Advances in Research on Diatom Chitin Metabolism

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Advances in Research on Diatom Chitin Metabolism

Posted By Johnson Brown     May 17, 2023    

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Recently, the Seaweed Genetics and Development Team of the Institute of Oceanography, Chinese Academy of Sciences published a research paper entitled "Characterization of a marine diatom chitin synthase using a combination of meta-omics, genomics and heterologous expression approaches" in the journal mSystems. This paper comprehensively used methods such as meta-omics, genomics and heterologous function verification to analyze the chitin synthase of marine diatoms. It provides a new understanding, and also lays a foundation for the biological significance and regulation mechanism of diatom β-chitin synthesis.

 

Diatoms are the main contributors to the primary productivity of the ocean. About 40% of the CO2 absorbed by the ocean is fixed by diatoms, which is equivalent to the amount of carbon sequestered by tropical rainforests. Chitin is an important carbon accumulation product of diatoms and the most important source of carbon and nitrogen in the marine environment. The ocean can synthesize billions of tons of chitin every year, and its synthesis and degradation play a key role in the carbon and nitrogen cycle of marine ecosystems. Although it was reported in 1965 that diatoms can synthesize chitin, the research for more than half a century has focused on cytological observation and chemical structure analysis, and there is no report on the analysis of the synthesis and degradation mechanism of diatom chitin from molecular biology.

 

In the early stage, the Seaweed Genetics and Development Research Group of the Institute of Oceanography cooperated with the algae genomics team of the Ecole Normale Supérieure in France to carry out original work on the analysis of the metabolic mechanism of diatom chitin. Combined with multi-omics data mining and functional verification of specific genes (TpCDA, TwCDA), it was found that the central class diatom chitin-related metabolic enzymes have complex cellular localizations such as chloroplasts, mitochondria, and endoplasmic reticulum, and the abundance of CDAs genes is higher. Chain polymer chitin has stronger catalytic ability, and has both chitin deacetylase and chitinase activities. The related results explain the potential reasons for the high synthesis ability of central class diatom chitin and its derivatives (New Phytologist, 2019; Marine Drugs, 2021), also provides new ideas for the green industrial preparation of chitosan and chitooligosaccharides (BMC Plant Biology, 2021; Metabolites, 2023).

 

Considering the important ecological significance of chitin for the global carbon and nitrogen cycle, the team focused on the global sampling big data of Tara Oceans, and mined 4939 gene sequences related to chitin metabolism from the diatom metatranscriptome, among which chitinase is mainly found in diatom species with large particle size, while chitin-binding protein (CBM_14) is only distributed in the Southern Ocean, indicating that it plays a special role in the polar environment. At the same time, by searching the Marine Eukaryotic Microbial Transcriptome Database (MMETSP), PhycoCosm and PLAZA diatomomics data sets, it was found that in addition to Thalastrones, Mediophyceae and Thalassionemales may be potential natural synthesizers of β-chitin. The research on the mechanism of biosynthetic pathway cannot avoid the functional verification of key genes. The team used two highly efficient heterologous genetic transformation systems (Saccharomyces cerevisiae and Phaeodactylum tricornutum) to verify that chitin synthase (TpCHS) in Thalassiosira pseudonana has the biological function of catalyzing the synthesis of chitin sugar chains. It is worth mentioning that in the transgenic research, the team found an interesting phenomenon that although Phaeodactylum tricornutum can highly express TpCHS1, the cell morphology is abnormal and the growth rate decreases. Combined with laser confocal microscopy observation and cell cycle marker gene expression analysis, it was found that TpCHS1 is located in the Golgi apparatus and cell membrane system, and is closely related to cell division, while the decrease in growth rate of overexpressed lines may be related to the G2/M in cell cycle regulation. It is related to the suppression of checkpoints during the period.

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