Comparative analysis of four essential Gracilariaceae species in China based on whole transcriptomic sequencing

Three Gracilaria species,G.chouae,G.blodgettii,G.vermiculophylla and a close relative species,Gracilariopsis lemaneiformis which is now nominated as Gracilaria lemaneiformis,are the typically indigenous species which are important resources for the production of special proteins,phycobilisomes,special carbohydrates,and agar in China.In this study,de novo transcriptome sequencing on these four species using the next generation sequencing technology was performed for the first time.Functional annotations on assembled sequencing reads showed that the transcriptomic profiles were quite different between G.lemaneiformis and other three Gracilaria species.Comparative analysis of differential gene expression related to carbohydrate and phycobiliprotein metabolisms also showed that the expression profiles of these essential genes were different in four species.The genes encoding allophycocyanin,phycocyanin and phycoerythrin were further examined in four species and their deduced amino acid sequences were used for phylogenetic analysis to confirm that G.lemaneiformis had close relationship to genus Gracilaria,as well as that within genus Gracilaria,G.chouae had closer relationship to G.vermiculophylla rather than to G.blodgettii.The de novo transcriptome study on four species provided a valuable genomic resource for further understanding and analysis on biological and evolutionary study among marine algae.