# Comparative Genomics of Bryopsis hypnoides: Structural Conservation and Gene Transfer Between Chloroplast and Mitochondrial Genomes

## TL;DR

This study analyzes the chloroplast and mitochondrial genomes of Bryopsis hypnoides, revealing structural features and evidence of gene transfer between them.

## Contribution

The study provides the first complete and annotated chloroplast and mitochondrial genomes of B. hypnoides and identifies potential gene transfer between them.

## Key findings

- The chloroplast genome favors A/T repeats, while the mitochondrial genome prefers C/G repeats.
- Both organellar genomes prefer codons ending in A/T, with a stronger bias in the chloroplast genome.
- Sixteen fragments with high sequence identity were found between the two genomes, suggesting potential gene transfer.

## Abstract

Bryopsis hypnoides, a unicellular multinucleate green alga in the genus Bryopsis, plays vital ecological roles and represents a key evolutionary link between unicellular and multicellular algae. However, its weak genetic baseline data have constrained the progress of evolutionary research. In this study, we successfully assembled and annotated the complete circular chloroplast and mitochondrial genomes of B. hypnoides. The chloroplast genome has a total length of 139,745 bp and contains 59 protein-coding genes, 2 rRNA genes, and 11 tRNA genes, with 31 genes associated with photosynthesis. The mitochondrial genome has a total length of 408,555 bp and contains 41 protein-coding genes, 3 rRNA genes, and 18 tRNA genes, with 18 genes involved in oxidative phosphorylation. Based on the data, we conducted a genetic comparison involving repeat sequences, phylogenetic relationships, codon usage preferences, and gene transfer between the two organellar genomes. The major results highlighted that (1) the chloroplast genome favors A/T repeats, whereas the mitochondrial genome prefers C/G repeats; (2) codon usage preference analysis indicated that both organellar genomes prefer codons ending in A/T, with a stronger bias observed in the chloroplast genome; and (3) sixteen fragments with high sequence identity were identified between the two organellar genomes, indicating potential gene transfer. These findings provide critical insights into the organellar genome characteristics and evolution of B. hypnoides.