Mitochondrial genomes and phylogenomic analysis of Ulva lactuca Linnaeus (Ulvophyceae, Chlorophyta)

Two mitogenomes of Ulva lactuca Linnaeus, one from Florida, USA and another nearly complete mtDNA from Chile, had previously been sequenced. Here, the complete mitogenome of U. lactuca from Shantou, China was sequenced and compared with them. The circular-mapping mitogenome of U. lactuca was 62,021 bp in size and 407 bases longer than that from the USA. The average sequence identity in gene sequence regions was 99.8% among these three U. lactuca mtDNAs. Differences in genome sizewere mainly caused by duplication mutations and insertion/deletion mutations of short DNA sequences. Two intergenic regions (nad6-trnS and trnF-trnG) contained long tandem repeats which displayed a high level of variation in repeat sequences and copy numbers, indicating fast mutation rates in these regions. The phylogenomic analysis revealed that these three samples of U. lactuca formed a strongly supported clade. The mitogenome can be used to understand the phylogeography and population genetics in Ulva on a global scale.