| The deep-sea hydrothermal vent regions show extremes in dark,low oxygen,high pressure,unstable temperature,and high content of toxic substances such as hydrogen sulfide and heavy metals.Nevertheless,the deep-sea hydrothermal vent is an important habitat for deep-sea organisms,and some organisms have been highly adapted to this extreme environment,during evolution,forming a chemosynthetic-based ecosystem around hydrothermal vents.Most of the species in hydrothermal vents are endemic.Gigantopelta aegis（Gastropoda: Peltospiridae）from Longqi vent field in the Southwest Indian Ridge,is one of the endemic species in deep-sea hydrothermal vents.In this study,the transcriptome of five snails were sequenced and analyzed.Meanwhile,two antimicrobial peptide genes identified from G.aegis were expressed and their functional characteristics were detected.A total of 268,673,302 raw reads were obtained from the transcriptome of five snails（Ga1,Ga2,Ga3,Ga4,Ga5）.The averages of Q20 and Q30 were 97.18% and92.44%,respectively,and the GC contents were ranged from 41.99% to 43.35%,indicating the quality of the sequencing data.A total of 277,717 unigenes were assembled,with N50 lengths of 1,861 bp and N90 lengths of 456 bp.41.26% of unigenes（114,601）were annotated in at least one database.Both KEGG and KOG annotations indicated that a large number of unigenes from G.aegis were related to“signal transduction mechanisms”.Based on cluster analysis of differential gene expression levels and Pearson pairwise correlations between samples,significant genetic differences between Ga2 and other individuals were found.The transcriptome data of five individuals were reanalyzed,respectively.The COI sequences of the five snail individuals were extracted from the transcriptome data to construct a species tree with other gastropod relative species.Two different COI genes were identified in the transcriptome of Ga2,which clustered with COI sequences of G.aegis and Dracogyra subfuscus,respectively.We using 860 sets of single-copy homologous gene orthologs from the genome of six closely related gastropod species and the transcriptome of the five snail individuals to build a ultrametric tree,confirming that Ga1,Ga3,Ga4,Ga5 and G.aegis are the same species,but there are genetic differentiation among them.Ga2 was found to be clustered with D.subfuscus.However,the genetic distance between Ga2 and G.aegis was closest.Two antimicrobial peptide genes gigantin-1 and gigantin-2 with antibacterial activity were screened out from the transcriptome data of Gigantopelta.Gene gigantin-1 was expressed with the expression system of Chlamydomonas reinhardtii,and the antibacterial activity was studied.It was found that the antimicrobial peptide gigantin-1 can inhibit the growth of gram-positive bacteria,but the inhibitory effect on gramnegative bacteria was ambiguous.Meanwhile,gigantin-1 shows the characteristics of stability at high temperature,high salinity resistance and extreme p H resistance;The antibacterial peptide gigantin-2 synthesized by chemical method can inhibit both grampositive and gram-negative bacteria.Gigantin-2 also has the characteristics of good thermal stability,high salinity resistance and extreme p H resistance.The gigantin-2 also show low hemolytic activity on fish blood cells,indicating its high safety.Therefore,the antibacterial peptide genes of Gigantopelta will find their way into biomedical and biotechnological applications.This study insight our understanding on the diversity of animals in the Longqi vent field in the Southwest Indian Ocean,and also discovered the genetic differentiation of Gigantopelta individuals.In addition,we provided molecular data for the extreme environmental adaptation mechanism of Gigantopelta,and obtained two antibacterial peptide functional genes with potential of application. |
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