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Peroxisome proliferator activated receptors (PPAR) are kinds of key transcriptional factors in regulating LC-PUFA biosynthesis. Until now, little is known about PPAR in marine molluscs as well as in other invertebrates. Sinonovacula constricta is the first marine mollusc that is proved to possess the complete LC-PUFA biosynthetic pathway, and it can be a perfect representative to clarify this situation. In this study, the molecular properties of S. constricta PPAR were characterized, and corresponding potential regulatory roles in S. constricta Δ6 fatty acyl desaturase (Fad) transcription were estimated by dual luciferase assay. Results showed that two PPAR homologs (PPAR_a and _b) were identified in S. constricta. They both contain typical features of vertebrate PPAR, suggesting highly conserved functional regions in PPAR. By phylogenetic comparison, they are clearly different with vertebrate PPAR and can be divided into two distinctive sub-groups. Moreover, they show a high expression level in gill, labial palps, mantle and intestine. Their down-regulated expressions in trochophore larva and veliger larva might be attributed to food-deprivation. Additionally, the transcriptional activity of S. constricta Δ6 Fad promoter was significantly activated by both PPAR_a and _b, indicating that S. constricta PPAR might play a role in the regulation of LC-PUFA biosynthesis. To our knowledge, this is the first systematic analysis of PPAR in a marine mollusc. The results will provide a valuable reference for further researches on the function of marine molluscan PPAR and their underlying mechanisms in regulating LC-PUFA biosynthesis. [ABSTRACT FROM AUTHOR]

Background: Sinonovacula constricta is an economically important bivalve species in China, Korea and Japan that widely resides in estuarine and coastal areas where salinity fluctuates rapidly. However, little is known about its adaptation mechanisms to acute salt stresses. Objective: To reveal the underlying molecular mechanisms involved in acute salt stresses in juvenile S. constricta. Methods: Nine cDNA libraries (triplicate each trial) were established from juvenile S. constricta, which were subjected to low salinity (5 psu), optimal salinity (15 psu) and high salinity (25 psu) for 6 h, respectively. Results: Illumina sequencing generated 478,587,310 clean reads totally, which were assembled into 427,057 transcripts of 246,672 unigenes. Compared with the control, 1259 and 2163 differentially expressed genes (DEGs) were identified under acute low and high salt stresses, respectively. GO and KEGG enrichment analyses of DEGs revealed that several key metabolic modulations were mainly responsible for the acute salt stresses. According to the significantly highlighted KEGG pathways, some key DEGs were identified and discussed in details. Notably, based on which, some potential osmolytes were further speculated. Conclusion: Here, we carried out a unique report of comparative transcriptome analyses in juvenile S. constricta in response to acute salt stresses. The identified DEGs and their significantly enriched GO terms and KEGG pathways were critical for understanding and further investigating the underlying the physical and biochemical performances, and ultimately facilitated S. constricta breeding. Besides, the transcriptome data greatly enriched the genetic information of S. constricta, which were valuable for promoting its molecular biology researches. [ABSTRACT FROM AUTHOR]

Volatiles with a pleasant smell are typical characteristics of both raw and cooked seafood. However, the effect of salinity on volatiles in marine bivalves remains unclear. In the current study, the volatiles in raw and cooked Sinonovacula constricta cultured under different salinities were investigated by head space-solid phase microextraction and gas chromatography-mass spectrometry. Overall 28 volatiles were identified in the raw samples and mainly comprised 1-pentanol (15.32-23.95%), 1,5-octadien-3-ol (14.20-16.73%) and 1-octen-3-ol (14.20-15.63%). A total of 41 volatiles, dominated by pentanal (32.33-46.80%), 1-pentanol (10.88-16.48%) and hexanal (5.64-13.70%), were determined in the cooked samples. Irrespective of whether they were raw or had been cooked, S. constricta cultured under high salinity possessed more abundant volatiles than those reared under low salinity. When the culture salinity of S. constricta was raised, changes in the volatile content occurred. For S. constricta cultured at low salinity, rearing at high salinity for several days prior to harvest could greatly improve the volatile content. This finding is of value for the improvement of volatiles important for odor and taste in other marine bivalves. [ABSTRACT FROM AUTHOR]