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<p>Previous findings revealed strain-specific differences in pigment composition, photoprotective capacity, and photosynthetic efficiency among <i>Raphidiopsis raciborskii</i> strains. To complement these results, the present study examined four strains, three non-cylindrospermopsin-producing isolates from temperate regions in Poland and one strain from tropical Australia that produces this cyanotoxin, in order to elucidate acclimation mechanisms under combined chill/light stress using functional and molecular approaches. The investigation focused on photosystem II (PSII) performance and the expression of genes involved in transcriptional and translational regulation (<i>rbp1, nusG</i>), membrane remodelling (<i>desA</i>), photosynthetic function (<i>ccr2</i>), PSII repair (<i>ftsH, fabZ</i>), and compatible solute synthesis (<i>asd</i>). By combining JIP test analysis with gene expression profiling, the study integrates functional and transcriptional perspectives to better understand how <i>R. raciborskii</i> adjusts its photosynthetic machinery to environmental stress. JIP test analysis revealed distinct photosynthetic responses among strains under combined chill/light stress. Temperate strains exhibited increased energy dissipation (DI₀/RC) and activation of cyclic electron flow, enhancing photoprotection and PSII stability. The strain UAM/DH-MRr showed simultaneous enhancement of linear and cyclic electron transport, indicating flexible energy redistribution. Gene expression profiling demonstrated ecotype-specific acclimation strategies. Early activation of transcriptional regulators (<i>nusG, rpb1</i>) was followed by the induction of membrane remodelling (<i>desA</i>), PSII repair (<i>ftsH, fabZ</i>), and compatible solute synthesis (<i>asd</i>). The tropical strain CS-506 displayed the most extensive and sustained transcriptional response, while temperate strains showed rapid or delayed activation. The weakest response in UAM/DH-MRr suggested tolerance or pre-adaptation. Overall, these results highlight flexible, strain-dependent acclimation mechanisms that underpin the ecological success and climatic adaptability of <i>R. raciborskii.</i></p>

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Regulation of photosystem II and key stress-response genes in Raphidiopsis raciborskii under combined chill/light stress

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月3日

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  • Nada Tokodi,
  • Adam Antosiak,
  • Damjana Drobac Backović,
  • Dariusz Dziga

摘要

Previous findings revealed strain-specific differences in pigment composition, photoprotective capacity, and photosynthetic efficiency among Raphidiopsis raciborskii strains. To complement these results, the present study examined four strains, three non-cylindrospermopsin-producing isolates from temperate regions in Poland and one strain from tropical Australia that produces this cyanotoxin, in order to elucidate acclimation mechanisms under combined chill/light stress using functional and molecular approaches. The investigation focused on photosystem II (PSII) performance and the expression of genes involved in transcriptional and translational regulation (rbp1, nusG), membrane remodelling (desA), photosynthetic function (ccr2), PSII repair (ftsH, fabZ), and compatible solute synthesis (asd). By combining JIP test analysis with gene expression profiling, the study integrates functional and transcriptional perspectives to better understand how R. raciborskii adjusts its photosynthetic machinery to environmental stress. JIP test analysis revealed distinct photosynthetic responses among strains under combined chill/light stress. Temperate strains exhibited increased energy dissipation (DI₀/RC) and activation of cyclic electron flow, enhancing photoprotection and PSII stability. The strain UAM/DH-MRr showed simultaneous enhancement of linear and cyclic electron transport, indicating flexible energy redistribution. Gene expression profiling demonstrated ecotype-specific acclimation strategies. Early activation of transcriptional regulators (nusG, rpb1) was followed by the induction of membrane remodelling (desA), PSII repair (ftsH, fabZ), and compatible solute synthesis (asd). The tropical strain CS-506 displayed the most extensive and sustained transcriptional response, while temperate strains showed rapid or delayed activation. The weakest response in UAM/DH-MRr suggested tolerance or pre-adaptation. Overall, these results highlight flexible, strain-dependent acclimation mechanisms that underpin the ecological success and climatic adaptability of R. raciborskii.