De novo transcriptome of the pallial gland of the date mussel (Lithophaga lithophaga).

Lithophaga lithophaga is a rock-boring bivalve with an ability to dissolve carbonate substrata with its siphonal and pallial gland secretions. However, the molecular mechanism that enables this species to bore into calcareous rocks is not yet known. In order to identify genes potentially involved in chemical boring we performed transcriptome sequencing of pallial-gland tissue samples of L. lithophaga. Transcriptome sequencing using an Ion Torrent platform generated 60.563 million clean reads with an average read length of 96 bp. De novo assembly of clean reads produced 62,490 contigs with a mean length of 408 bp. Since the boring mechanism is attributed to calcium-binding proteins, the search focused on transcripts capable of binding this element. In all, 178 genes with calcium-binding ability were found to be expressed in the pallial gland of L. lithophaga. Annexins, calreticulin, phospholipase A2 and V-type proton-ATPases were considered as possible candidate chemical-boring genes due to their known function and involvement in various other biological processes: e.g. ion transport, cellular catabolic process, protein folding. Transcriptome analysis of L. lithophaga revealed a set of candidate genes putatively associated with chemical boring. The selected set of genes will be studied further to verify their expression patterns and their possible involvement in the rate of chemical boring in L. lithophaga.