Acclimation in photosynthetic organisms to light fluctuation. A, Route of treatments, methods, transcriptional and metabolic responses to severe light fluctuation and potential important TFs in P. tricornutum characterized in this work. Solid arrows link TFs and their known binding target genes. Dashed arrows link TFs and genes in the same WGCNA module. B, Schematic of adaptive plasticity to habitat light fields in terrestrial, freshwater, to marine photosynthetic organisms. The white ellipses with colorful edges depict crucial proteins responding to light fluctuation, including FLV (Allahverdiyeva et al., 2013; Gerotto et al., 2016; Yamamoto et al., 2016; Chaux et al., 2017; Jokel et al., 2018; Storti et al., 2018, 2020; Wada et al., 2018), PGR5 (Suorsa et al., 2012; 2013; Yamamoto et al., 2016; Yamori et al., 2016; Jokel et al., 2018; Yamamoto and Shikanai, 2019; ZHou et al., 2021), PGRL1 (Storti et al., 2018; Zhou et al., 2020), PGRL1-like protein Sll1217 (Dann and Leister, 2019), PGRL2 (Ruhle et al., 2021), STN7 (Tikkanen et al., 2010; Grieco et al., 2012), THIOREDOXINS (Nikkanen, 2018; Hou et al., 2021), plastidial terminal oxidase (Nawrocki et al., 2019), the respiratory terminal oxidases (Cyd: cytochrome bd-type quinol oxidase; Cox: aa3-type cytochrome c oxidase) (Lea-Smith et al., 2013; Grouneva et al., 2016), NDH (Yamori et al., 2016; Acuna et al., 2018; Storti et al., 2020), FCP (Tanabe et al., 2020), LHXSR (Gao et al., 2021), npq-mutants lacking LHCX1 (Bellan et al., 2020), or PSBS (Grieco et al., 2012; Gao et al., 2021), ion transporters and channels (Armbruster et al., 2014, 2016; Li et al., 2021), and chloroplast division proteins (Dutta et al., 2017). Black rectangles with colorful edges depict pathways influenced by light fluctuation enriched in proteomes of cyanobacteria (Mustila et al., 2021), chloroplast in diatom (Grouneva et al., 2016), and transcriptomes of cyanobacteria (Mustila et al., 2016; Riediger et al., 2019; Mustila et al., 2021), Arabidopsis (Jarvi et al., 2016; Schneider et al., 2019), tomato (Zhang et al., 2020), maize (Qu et al., 2021), and diatoms (this study). Dashed outline represents an ambiguous function under fluctuating light. White rectangles with gray edges represent key proteins or complex in the electron transport chain. The color of the edge corresponds to the color of the species name or treatment in this work. CL: constant light condition (80 μmol m⁻² s⁻¹); mFL: mildly fluctuating light condition (80–800 μmol m⁻² s⁻¹); sFL: severely fluctuating light condition (20–2,000 μmol m⁻² s⁻¹).