192
S.M. Coelho et al.
projects has been increasing rapidly, and quite a large number of projects have been
recently completed or are nearing completion (Table 6.1, Fig. 6.2). To date, eight
algal genome sequences have been published. These are all from unicellular algae
and include six marine species, the diatoms Thalassiosira pseudonana (Armbrust
et al. 2004) and Phaeodactylum tricornutum (Bowler et al. 2008), two green prasinophyte algae Ostreococcus tauri (Derelle et al. 2006) and O. lucimarinus nomen
nudum (Palenik et al. 2007) and two Micromonas isolates (Worden et al. 2009),
plus two freshwater species, the red alga Cyanidioschyzon merolae (Matsuzaki et al.
2004) and the green alga Chlamydomonas reinhardtii (Merchant et al. 2007). Apart
from C. reinhardtii, which has quite a large genome (120 Mbp), these algae all
have small genomes, ranging from about 12 Mbp for Ostreococcus to 34 Mbp
for Thalassiosira. The following sections will look in detail at the application of
genomic approaches to specific marine microalgae, with a particular emphasis on
the diatom P. tricornutum and the prasinophyte O. tauri, which are being developed
as model organisms.
6.4.5.1 Diatom Genomics
The centric diatom T. pseudonana was the first marine microalga to be sequenced
(Armbrust et al. 2004). This phytoplankter is ecologically important and is distributed throughout the world’s oceans. Diatoms are heterokonts, and are therefore
only very distantly related to both animals and green plants. As a result, the genome
was found, rather surprisingly for a photosynthetic organism, to share characteristics with both of the latter groups. This was true both at the whole genome level and
in terms of specific metabolic processes. For example, Thalassiosira was found to
possess a complete urea cycle, a typical feature of animals.
The Thalassiosira genome sequence is now being exploited to investigate some
of the more exotic features of diatom biology. Many diatoms are able to build intricately patterned silica cell walls. The fabrication of these walls is of great interest
both as a biological process and because of potential nanotechnological applications. Recently, a whole genome tiling array approach was used to identify genes
Fig. 6.2 Some examples of marine algae for which genome sequencing projects have been carried out or are currently in process. (a) Ostreococcus sp., (b) Batycoccus sp. (photograph courtesy
of Marie-Josèphe Dinet), (c) Micromonassp. (from Guillou et al. 2004), (d) Emiliania huxleyi
(photograph courtesy of Jeremy R. Young, The Natural History Museum, London, UK), (e)
Guillardia theta (photograph courtesy of Geoff McFadden, University of Melbourne, Australia), (f)
Fragilariopsis cylindrus (photograph courtesy of Gerhard Dieckmann Alfred Wegener Institute for
Polar and Marine Research, Bremerhaven, Germany), (g) Thalassiosira pseudonana (photograph
courtesy of Virginia Armbrust, University of Washington, USA), (h) Phaeodactylum tricornutum (photograph courtesy of Alessandra De Martino and Chris Bowler, Ecole National Supérieur,
Paris, France), (i) Pseudo-nitzschia multiseries (photograph courtesy of the Joint Genome Institute,
USA), (j) detail of Ectocarpus siliculosus thallus showing release of meiospores from a unilocular sporangium. (k) Chondrus crispus plantlet (Photograph courtesy of Jonas Collén, Station
Biologique de Roscoff)
S.M. Coelho et al.
projects has been increasing rapidly, and quite a large number of projects have been
recently completed or are nearing completion (Table 6.1, Fig. 6.2). To date, eight
algal genome sequences have been published. These are all from unicellular algae
and include six marine species, the diatoms Thalassiosira pseudonana (Armbrust
et al. 2004) and Phaeodactylum tricornutum (Bowler et al. 2008), two green prasinophyte algae Ostreococcus tauri (Derelle et al. 2006) and O. lucimarinus nomen
nudum (Palenik et al. 2007) and two Micromonas isolates (Worden et al. 2009),
plus two freshwater species, the red alga Cyanidioschyzon merolae (Matsuzaki et al.
2004) and the green alga Chlamydomonas reinhardtii (Merchant et al. 2007). Apart
from C. reinhardtii, which has quite a large genome (120 Mbp), these algae all
have small genomes, ranging from about 12 Mbp for Ostreococcus to 34 Mbp
for Thalassiosira. The following sections will look in detail at the application of
genomic approaches to specific marine microalgae, with a particular emphasis on
the diatom P. tricornutum and the prasinophyte O. tauri, which are being developed
as model organisms.
6.4.5.1 Diatom Genomics
The centric diatom T. pseudonana was the first marine microalga to be sequenced
(Armbrust et al. 2004). This phytoplankter is ecologically important and is distributed throughout the world’s oceans. Diatoms are heterokonts, and are therefore
only very distantly related to both animals and green plants. As a result, the genome
was found, rather surprisingly for a photosynthetic organism, to share characteristics with both of the latter groups. This was true both at the whole genome level and
in terms of specific metabolic processes. For example, Thalassiosira was found to
possess a complete urea cycle, a typical feature of animals.
The Thalassiosira genome sequence is now being exploited to investigate some
of the more exotic features of diatom biology. Many diatoms are able to build intricately patterned silica cell walls. The fabrication of these walls is of great interest
both as a biological process and because of potential nanotechnological applications. Recently, a whole genome tiling array approach was used to identify genes
Fig. 6.2 Some examples of marine algae for which genome sequencing projects have been carried out or are currently in process. (a) Ostreococcus sp., (b) Batycoccus sp. (photograph courtesy
of Marie-Josèphe Dinet), (c) Micromonassp. (from Guillou et al. 2004), (d) Emiliania huxleyi
(photograph courtesy of Jeremy R. Young, The Natural History Museum, London, UK), (e)
Guillardia theta (photograph courtesy of Geoff McFadden, University of Melbourne, Australia), (f)
Fragilariopsis cylindrus (photograph courtesy of Gerhard Dieckmann Alfred Wegener Institute for
Polar and Marine Research, Bremerhaven, Germany), (g) Thalassiosira pseudonana (photograph
courtesy of Virginia Armbrust, University of Washington, USA), (h) Phaeodactylum tricornutum (photograph courtesy of Alessandra De Martino and Chris Bowler, Ecole National Supérieur,
Paris, France), (i) Pseudo-nitzschia multiseries (photograph courtesy of the Joint Genome Institute,
USA), (j) detail of Ectocarpus siliculosus thallus showing release of meiospores from a unilocular sporangium. (k) Chondrus crispus plantlet (Photograph courtesy of Jonas Collén, Station
Biologique de Roscoff)