A rapid aureochrome opto-switch enables diatom acclimation to dynamic light.

Diatoms often outnumber other eukaryotic algae in the oceans, especially in coastal environments characterized by frequent fluctuations in light intensity. The identities and operational mechanisms of regulatory factors governing diatom acclimation to high light stress remain largely elusive. Here, we identified the AUREO1c protein from the coastal diatom Phaeodactylum tricornutum as a crucial regulator of non-photochemical quenching (NPQ), a photoprotective mechanism that dissipates excess energy as heat. AUREO1c detects light stress using a light-oxygen-voltage (LOV) domain and directly activates the expression of target genes, including LI818 genes that encode NPQ effector proteins, via its bZIP DNA-binding domain. In comparison to a kinase-mediated pathway reported in the freshwater green alga Chlamydomonas reinhardtii, the AUREO1c pathway exhibits a faster response and enables accumulation of LI818 transcript and protein levels to comparable degrees between continuous high-light and fluctuating-light treatments. We propose that the AUREO1c-LI818 pathway contributes to the resilience of diatoms under dynamic light conditions.

Phylogeny and genetic variations of the three genome compartments in haptophytes shed light on the rapid evolution of coccolithophores.

Haptophyte algae, including coccolithophores, play key roles in global carbon cycling and ecosystem. They exhibit exceptional morphological and functional diversity. However, their phylogeny is mostly based on short markers and genome researches are always limited to few species, hindering a better understanding about their evolution and diversification. In this study, by assembling 69 new plastid genomes, 65 new mitochondrial genomes, and 55 nuclear drafts, we systematically analyzed their genome variations and built the most comprehensive phylogenies in haptophytes and Noelaerhabdaceae, with the latter is the family of the model coccolithophore Emiliania huxleyi. The haptophyte genomes vary significantly in size, gene content, and structure. We detected phylogenetic incongruence of Prymnesiales between genome compartments. In Noelaerhabdaceae, by including Reticulofenestra sessilis and a proper outgroup, we found R. sessilis was not the basal taxon of this family. Noelaerhabdaceae strains have very similar genomic features and conserved sequences, but different gene content and dynamic structure. We speculate that was caused by DNA double-strand break repairs. Our results provide valuable genetic resources and new insights into the evolution of haptophytes, especially coccolithophores.

Growth and antioxidant production of Spirulina in different NaCl concentrations.

OBJECTIVE: To evaluate the quantity of Spirulina cultured in seawater, salt-tolerant strains were screened out and their growth and antioxidant accumulation were studied in different salt concentrations RESULTS: Salt tolerance of five Spirulina strains were investigated with modified Zarrouk medium (with 200-800 mM NaCl). All strains grew well with 400 mM NaCl; their growth rates were almost same as in the control medium. Spirulina strains FACHB-843 (SP843) and FACHB-972 (SP972) had the highest salt tolerance their growth rates in 600 mM NaCl were nearly same as the control. Both strains produced more carotene, phycocyanin, polysaccharides, proline and betaine in 400-600 mM NaCl than the control. Salt stress also induced them to produce higher activities of superoxide dismutase and peroxidase. Total antioxidant capacities of SP843 and SP972 peaked at 600 and 400 mM NaCl, respectively. CONCLUSION: Spirulina strains cultured with seawater accumulate more bioactive substances and will have a higher nutritive value.