, significantly limits our understanding of its evolutionary characteristics from a mitochondrial perspective and hinders further research into comparative genomics. To elucidate the structural characteristics, variations, and adaptive evolution of the organelle genomes of this genus, we first assembled and compared the mitochondrial genomes of two representative species, namely, G. prostrata (Gpr), which is distributed at high elevations (3700 to 4800 m), and G. crenulata (Gcr), which is distributed at relatively lower elevations (200 to 2900 m), with 16 known mitochondrial genomes from the Ericales.

resultsThis study newly sequenced and assembled the mitogenome of Gpr and Gcr, and plastome of Gpr. The genome sizes and GC contents of the Gpr and Gcr mitochondrial genomes, as well as the Gpr chloroplast genome, are as follows: 703,983 bp and 45.20%, 831,994 bp and 45.35%, and 192,038 bp and 36.61%, respectively. In total, 41 and 40 protein-coding genes (PCGs) and 27 and 29 tRNAs are annotated for Gpr and Gcr mitogenome, respectively, while the two mitogenomes contain one complete circular molecule with three rRNAs and abundant RNA editing sites. The mitogenome of Gpr can recombine into various configurations, which are likely mediated by two repeat pairs (R1 and R2). In Gpr, 15 genes (8 PCGs and 7 tRNA genes) were identified in migrated fragments from the plastome to the mitogenome. In Gcr, an additional 8 genes (7 PCGs and 1 tRNA gene) were found migrated, with ycf2, rrn4.5, and trnI-GAU absent. Phylogeny and collinearity indicated that the relationship between Gpr and Gcr are closest. Compare to Gcr, the ccmC gene of Gpr has more RNA edits and undergoes potentially positive selection (Ka/Ks > 1). Furthermore, compared to Gcr at lower elevations, Gpr contains an extra copy of the cytb gene with an RNA editing-mediated start codon, an additional atp9 gene with an RNA editing-mediated stop codon, and one more copy of sdh3.

conclusionsWe provided a high-quality and well-annotated mitogenome for two species of Gaultheria, and demonstrated the presence of diverse configurations. Our results reveal the potential adaptation mechanisms of Gpr to high-elevation extremes environmental and provide valuable resources for further understanding the evolutionary pattern of organelle genomes in Ericales.