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<p>Heterotrimeric G proteins are key components of signal transduction mediating growth, development, and stress responses in eukaryotes. Here, we identified and characterized a G protein α subunit gene (<i>SjGPA1</i>) from the economically important brown alga <i>Saccharina japonica</i> using genomic databases, molecular techniques, and bioinformatic analyses. <i>SjGPA1</i>, encoded by the nuclear genome, contains a 1,065&#xa0;bp open reading frame encoding 354 amino acids. The predicted protein has a molecular weight of 39.84&#xa0;kDa and an isoelectric point of 4.90, and exhibits the features of a stable, hydrophilic protein lacking signal peptides and transmembrane domains. SjGPA1 possesses the conserved functional domains typical of Gα proteins and is predicted to localize primarily to the cytoplasm and nucleus. Phylogenetic analysis shows that SjGPA1 clusters within a monophyletic clade of brown algae (Phaeophyceae), is most closely related to its ortholog from <i>Sargassum thunbergii</i> and forms a sister group with Gα proteins from <i>Undaria pinnatifida</i> and the model brown alga <i>Ectocarpus siliculosus</i>. Promoter analysis identified 22 cis-acting elements, including 9 growth-responsive, 2 hormone-responsive, 6 light-responsive, and 5 stress-responsive elements. Real-time quantitative PCR indicated that low salinity significantly upregulated SjGPA1 expression (3.52-fold), whereas high temperature caused no significant change, and no transcript was detected under high light, drought, or darkness. By contrast, Western blotting showed significantly reduced SjGPA1 protein levels under drought and darkness, and markedly suppressed accumulation under high temperature, low salinity, and high light. The purified recombinant SjGPA1 bound GTP but showed no detectable GTPase activity. Together, these results indicate complex post-transcriptional regulation and suggest that SjGPA1 contributes to the adaptation of <i>S. japonica</i> to marine environmental stresses, providing a basis for further functional analyses and molecular breeding for stress resistance.</p>

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Discovery and stress-responsive expression of the first G-protein α subunit in the cultivated kelp Saccharina japonica

  • 期刊论文

  • 发表日期：

    2026年2月26日

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  • Fang Lü,
  • Liuqing Tang,
  • Mengxue Xu,
  • Dongmei Zhan,
  • Haiyi Wu

摘要

Heterotrimeric G proteins are key components of signal transduction mediating growth, development, and stress responses in eukaryotes. Here, we identified and characterized a G protein α subunit gene (SjGPA1) from the economically important brown alga Saccharina japonica using genomic databases, molecular techniques, and bioinformatic analyses. SjGPA1, encoded by the nuclear genome, contains a 1,065 bp open reading frame encoding 354 amino acids. The predicted protein has a molecular weight of 39.84 kDa and an isoelectric point of 4.90, and exhibits the features of a stable, hydrophilic protein lacking signal peptides and transmembrane domains. SjGPA1 possesses the conserved functional domains typical of Gα proteins and is predicted to localize primarily to the cytoplasm and nucleus. Phylogenetic analysis shows that SjGPA1 clusters within a monophyletic clade of brown algae (Phaeophyceae), is most closely related to its ortholog from Sargassum thunbergii and forms a sister group with Gα proteins from Undaria pinnatifida and the model brown alga Ectocarpus siliculosus. Promoter analysis identified 22 cis-acting elements, including 9 growth-responsive, 2 hormone-responsive, 6 light-responsive, and 5 stress-responsive elements. Real-time quantitative PCR indicated that low salinity significantly upregulated SjGPA1 expression (3.52-fold), whereas high temperature caused no significant change, and no transcript was detected under high light, drought, or darkness. By contrast, Western blotting showed significantly reduced SjGPA1 protein levels under drought and darkness, and markedly suppressed accumulation under high temperature, low salinity, and high light. The purified recombinant SjGPA1 bound GTP but showed no detectable GTPase activity. Together, these results indicate complex post-transcriptional regulation and suggest that SjGPA1 contributes to the adaptation of S. japonica to marine environmental stresses, providing a basis for further functional analyses and molecular breeding for stress resistance.