The Ectocarpus genome and the independent evolution of multicellularity in brown algae

Abstract

Brown algae (Phaeophyceae) are complex photosynthetic organisms with a very different evolutionary history to green plants, to which they are only distantly related(1). These seaweeds are the dominant species in rocky coastal ecosystems and they exhibit many interesting adaptations to these, often harsh, environments. Brown algae are also one of only a small number of eukaryotic lineages that have evolved complex multicellularity (Fig. 1). We report the 214 million base pair (Mbp) genome sequence of the filamentous seaweed Ectocarpus siliculosus (Dillwyn) Lyngbye, a model organism for brown algae(2-5), closely related to the kelps(6,7) (Fig. 1). Genome features such as the presence of an extended set of light-harvesting and pigment biosynthesis genes and new metabolic processes such as halide metabolism help explain the ability of this organism to cope with the highly variable tidal environment. The evolution of multicellularity in this lineage is correlated with the presence of a rich array of signal transduction genes. Of particular interest is the presence of a family of receptor kinases, as the independent evolution of related molecules has been linked with the emergence of multicellularity in both the animal and green plant lineages. The Ectocarpus genome sequence represents an important step towards developing this organism as a model species, providing the possibility to combine genomic and genetic(2) approaches to explore these and other(4,5) aspects of brown algal biology further

Finding a partner in the ocean: molecular and evolutionary bases of the response to sexual cues in a planktonic diatom

“…Of the known classes of repetitive elements, LTR retrotransposons were the most abundant group of annotated repeats (6%) (Fig. S3a–c), similar to previous reports in other diatoms (Maumus et al ., 2009), as well as other Stramenopiles (Cock et al ., 2010; Ye et al ., 2015), yeast (Bleykasten‐Grosshans & Neuvéglise, 2011) and some flowering plants (Bennetzen, 2005). To investigate the role of LTRs in shaping the genomic structure of P. multistriata , a de novo search specific for complete LTR elements was performed in the genomes of five diatoms and that of Oryza sativa .…”

“…The genome size, N50 value and GC content were taken from the respective publications (Armbrust et al ., 2004; Bowler et al ., 2008; Cock et al ., 2010; Lévesque et al ., 2010; Lommer et al ., 2012; Tanaka et al ., 2015; Mock et al ., 2017). …”

Profiling of the transcriptome of Porphyra yezoensis with Solexa sequencing technology

“…Flavonoids are another group of compounds thought to protect against ultraviolet radiation in terrestrial plants [37]. A pathway of flavonoid biosynthesis including many homologues genes related to the terrestrial plant was identified in P. yezoensis, and this pathway was also found in Ectocarpus but was completely absent from diatom or green algal genomes [38]. It was worth noting that LI818 family proteins, the light-stress related LHCs, were failed to be identified in the pool of unigenes.…”

Analysis of Light-Dependent Cell Morphology and an Accumulation Response in <i>Ochromonas danica</i>

“…Some GL responses, although less effective than BL or RL, have already been reported to have a role in morphogenesis in the brown alga, Scytosiphon lomentaria (Dring and Lüning 1975) and in chloroplast movement in the centric diatom, Pleurosira laevis (Furukawa et al 1998). Recently, genome analysis of 2 diatom species, Thalassiosira pseudonana and Phaeodactylum tricornatum, and 1 brown alga, Ectocarpus siliculosis, revealed that they conserve many BL receptors, such as cryptochromes, LOV-histidine kinases and aureochromes, or the chromophore binding domain of phytochrome, GAF domain (Armbrust et al 2004, Bowler et al 2008, Cock et al 2010. However, the well-known GL receptor rhodopsin was missing from these genomes.…”