200
S.M. Coelho et al.
fucoid seaweeds of the intertidal zone and the large kelps that form forests in the
subtidal zone. Historically, research on brown algae has been focused, to a large
degree, on these two groups. This is not only because of their ecological importance but also either because they have important industrial applications (for the
kelps; McHugh 2003, Bartsch et al. 2008) or because they have been developed as
models for fundamental research (for the Fucales, see below). As far as genomic
analysis of these two orders of seaweeds is concerned, a collection of nearly 3,000
ESTs has been generated for Laminaria digitata, including sequences from genes
expressed during the sporophyte and gametophyte generations of the life cycle
(Crépineau et al. 2000) and in sporophyte-derived protoplasts (Roeder et al. 2005).
These sequences have allowed access to genes involved in a number of different
processes including carbon-concentrating mechanisms, cell wall biosynthesis, halogen metabolism and stress responses. In contrast, EST sequences have only very
recently been established for fucoid seaweeds (Gareth Pearson, CCMAR Faro, personal communication) despite the fact that this group has been used extensively to
characterise events during early embryogenesis (Berger et al. 1994, Bouget et al.
1998, Corellou et al. 2000, Goddard et al. 2000, Corellou et al. 2001, Coelho et al.
2002) and are well characterised in terms of their ecology (Serrao et al. 1996, Coyer
et al. 2007, Muhlin et al. 2008).
Although EST approaches are providing insights into the biology the
Laminariales and Fucales groups, at the present time these organisms are not appropriate models for more extensive genomic approaches such as genome sequencing
or gene function analysis. There are two main reasons for this. Firstly, both groups
consist of organisms with large genomes (e.g. 650 Mbp for Laminaria digitata and
1095 Mbp for Fucus serratus; Le Gall et al. 1993, Peters et al. 2004). Secondly,
they are large organisms with long life cycles, and this limits the scope for laboratory experimentation. In response to these limitations, a search was recently carried
out for a model organism from within the brown algae that would be better adapted
for genomic analysis. This search led to the selection of the filamentous brown alga
Ectocarpus siliculosus (Peters et al. 2004).
Ectocarpus siliculosus is a member of the Ectocarpales, which has recently been
shown to be among the most evolved of the brown algal orders, closely related to
the kelps. Ectocarpus has been studied in the laboratory since the nineteenth century (see Charrier et al. 2008 and references therein). Early research included the
description of the species followed by studies of its reproductive biology and life history. Other aspects that have been investigated include ultrastructure, photosynthesis
and carbon uptake, pheromone production, gamete recognition and interactions with
pathogens, in particular with the virus EsV-1 which integrates into the genome of
this alga following infection.
The choice to develop Ectocarpus as a model organism for the brown algae was
based on a number of features that make it well adapted for the application of both
genomic and genetic approaches. One particularly important factor was the size of
its genome, which at 200 Mbp is significantly smaller than those of kelps and fucoid
brown algae. It also has several features that make it well adapted to laboratory work,
including its small size, the fact that the life cycle can be completed in Petri dishes
S.M. Coelho et al.
fucoid seaweeds of the intertidal zone and the large kelps that form forests in the
subtidal zone. Historically, research on brown algae has been focused, to a large
degree, on these two groups. This is not only because of their ecological importance but also either because they have important industrial applications (for the
kelps; McHugh 2003, Bartsch et al. 2008) or because they have been developed as
models for fundamental research (for the Fucales, see below). As far as genomic
analysis of these two orders of seaweeds is concerned, a collection of nearly 3,000
ESTs has been generated for Laminaria digitata, including sequences from genes
expressed during the sporophyte and gametophyte generations of the life cycle
(Crépineau et al. 2000) and in sporophyte-derived protoplasts (Roeder et al. 2005).
These sequences have allowed access to genes involved in a number of different
processes including carbon-concentrating mechanisms, cell wall biosynthesis, halogen metabolism and stress responses. In contrast, EST sequences have only very
recently been established for fucoid seaweeds (Gareth Pearson, CCMAR Faro, personal communication) despite the fact that this group has been used extensively to
characterise events during early embryogenesis (Berger et al. 1994, Bouget et al.
1998, Corellou et al. 2000, Goddard et al. 2000, Corellou et al. 2001, Coelho et al.
2002) and are well characterised in terms of their ecology (Serrao et al. 1996, Coyer
et al. 2007, Muhlin et al. 2008).
Although EST approaches are providing insights into the biology the
Laminariales and Fucales groups, at the present time these organisms are not appropriate models for more extensive genomic approaches such as genome sequencing
or gene function analysis. There are two main reasons for this. Firstly, both groups
consist of organisms with large genomes (e.g. 650 Mbp for Laminaria digitata and
1095 Mbp for Fucus serratus; Le Gall et al. 1993, Peters et al. 2004). Secondly,
they are large organisms with long life cycles, and this limits the scope for laboratory experimentation. In response to these limitations, a search was recently carried
out for a model organism from within the brown algae that would be better adapted
for genomic analysis. This search led to the selection of the filamentous brown alga
Ectocarpus siliculosus (Peters et al. 2004).
Ectocarpus siliculosus is a member of the Ectocarpales, which has recently been
shown to be among the most evolved of the brown algal orders, closely related to
the kelps. Ectocarpus has been studied in the laboratory since the nineteenth century (see Charrier et al. 2008 and references therein). Early research included the
description of the species followed by studies of its reproductive biology and life history. Other aspects that have been investigated include ultrastructure, photosynthesis
and carbon uptake, pheromone production, gamete recognition and interactions with
pathogens, in particular with the virus EsV-1 which integrates into the genome of
this alga following infection.
The choice to develop Ectocarpus as a model organism for the brown algae was
based on a number of features that make it well adapted for the application of both
genomic and genetic approaches. One particularly important factor was the size of
its genome, which at 200 Mbp is significantly smaller than those of kelps and fucoid
brown algae. It also has several features that make it well adapted to laboratory work,
including its small size, the fact that the life cycle can be completed in Petri dishes