# The Whole Mitochondrial Genome Sequence of Dendrobium loddigesii Rolfe, an Endangered Orchid Species in China, Reveals a Complex Multi-Chromosome Structure

## TL;DR

This study sequenced the mitochondrial genome of an endangered orchid, revealing a complex multi-chromosome structure with implications for orchid genome research.

## Contribution

The first complete mitochondrial genome assembly of Dendrobium loddigesii, revealing its multi-chromosome structure and RNA-editing features.

## Key findings

- The mitogenome consists of 17 circular subgenomes and contains 70 genes, including 36 protein-coding genes.
- The study identified 482 RNA-editing sites and 27 homologous fragments between the mitogenome and chloroplast genome.
- Phylogenetic analysis showed D. loddigesii and D. Amplum form a single clade with full bootstrap support.

## Abstract

Dendrobium loddigesii is a precious traditional Chinese medicine with high medicinal and ornamental value. However, the characterization of its mitochondrial genome is still pending. Here, we assembled the complete mitochondrial genome of D. loddigesii and discovered that its genome possessed a complex multi-chromosome structure. The mitogenome of D. loddigesii consisted of 17 circular subgenomes, ranging in size from 16,323 bp to 56,781 bp. The total length of the mitogenome was 513,356 bp, with a GC content of 43.41%. The mitogenome contained 70 genes, comprising 36 protein-coding genes (PCGs), 31 tRNA genes, and 3 rRNA genes. Furthermore, we detected 403 repeat sequences as well as identified 482 RNA-editing sites and 8154 codons across all PCGs. Following the sequence similarity analysis, 27 fragments exhibiting homology to both the mitogenome and chloroplast genome were discovered, accounting for 9.86% mitogenome of D. loddigesii. Synteny analysis revealed numerous sequence rearrangements in D. loddigesii and the mitogenomes of related species. Phylogenetic analysis strongly supported that D. loddigesii and D. Amplum formed a single clade with 100% bootstrap support. The outcomes will significantly augment the orchid mitochondrial genome database, offering profound insights into Dendrobium’s intricate mitochondrial genome architecture.