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Nori is the cultivated seaweed with the highest market value in the world. Monospores from the thalli reseed the cultivating nets and provide useful secondary seedlings in nori farming, but the underlying molecular basis remains unclear. To explore crucial genes and pathways related to monospore-producing process in Phycocalida chauhanii (Pyropia chauhanii), transcriptomic analysis over the time-course of key developmental stages was carried out. According to comparative analysis, a total of 19,490 differentially expressed genes (DEGs) were identified. Based on time series trend clustering analysis, 7294 DEGs were enriched in a predominant profile 45, in good accordance with the actual temporal monospore-producing processes, exhibiting an expression trend of first upregulated and then downregulated. Gene Ontology (GO) analysis revealed that the function of these DEGs were top three enriched in GO biological processes of positive regulation of GTPase activity, signal transduction, and protein phosphorylation. KEGG pathway analysis indicated that these DEGs were top three enriched in the “mitogen-activated protein kinase (MAPK) signaling pathway, regulation of autophagy, and endocytosis”. Besides, the expression levels of 12 selected DEGs were validated by real-time quantitative PCR and proved the accuracy of RNA-seq results. Collectively, these findings provide a comprehensive landscape of the molecular mechanism underlying the formation and release of monospores, which might serve as essential basis for the identification of key genes that contribute to monospore formation.

Calmodulin (CaM) plays an important regulatory role in plant growth and development. In this study, on the basis of previous transcriptomic annotation a homolog of CaM gene (Pc-CaM7) was identified from the red alga Phycocalida chauhanii (previously known as Porphyra chauhanii). It encoded a 151 amino acids protein with 4 EF-hand regions, which was the typical structure of calmodulin family proteins. Evolutionary analysis showed that Pc-CaM7 shared conserved orthologous relationships with CaMs from Neoporphyra haitanensis (formerly Pyropia haitanensis), Porphyra umbilicalis, and Gracilariopsis chorda. During the developmental period of P. chauhanii gametophytic germlings from 25- to 50-day-old, the asexual archeospores were continuedly released from the marginal region of blades, followed by the emergence of spermatangia from 40-day-old germlings. Based on quantitative real-time PCR analysis, it showed that expression trend of Pc-CaM7 was correlated with the rule of archeospores’ formation and release, whereas in N. haitanensis without archeospore characteristic, the expression pattern of the orthologous gene (Pha_00404) was different, which increased and reached a plateau during the same developmental period. These findings suggested that Pc-CaM7 may be involved in the process of archeospores formation and release, which may provide a foundation for understanding the molecular mechanisms of asexual reproduction in Bangiales.

As an economically important marine seaweed, Pyropia yezoensis can be asexually reproduced via archeospores. However, the molecular mechanism of archeospore formation remains unclear. In this study, we characterized the transcriptomes of two strains of Py. yezoensis, which are strain W′ with abundant archeospores and strain W with scarce archeospores. The 25- and 35-day-old gametophytic blades of both strains were sampled for RNA sequencing. Based on comparative transcriptomic analysis, a large number of differential expressed genes (DEGs) of four pairwise groups between samples were generated. In an effort to identify the genes related to archeospore formation, 415 consensus DEGs reflecting the difference between two strains were investigated. Gene ontology and KEGG analysis revealed that the function for these DEGs was enriched in various processes, such as translation, ribosome assembly, RNA methylation, vesicles assembly, intracellular localization of organelles, and endocytosis. According to functional analysis on 80 selected DEGs, it indicated that genes involved in calcium and MAPK signaling pathway, cytoskeletal movement, and cell wall degradation were related to the formation of archeospores. The accuracy of RNA-seq results was validated by quantitative real-time PCR of 8 selected DEGs. These findings suggest that the molecular mechanism of archeospore formation in Py. yezoensis is sophisticated and our results will serve as an essential foundation for further studies.