The large mitochondrial genome of Syndiclis anlungensis (Lauraceae): Genome structure, comparative analysis, and phylogenetic relationships among Syndiclis species.
The complete mitochondrial genome (mitogenome) of Syndiclis anlungensis, a critically endangered tropical tree, was determined in this study. The mitogenome spans 2,368,454 bp across four contigs and harbors 41 protein-coding genes, 22 tRNA genes, and three rRNA genes. Potential mutation regions, including 1317 repeat sequences and 698 simple sequence repeats (SSRs), were accurately located in the S. anlungensis mitogenome. Sixty-five transferred fragments of the repeats were found between its mitochondrial and chloroplast genomes. When compared to three other Laurales mitogenomes, extensive gene order shuffling is evident, leaving only five conserved gene clusters intact. Codon usage analysis reveals a pronounced A/T bias in both mitochondrial and chloroplast genes, and three mitochondrial genes (atp9, rps19, and sdh3) stand out for their high divergence across eleven Syndiclis taxa. Selection analyses indicate strong purifying pressure on rpl2, rpl16, and sdh3 (Ka/Ks < 1), with no positive selection detected. Using 41 mitochondrial protein-coding gene sequences from sixteen and three individuals of Syndiclis and Beilschmiedia species, respectively, our phylogenetic tree recovers Syndiclis as monophyletic, with two well-supported clades: one includes S. anlungensis, S. chinensis, S. lotungensis, S. marlipoensis, and a putative new Syndiclis species from Yunnan; the other contains S. furfuracea, S. hongkongensis, S. kwangsiensis, and three putative new Syndiclis species from Guangdong and Vietnam.