Abstract
BackgroundMytilisepta virgata is a marine mussel commonly found along the coasts of Japan. Although this species has been the subject of occasional studies concerning its ecological role, growth and reproduction, it has been so far almost completely neglected from a genetic and molecular point of view. In the present study we present a high quality de novo assembled transcriptome of the Japanese purplish mussel, which represents the first publicly available collection of expressed sequences for this species.ResultsThe assembled transcriptome comprises almost 50,000 contigs, with a N50 statistics of ~1 kilobase and a high estimated completeness based on the rate of BUSCOs identified, standing as one of the most exhaustive sequence resources available for mytiloid bivalves to date. Overall this data, accompanied by gene expression profiles from gills, digestive gland, mantle rim, foot and posterior adductor muscle, presents an accurate snapshot of the great functional specialization of these five tissues in adult mussels.ConclusionsWe highlight that one of the most striking features of the M. virgata transcriptome is the high abundance and diversification of lectin-like transcripts, which pertain to different gene families and appear to be expressed in particular in the digestive gland and in the gills. Therefore, these two tissues might be selected as preferential targets for the isolation of molecules with interesting carbohydrate-binding properties.In addition, by molecular phylogenomics, we provide solid evidence in support of the classification of M. virgata within the Brachidontinae subfamily. This result is in agreement with the previously proposed hypothesis that the morphological features traditionally used to group Mytilisepta spp. and Septifer spp. within the same clade are inappropriate due to homoplasy.
Highlights
Mytilisepta virgata is a marine mussel commonly found along the coasts of Japan
The high quality transcriptome of Mytilisepta virgata Following the application of quality filters, the de novo transcriptome assembly of M. virgata comprised 49,501 contigs with an average length of 679 nucleotides (Table 2)
This number, apparently rather high if compared to the number of annotated genes in bivalve genomes (e.g. ~26,000 in C. gigas and ~33,000 in P. fucata) [40, 47], is possibly justified by at least three factors: (i) the poor knowledge of bivalve non-coding RNAs, that are abundant in mussels [14], including in M. virgata, where they account for 71% of the assembled contigs; (ii) the partial fragmentation of mRNAs in smaller contigs; (iii) the high genomic complexity and heterozygosity of the genome of mytiloids, previously pointed out in Mytilus spp. [16]
Summary
Mytilisepta virgata is a marine mussel commonly found along the coasts of Japan. this species has been the subject of occasional studies concerning its ecological role, growth and reproduction, it has been so far almost completely neglected from a genetic and molecular point of view. More than a decade ago, molecular studies based on Cytochrome c oxidase subunit I (COI) first pointed out that M. virgata and the morphologically similar Septifer excisus (Wiegmann, 1837) pertained to two different clades within the order Mytiloida [8] This observation is strongly supported by a recent study by Trovant and colleagues, which reported that COI and 18S/28S– based phylogeny identified both M. virgata and Mytilisepta bifurcata (Conrad, 1837) as members of the same clade, together with Perumytilus purpuratus (Lamarck, 1819) and Brachidontes rostratus (Dunker, 1857) (both pertaining to the Brachidontinae family), but distantly related to Septifer bilocularis [9]. The authors further suggested that Mytilisepta should be retained as a separate genus within Brachidontinae and that the septum structure involved in the insertion of the adductor muscle and used for the current morphological classification of different species within the Septifer genus is the product of homoplasy
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