Mitochondrial genome analysis of the endangered Oreocharis esquirolii: insights into evolutionary adaptation and conservation.

backgroundOreocharis esquirolii H. Lév., a member of the Gesneriaceae family with an actinomorphic corolla, is evaluated as vulnerable and classified as a National Grade I Protected Plant. The species is endemic to Guizhou Province in southwestern China, restricted to the Longtoudashan Nature Reserve. Current research on mitochondrial genomes (mitogenomes) in Gesneriaceae plants is limited to only three species. Given the crucial role of mitochondria in plant energy metabolism and stress responses, mitogenome analyses may offer novel insights into the genetic basis of adaptive traits and contribute to understanding evolutionary processes. Therefore, in this study, we assembled and annotated the mitogenome of O. esquirolii, and performed comparative analyses to investigate structural features and variation across mitogenomes.

resultsThe mitogenome of O. esquirolii exhibited a linear structure, consisting of 36 protein-coding genes (PCGs), 23 tRNA genes, three rRNA genes, and one pseudogene. A total of 158 repeat sequences were identified, with the majority located in intergenic regions, while a smaller fraction appeared in coding regions. Homology analysis revealed 58 plastid-derived fragments, spanning 52,103 bp and accounting for 11.45% of the mitogenome. Collinearity analysis demonstrated extensive genomic rearrangements between O. esquirolii and its close relatives, implying structural divergence during evolution. Positive selection signals were detected in seven coding genes of the O. esquirolii mitogenome, with a potential impact on environmental adaptation. Phylogenetic analysis inferred from shared mitochondrial genes presented a well-supported topology, in which O. esquirolii was closely related with Primulina hunanensis K. M. Liu & X. Z. Cai.

conclusionOverall, this study presents the first report of the complete mitogenome of O esquirolii, revealing a linear structure, extensive genomic rearrangements, and frequent plastid-derived DNA insertions. Despite structural variation, the mitogenomes of O. esquirolii remains relatively conserved at the sequence level, particularly in terms of gene content, GC content, and codon usage bias. These findings highlight dynamic genomic evolution and provide critical molecular resources for future studies on plant adaptation and species conservation.