Expressed sequence tags from cDNA library prepared from gills of the swimming crab, Portunus trituberculatus

The swimming crab, Portunus trituberculatus, is an important marine fishery and aquaculture species. Although P. trituberculatus is a euryhaline species, water salinity condition influenced its distribution and migration route. In order to understand molecular mechanism of osmoregulation and discover genes involved in salinity adaptation, expressed sequence tags (ESTs) from gills of this crab were characterized under salinity challenges. From 4433 high-quality sequences, 2426 unique genes including 238 contigs and 2188 singlets were obtained. Only one third of the unigenes are homologous with known proteins, others are found only in the swimming crab, suggesting a high percent of unknown genes in this species. Nearly 292 transcripts, which accounted for about 12% (292/2426) of total unique genes and about 14% (629/4433) of the total sequenced ESTs, were candidate genes responsive to salinity challenge based on current knowledge. Gene ontology annotation further grouped these genes into seven function categories including: reactive oxygen scavengers (5.4%), transporter protein (15.8%), stress protein (11.0%), signal transduction (13.7%), protein synthesis and destination (22.4%), transcription (13.7%), and metabolism/energy (17.5%) indicating salinity adaptation may be involved with a series of cellular processes. This study represents the first functional profiling of genes expressed in P. trituberculatus gill and provides so far the largest gene collection of this species. The pertinent sequence would greatly facilitate the elucidating molecular mechanisms underlying salinity adaptation in this species.