Comparative Gene Analysis Focused on Silica Cell Wall Formation: Identification of Diatom-Specific SET Domain Protein Me
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ORIGINAL ARTICLE
Comparative Gene Analysis Focused on Silica Cell Wall Formation: Identification of Diatom-Specific SET Domain Protein Methyltransferases Michiko Nemoto 1 & Sayako Iwaki 1 & Hisao Moriya 1 & Yuki Monden 1 & Takashi Tamura 1 & Kenji Inagaki 1 & Shigeki Mayama 2 & Kiori Obuse 1 Received: 29 October 2019 / Accepted: 7 May 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Silica cell walls of diatoms have attracted attention as a source of nanostructured functional materials and have immense potential for a variety of applications. Previous studies of silica cell wall formation have identified numerous involved proteins, but most of these proteins are species-specific and are not conserved among diatoms. However, because the basic process of diatom cell wall formation is common to all diatom species, ubiquitous proteins and molecules will reveal the mechanisms of cell wall formation. In this study, we assembled de novo transcriptomes of three diatom species, Nitzschia palea, Achnanthes kuwaitensis, and Pseudoleyanella lunata, and compared protein-coding genes of five genome-sequenced diatom species. These analyses revealed a number of diatom-specific genes that encode putative endoplasmic reticulum-targeting proteins. Significant numbers of these proteins showed homology to silicanin-1, which is a conserved diatom protein that reportedly contributes to cell wall formation. These proteins also included a previously unrecognized SET domain protein methyltransferase family that may regulate functions of cell wall formation-related proteins and long-chain polyamines. Proteomic analysis of cell wall-associated proteins in N. palea identified a protein that is also encoded by one of the diatom-specific genes. Expression analysis showed that candidate genes were upregulated in response to silicon, suggesting that these genes play roles in silica cell wall formation. These candidate genes can facilitate further investigations of silica cell wall formation in diatoms. Keywords Biomineralization . Diatom . Silica . Transcriptome . Proteome
Introduction Diatoms synthesize silica cell walls that have highly complex and elaborate nano-architectures. More than 100,000 diatom Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10126-020-09976-1) contains supplementary material, which is available to authorized users. * Michiko Nemoto [email protected] 1
Graduate School of Environmental and Life Science, Okayama University, Okayama 700-8530, Japan
2
Department of Biology, Tokyo Gakugei University, Tokyo 184-8511, Japan
species with differing species-specific morphologies have been identified (Round et al. 1990). The unique porous architectures of silica cell walls offer promise for the production of nextgeneration materials for various applications (Terracciano et al. 2018; Kroger and Brunner 2014). However, to exploit biomimetic silica materials obtained from diatoms, the molecular mechanisms of silica cell wall formation need to
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