The genome ofEctocarpus subulatus– a highly stress-tolerant brown alga

Abstract

35Brown algae are multicellular photosynthetic stramenopiles that colonize marine rocky shores 36 worldwide. Ectocarpus sp. Ec32 has been established as a genomic model for brown algae. Here we 37 present the genome and metabolic network of the closely related species, Ectocarpus subulatus 38Kützing, which is characterized by high abiotic stress tolerance. Since their separation, both strains 39show new traces of viral sequences and the activity of large retrotransposons, which may also be 40 related to the expansion of a family of chlorophyll-binding proteins. Further features suspected to 41 contribute to stress tolerance include an expanded family of heat shock proteins, the reduction of 42 genes involved in the production of halogenated defence compounds, and the presence of fewer cell 43wall polysaccharide-modifying enzymes. Overall, E. subulatus has mainly lost members of gene 44 families down-regulated in low salinities, and conserved those that were up-regulated in the same 45 condition. However, 96% of genes that differed between the two examined Ectocarpus species, as 46 well as all genes under positive selection, were found to encode proteins of unknown function. This 47 underlines the uniqueness of brown algal stress tolerance mechanisms as well as the significance of 48 establishing E. subulatus as a comparative model for future functional studies. 49 50 Organellar genomes 131 Plastid and mitochondrial genomes from E. subulatus have 95.5% and 91.5% sequence identity with 132 their Ectocarpus sp. Ec32 counterparts in the conserved regions respectively. Only minor structural 133 differences were observed between organellar genomes of both Ectocarpus genomes, as detailed in 134Supporting Information Text S1. 135

Revisiting australianectocarpus subulatus(phaeophyceae) from the hopkins river: distribution, abiotic environment, and associated microbiota

“…The species E. subulatus (Peters et al 2015) is related to the genomic model species Ectocarpus siliculosus (Cock et al 2010) and has been reported in highly variable environments with high levels of abiotic stressors, such temperature at Port Aransas, Texas, USA (Bolton 1983). More recently, the genome of E. subulatus has been sequenced, revealing that E. subulatu s, in comparison to Ectocarpus siliculosus , has lost members of gene families down-regulated in low salinities, and conserved those that were up-regulated (Dittami et al 2018, preprint). The E. subulatus strain from Hopkins River Falls has further been used for physiological experiments: it can grow in both seawater and fresh water and its transcriptomic and metabolic acclimation to these conditions has been examined (Dittami et al 2012) along with the composition of its cell wall with regard to sulfated polysaccharides (Torode et al 2015).…”

Biochemical characteristics of a diffusible factor that induces gametophyte to sporophyte switching in the brown alga Ectocarpus

“…The WSC domain family is one of the largest protein domain families in brown algae, with 444 members in Ectocarpus sp. strain Ec32 (Dittami et al 2020). Three of the 28 mannuronan C5-epimerase enzymes in Ectocarpus are predicted to possess WSC domains and, while their biochemical function has not been yet elucidated, these motifs may act as cell wall-binding domains, possibly targeting alginate (Michel et al 2010).…”

Changing microbial activities during low salinity acclimation in the brown algaEctocarpus subulatus

“…Raw sequencing reads were quality-trimmed with Trimmomatic (version 0.36, minimal Phred score: 20, minimal read length: 36 nucleotides) and aligned to the E. subulatus Bft15b reference genome (Dittami, Corre, et al, 2020) using STAR aligner version 2.6.0a (Dobin et al, 2013) to remove algal reads. Non-aligning (i.e.…”

“…Mutants of Arabidopsis and Cyanobacteria missing the last reaction of its biosynthetic pathway are viable but exhibit increased photosensitivity (Fatihi et al, 2015). In E. subulatus, just as in E. siliculosus, Saccharina latissima, and Cladosiphon okamuranus (Nègre et al, 2019;Dittami, Corre, et al, 2020), the last step of the vitamin K biosynthetic pathway is absent from the algal metabolic network. It suggests that these algae cannot produce vitamin K independently, although this compound has previously been detected in kelps (Yu et al, 2018).…”