Transcriptome De Novo Assembly Sequencing And Gene Expression Analysis Of Alexandrium Catenella(Dinoflagellate)

As an ecological phenomenon, harmful algal blooms (HABs) or ‘red tides’ hasobtained wide attention, for its serious impact on the human health, environment,aquaculture, fisheries and tourism. The outbreak of ‘red tides’ have been studied in thefield of ecology and physiology. However, the research is limited in the field ofmolecular mechanism. Alexandrium Lebour Balech is an important dinoflagellate ofHABs. The dinoflagellate Alexandrium catenella forms ‘red tides’ producing paralyticshellfish poisoning (PSP). In this study, A. catenella transcriptomes from three stageswere sequenced using Illumina paired-end sequencing technology, respectively.Assembled transcripts of the three samples were clustered to unigenes. A total of118,304unigenes were identified with65.9%（77,936）unigenes were annotated withknown proteins based on sequence similarities, among which24,149and22,956unigenes were assigned to gene ontology categories (GO) and clusters of orthologousgroups (COG), respectively. Furthermore, with Kyoto Encyclopedia of Genes andGenomes Pathway database (KEGG),16,467unigenes were mapped onto322pathways. The genetic facts derived from the transcriptome dataset were suggestedand discussed. Further analysis was carried out for unigenes related to linker histone,the result exhibited that H1genes of A. catenella may have ancient origins and theymay be originated from the ancient primary endosymbiosis without the divergence ofextant green and red algae. In addition, we identified190unigenes involved inendocytosis pathway, including two important factors in clathrin-dependentendocytosis, we speculated clathrin-dependent endocytosis may play a certain rolewith respect to the heterotrophy of A. catenella. As for the structure of these unigenes,1,143simple sequence repeats (SSRs) were identified, in which the tri-nucleotiderepeat motif (69.3%) was the most abundant; a conserved22-nt spliced leader (SL)was identified in21unigenes.Based on the expression analysis of unigenes from three samples, we got the different expression unigenes, among which a unigene annotated to glycine-richprotein (GRP) was identified. We got the full-length cDNA of grp through rapidamplification of cDNA ends, structure analysis indicated that there was a conserveddomain of cold-shock protein, and phylogenetic analysis revealed that deduced aminoacid sequence of grp tend to cluster together with cold shock domain protein.Moreover, we verified the expression of grp by real-time PCR. The result of real-timePCR indicated that the expression of grp in induced logarithmic phase was higherthan in logarithmic phase, which was higher than in lag phase. The expression patternof grp was coincident with the ability of cell division. We speculate that grp wasclosely related to cell division, which may trigger a new breakthrough for the study ofred tide.