Sandra Heinrich

Transcriptomic Analysis of Acclimation to Temperature and Light Stress in Saccharina latissima (Phaeophyceae)

Kelps, brown algae of the order Laminariales, dominate rocky shores and form huge kelp beds which provide habitat and nurseries for various marine organisms. Whereas the basic physiological and ecophysiological characteristics of kelps are well studied, the molecular processes underlying acclimation to different light and temperature conditions are still poorly understood. Therefore we investigated the molecular mechanisms underlying the physiological acclimation to light and temperature stress. Sporophytes of S. latissima were exposed to combinations of light intensities and temperatures, and microarray hybridizations were performed to determine changes in gene expression patterns. This first large-scale transcriptomic study of a kelp species shows that S. latissima responds to temperature and light stress with a multitude of transcriptional changes: up to 32% of genes showed an altered expression after the exposure experiments. High temperature had stronger effects on gene expression in S. latissima than low temperature, reflected by the higher number of temperature-responsive genes. We gained insights into underlying molecular processes of acclimation, which includes adjustment of the primary metabolism as well as induction of several ROS scavengers and a sophisticated regulation of Hsps. We show that S. latissima, as a cold adapted species, must make stronger efforts for acclimating to high than to low temperatures. The strongest response was caused by the combination of high temperatures with high light intensities, which proved most harmful for the alga.

Temperature and light interactively modulate gene expression in Saccharina latissima (Phaeophyceae).

Macroalgae of the order Laminariales (kelp) are important components of cold‐temperate coastal ecosystems. Major factors influencing their distribution are light (including UV radiation) and temperature. Therefore, future global environmental changes potentially will impact their zonation, distribution patterns, and primary productivity. Many physiological studies were performed on UV radiation and temperature stress in kelp but combinatory effects have not been analyzed and so far no study is available on the molecular processes involved in acclimation to these stresses. Therefore, sporophytes of Saccharina latissima were exposed for 2 weeks to 12 combinations of photosynthetically active radiation (PAR), UV radiation and temperature. Subsequently, microarray hybridizations were performed to determine changes in gene expression patterns. Several effects on the transcriptome were observed after exposure experiments. The strongest effect of temperature on gene expression was observed at 2°C. Furthermore, UV radiation had stronger effects on gene expression than high PAR, and caused stronger induction genes correlated with categories such as photosynthetic components and vitamin B6 biosynthesis. Higher temperatures ameliorated the negative effects of UV radiation in S. latissima. Regulation of reactive oxygen species (ROS) scavenging seems to work in a compartment specific way. Gene expression profiles of ROS scavengers indicated a high amount of oxidative stress in response to the 2°C condition as well as to excessive light at 12°C. Interestingly, stress levels that did not lead to physiological alterations already caused by a transcriptomic response.

A comprehensive cDNA library of light- and temperature-stressed Saccharina latissima (Phaeophyceae)

Macroalgae of the order Laminariales (kelps) are important marine coastal primary producers with prime significance for ecosystem function. Important factors influencing their distribution include light and temperature but the molecular basis of kelp responses to these factors is poorly understood. We therefore constructed a comprehensive cDNA library from RNA sampled under various light and temperature regimes, as a basis for future studies about the mechanisms and pathways involved in acclimation to light and temperature stress in Saccharina latissima. A total of 400 503 ESTs was assembled into 28 803 contigs. We were able to assign putative functions or orthology relationships to more than 10 000 contigs by BLASTx, Interpro protein-motif annotation, or Gene Ontology (GO). The most frequent Interpro protein domains found in the cDNA library were the protein kinase-like domain, serine/threonine-protein kinase-like domain, and NAD(P)-binding and thioredoxin-like fold domain. Enzyme code (EC) annotation yielded attributions for 480 contigs, providing a total of 625 ECs, which could be mapped to 85 biochemical pathways. Comparative genomics of S. latissima and Ectocarpus siliculosus indicated that our cDNA library gave a genome coverage of approximately 70%, assuming similar gene numbers in both species. GO term occurrence in S. latissima and E. siliculosus showed a similar distribution pattern among the root ontologies biological process, molecular function and cellular component. Comparative protein domain annotation of S. latissima und E. siliculosus showed that, probably due to the chosen stress conditions, the domains ‘thioredoxin fold’, ‘thioredoxin-like fold’, ‘heat shock protein 70’, and ‘bromoperoxidase/chloroperoxidase C-terminal’ are over-represented in the cDNA library.