Phylogeny of Saccharina and Laminaria (Laminariaceae, Laminariales, Phaeophyta) in sequence-tagged-site markers

Laminaria and Saccharina have recently been recognized as two independent clades from the former genus Laminaria. Traditional morphological taxonomy is being challenged by molecular evidence from both nucleus and plastid. Intensive work is in great demand from the perspective of genome colinearity. In this study, 118 sequence-tagged site (STS) markers were screened for phylogenetic analyses, 29 based on genome sequences, while 89 were based on expressed sequence tag (EST) sequences. EST-based STS marker development (29.37%) had an effi ciency twice as high as genome-sequence-based development (9.48%) as a result of high conservation of gene transcripts among the relative species. S. ochotensis, S. religiosa, S. japonica, and L. hyperborea showed great homogeneity in all 118 STS markers. Our result supports the view that the diversifi cation between the genera Saccharina and Laminaria was a more recent event and that Saccharina and Laminaria shared high phylogenetic affi nity. However, when it came to the single nucleotide polymorphism (SNP) level among the 41 SNPs, L. hyperborea owned 29 unique SNPs against 12 within the left three Saccharina species and 12 of the 13 indels were supposedly unique for L. hyperborea, indicated by its high variability. Originating from homologous ancestors, species between the recently diverged genera Laminaria and Saccharina may have taken in enough mutations at the SNP level only, in spite of different evolutionary strategies for better adaptation to the environment. Our study lays a solid foundation from a new perspective, although more accurate phylogenetic analysis is still needed to clarify the evolutionary traces between the genera Saccharina and Laminaria.