High-throughput Genome Sequencing of an Aquaculture Crop, Susabi-nori (Pyropia yezoensis)

A laver, nori, is one of the most important seafood in East Asia. This seaweed is in particular utilized as a material of sushi rolls in Japan. Nori is so-called a red alga and classified into the order Bangiales (Rhodophyta), but the genomic information on this lineage has been very poor compared to other algae. In addition, genome sequencing of nori has been much difficult until now, because symbiotic bacteria are tightly attaching to the surface of thalli of nori, resulting in heavy DNA contamination. To remove such bacteria, in the current study, we developed axenic protoplasts of susabi-nori (Pyropia yezoensis) with enzymatic treatment. Thus we successfully sequenced the nuclear genome of P. yezoensis using high-throughput sequencing technologies. The assembled contig size of the P. yezoensis nuclear genome was approximately 43 megabases in total, which is much smaller than a previously estimated genome size (~260 megabases). A total of 10,327 gene models were predicted by gene-finding software, and most of the genes lack introns or have shorter introns compared to other large-genome algae. Moreover, we compared the gene repertoire among the already-sequenced algal and plant genomes, and found novel genes that have never reported in red algae. In particular, we found gene candidates related to the color trait of red algae from the P. yezoensis nuclear genome. These findings will provide significant insights into the fields of not only aquaculture and food industry but also algal biology.