The global dynamic of DNA methylation in response to heat stress revealed epigenetic mechanism of heat acclimation in Saccharina japonica.

Saccharina japonica is an ecologically and economically important kelp in cold-temperate regions. When it is cultivated on a large scale in the temperate and even subtropical zones, heat stress is a frequent abiotic stress. This study is the first attempt to reveal the regulatory mechanism of the response to heat stress from the perspective of DNA methylation in S. japonica. We firstly obtained the characteristics of variation in the methylome under heat stress, and observed that heat stress caused a slight increase in the overall methylation level and methylation rate, especially in the non-coding regions of the genome. Secondly, we noted that methylation was probably one of factors affecting the expression of genes, and that methylation within the gene body was positively correlated with the gene expression (rho = 0.0784). Moreover, it was found that among the differentially expressed genes regulated by methylation, many genes were related to heat stress response, such as HSP gene family, genes of antioxidant enzymes, genes related to proteasome-ubiquitination pathway, and plant cell signaling pathways. This study demonstrated that DNA methylation is involved in regulating the response to heat stress, laying a foundation for studying the acclimation and adaptation of S. japonica to heat stress from an epigenetic perspective.

Genome-Wide Identification and Analysis of the Aureochrome Gene Family in Saccharina japonica and a Comparative Analysis with Six Other Algae.

Aureochrome (AUREO) is a kind of blue light photoreceptor with both LOV and bZIP structural domains, identified only in Stramenopiles. It functions as a transcription factor that responds to blue light, playing diverse roles in the growth, development, and reproduction of Stramenopiles. Most of its functions are currently unknown, especially in the economically important alga S. japonica farmed on a large scale. This study provided a comprehensive analysis of the characteristics of AUREO gene families in seven algae, focusing on the AUREOs of S. japonica. AUREO genes were strictly identified from seven algal genomes. Then AUREO phylogenetic tree was constructed from 44 conserved AUREO genes collected. These AUREO genes were divided into five groups based on phylogenetic relationships. A total of 28 genes unnamed previously were named according to the phylogenetic tree. A large number of different cis-acting elements, especially bZIP transcription factors, were discovered upstream of AUREO genes in brown algae. Different intron/exon structural patterns were identified among all AUREOs. Transcriptomic data indicated that the expression of Sj AUREO varied significantly during the different development stages of S. japonica gametophytes. Periodic rhythms of light induction experiments indicate that Sj AUREO existed in a light-dependent circadian expression pattern, differing from other similar studies in the past. This may indicate that blue light affects gametophyte development through AUREO as a light signal receptor. This study systematically identified and analyzed the AUREO gene family in seven representative brown algae, which lay a good foundation for further study and understanding of AUERO functions in agal growth and development.