In this paper, we review cultural history, mariculture and taxonomic work to date for Porphyra sensu lato (bladed Bangiales) in China. The bladed Bangiales are a red seaweed group with high species biodiversity and economic value. In China, species occur along the length of the coast and are highly integrated into the country’s culture. Chinese people have used the bladed Bangiales as food and pharmaceuticals for about 1700 years with many references to these seaweeds in ancient books. The mariculture of bladed Bangiales in China also has a long history and an industry has been established based on some species, notably Pyropia yezoensis. The scientific study of the taxonomy of the bladed Bangiales in China began in the late 1920s and to date, based on morphological identification, 25 species and five varieties have been recorded for China, of which 12 species are considered to be endemic to the country. The majority of species have distribution data showing evidence of possible changes due to increasing water temperatures along the coast. The global biodiversity of the bladed Bangiales has been revealed using molecular approaches. This points to the need for molecular taxonomy of Chinese material to document species diversity and distribution, particularly as it includes the wild stocks for seaweed cultivation and because coastal habitats are increasingly impacted by the increasing human population and an expanding mariculture industry. There is a considerable body of literature on the bladed Bangiales in China, but much of it is Chinese and in obscure publications, so we review it here for the benefit of readers worldwide.

Carotene hydroxylases catalyze the hydroxylation of α- and β-carotene hydrocarbons into xanthophylls. In red algae, β-carotene is a ubiquitously distributed carotenoid, and hydroxylated carotenoids such as zeaxanthin and lutein are also found. However, no enzyme with carotene hydroxylase activity had been previously identified in red algae. Here, we report the isolation of a gene encoding a cytochrome P450-type carotene hydroxylase (PuCHY1) from Porphyra umbilicalis, a red alga with an ancient origin. Sequence comparisons found PuCHY1 belongs to the CYP97B subfamily, which has members from different photosynthetic organisms ranging from red algae to land plants. Functional complementation in Escherichia coli suggested that PuCHY1 catalyzed the conversion from β-carotene to zeaxanthin. When we overexpressed PuCHY1 in the Arabidopsis thaliana chy2 mutant, pigment analysis showed a significant accumulation of hydroxylated carotenoids, including neoxanthin, violaxanthin, and lutein in the leaves of transgenic plants. These results confirmed a β-hydroxylation activity of PuCHY1, and also suggested a possible ϵ-hydroxylation function. The pigment profile and gene expression analyses of the algal thallus under high-light stress suggested that P. umbilicalis is unlikely to operate a partial xanthophyll cycle for photoprotection.

The cultivation of red seaweeds for food (nori), agar and carrageenans is the basis of a valuable industry. However, taxonomic knowledge of these cultivated seaweeds and their wild relatives has not kept pace with advances in molecular systematics despite the fundamental importance of being able to identify commercially important species and strains, discover cryptic and endemic taxa and recognize non-native species with potentially damaging diseases and epiphytes. This review focuses on molecular taxonomic advances in the cultivated red algae with the highest commercial value globally: Eucheuma and Kappaphycus, Porphyra sensu lato and Gracilaria. All three groups are similarly taxonomically challenging: speciose, morphologically plastic, with poorly resolved species boundaries. Eucheuma and Kappaphycus are frequently misidentified and the molecular markers cox2-3 spacer, cox1 and RuBisCO spacer have helped in understanding phylogenetic relationships and identifying new species and haplotypes. In Porphyra sensu lato (Bangiales) species identification and phylogenetic relationships were highly problematic until a taxonomic revision based on a two-gene phylogeny (18S and rbcL) resulted in nine genera of bladed species. Pyropia, with at least 89 species, three in nori cultivation, has potential for new commercial evaluation. In Gracilaria sensu lato, earlier efforts to resolve species-level taxonomy and generic descriptions were superseded by application of molecular tools, including DNA sequences of the RuBisCO spacer, rbcL gene, 18S and the ITS region. Studies of these cultivated red algal genera highlight the need for a robust taxonomy, a more standardized approach to the molecular markers used and a comprehensive dataset for each representative species. Current work on DNA-based species delimitation, the emergence of high throughput sequencing, multi-gene phylogenies, publication of whole genomes (e.g. Porphyra umbilicalis) and genomes in the pipeline (e.g. Gracilaria) are increasingly improving our understanding of phylogenomic relationships and species relationships. This knowledge, in turn, can then be applied to improving red seaweed aquaculture.