Genomics of brown algae: current advances and future prospects

Exploring Core Response Mechanisms to Multiple Environmental Stressors Via A Genome-Wide Study in the Brown Alga Saccharina japonica (Laminariales, Phaeophyceae)

Saccharina japonica is an important large brown alga and a major component of productive beds on the northwest coast of the Pacific Ocean. Abiotic stress response mechanisms are receiving considerable attention because global climate change is increasing their abiotic stress levels. However, our knowledge of how S. japonica broadly responds to stress is limited. In this study, we investigated the S. japonica responsive genes underlying acclimation to diverse stressors of acidification, high light, high temperature, hypersalinity, and hyposalinity and identified 408 core genes constantly and differentially expressed in response to all stressors. Our results confirm that stressors had strong effects on genes participating in photosynthesis, amino acid metabolism, carbohydrate metabolism, halogen metabolism, and reactive oxygen species defense. These findings will improve our understanding of brown algal response mechanisms linked to environmental stress and provide a list of candidate genes for improving algal stress tolerance in light of environmental stress in future studies.

Infection of the brown alga Ectocarpus siliculosus by the oomycete Eurychasma dicksonii induces oxidative stress and halogen metabolism

Pathogens are increasingly being recognized as key evolutionary and ecological drivers in marine ecosystems. Defence mechanisms of seaweeds, however, have mostly been investigated by mimicking infection using elicitors. We have established an experimental pathosystem between the genome brown model seaweed Ectocarpus siliculosus and the oomycete Eurychasma dicksonii as a powerful new tool to investigate algal responses to infection. Using proteomics, we identified 21 algal proteins differentially accumulated in response to Eu. dicksonii infection. These include classical algal stress response proteins such as a manganese superoxide dismutase, heat shock proteins 70 and a vanadium bromoperoxidase. Transcriptional profiling by qPCR confirmed the induction of the latter during infection. The accumulation of hydrogen peroxide was observed at different infection stages via histochemical staining. Inhibitor studies confirmed that the main source of hydrogen peroxide is superoxide converted by superoxide dismutase. Our data give an unprecedented global overview of brown algal responses to pathogen infection, and highlight the importance of oxidative stress and halogen metabolism in these interactions. This suggests overlapping defence pathways with herbivores and abiotic stresses. We also identify previously unreported actors, in particular a Rad23 and a plastid-lipid-associated protein, providing novel insights into the infection and defence processes in brown algae.

Ecological and evolutionary genomics of marine photosynthetic organisms

Environmental (ecological) genomics aims to understand the genetic basis of relationships between organisms and their abiotic and biotic environments. It is a rapidly progressing field of research largely due to recent advances in the speed and volume of genomic data being produced by next generation sequencing (NGS) technologies. Building on information generated by NGS-based approaches, functional genomic methodologies are being applied to identify and characterize genes and gene systems of both environmental and evolutionary relevance. Marine photosynthetic organisms (MPOs) were poorly represented amongst the early genomic models, but this situation is changing rapidly. Here we provide an overview of the recent advances in the application of ecological genomic approaches to both prokaryotic and eukaryotic MPOs. We describe how these approaches are being used to explore the biology and ecology of marine cyanobacteria and algae, particularly with regard to their functions in a broad range of marine ecosystems. Specifically, we review the ecological and evolutionary insights gained from whole genome and transcriptome sequencing projects applied to MPOs and illustrate how their genomes are yielding information on the specific features of these organisms.