De novo sequencing and comparative analysis of three red algal species of Family Solieriaceae to discover putative genes associated with carrageenan biosysthesis

Betaphycus gelatinus, Kappaphycus alvarezii and Eucheuma denticulatum of Family Solieriaceae, Order Gigartinales, Class Rhodophyceae are three important carrageenan-producing red algal species, which produce different types of carrageenans, beta (beta)-carrageenan, kappa (kappa)-carrageenan and iota (iota)-carrageenan. So far the carrageenan biosynthesis pathway is not fully understood and few information is about the Solieriaceae genome and transcriptome sequence. Here, we performed the de novo transcriptome sequencing, assembly, functional annotation and comparative analysis of these three commercial-valuable species using an Illumina short-sequencing platform Hiseq 2000 and bioinformatic software. Furthermore, we compared the different expression of some unigenes involved in some pathways relevant to carrageenan biosynthesis. We finally found 861 different expressed KEGG orthologs which contained a glycolysis/gluconeogenesis pathway (21 orthologs), carbon fixation in photosynthetic organisms (16 orthologs), galactose metabolism (5 orthologs), and fructose and mannose metabolism (9 orthologs) which are parts of the carbohydrate metabolism. We also found 8 different expressed KEGG orthologs for sulfur metabolism which might be importantly related to biosynthesis of different types of carrageenans. The results presented in this study provided valuable resources for functional genomics annotation and investigation of mechanisms underlying the biosynthesis of carrageenan in Family Solieriaceae.