Pierre Rouzé

We report the draft genome of the black cottonwood tree, Populus trichocarpa. Integration of shotgun sequence assembly with genetic mapping enabled chromosome-scale reconstruction of the genome. More than 45,000 putative protein-coding genes were identified. Analysis of the assembled genome revealed a whole-genome duplication event; about 8000 pairs of duplicated genes from that event survived in the Populus genome. A second, older duplication event is indistinguishably coincident with the divergence of the Populus and Arabidopsis lineages. Nucleotide substitution, tandem gene duplication, and gross chromosomal rearrangement appear to proceed substantially more slowly in Populus than in Arabidopsis. Populus has more protein-coding genes than Arabidopsis, ranging on average from 1.4 to 1.6 putative Populus homologs for each Arabidopsis gene. However, the relative frequency of protein domains in the two genomes is similar. Overrepresented exceptions in Populus include genes associated with lignocellulosic wall biosynthesis, meristem development, disease resistance, and metabolite transport.

The spider mite Tetranychus urticae is a cosmopolitan agricultural pest with an extensive host plant range and an extreme record of pesticide resistance. Here we present the completely sequenced and annotated spider mite genome, representing the first complete chelicerate genome. At 90 megabases T. urticae has the smallest sequenced arthropod genome. Compared with other arthropods, the spider mite genome shows unique changes in the hormonal environment and organization of the Hox complex, and also reveals evolutionary innovation of silk production. We find strong signatures of polyphagy and detoxification in gene families associated with feeding on different hosts and in new gene families acquired by lateral gene transfer. Deep transcriptome analysis of mites feeding on different plants shows how this pest responds to a changing host environment. The T. urticae genome thus offers new insights into arthropod evolution and plant–herbivore interactions, and provides unique opportunities for developing novel plant protection strategies. The genome of the spider mite Tetranychus urticae is sequenced, providing insights into its polyphagous feeding, silk production, hormonal repertoire and reduced Hox cluster. The spider mite (Tetranychus urticae) is a common agricultural pest that feeds on a wide range of hosts — including maize (corn), soya, tomatoes and peppers — and is notoriously resistant to pesticides. Its genome has now been sequenced and analysed, providing insights into its hormonal repertoire and the evolution of silk production. Transcriptome analysis of mites feeding on different plants reveals how this pest defends itself in a changing host environment and gives pointers to possible non-pesticide plant-protection strategies. The genome encodes 17 fibroin genes, and physical tests of spider-mite silk show it to be a natural nanomaterial with fibres that are more than 100 times thinner than those produced by silk spiders.

The fungus Laccaria bicolor — seen in its above-ground fruiting body presence as the 'bicoloured deceiver' mushroom — lives symbiotically on the roots of trees. Its genome has now been sequenced, and the key features of the genome characterized by transcript profiling. The study throws light on the mechanism of mycorrhizal symbiosis, the union of roots and soil fungi that is of vital important to plant productivity. And it will be of keen interest to evolutionary and plant biologists for its revelations about plant–fungus interactions shaping genomes over time. The genome of the fungus Laccaria bicolor is described; it is of keen interest to evolutionary and plant biologists for its revelations about plant–fungus interactions shaping genomes over time. Mycorrhizal symbioses—the union of roots and soil fungi—are universal in terrestrial ecosystems and may have been fundamental to land colonization by plants1,2. Boreal, temperate and montane forests all depend on ectomycorrhizae1. Identification of the primary factors that regulate symbiotic development and metabolic activity will therefore open the door to understanding the role of ectomycorrhizae in plant development and physiology, allowing the full ecological significance of this symbiosis to be explored. Here we report the genome sequence of the ectomycorrhizal basidiomycete Laccaria bicolor (Fig. 1) and highlight gene sets involved in rhizosphere colonization and symbiosis. This 65-megabase genome assembly contains ∼20,000 predicted protein-encoding genes and a very large number of transposons and repeated sequences. We detected unexpected genomic features, most notably a battery of effector-type small secreted proteins (SSPs) with unknown function, several of which are only expressed in symbiotic tissues. The most highly expressed SSP accumulates in the proliferating hyphae colonizing the host root. The ectomycorrhizae-specific SSPs probably have a decisive role in the establishment of the symbiosis. The unexpected observation that the genome of L. bicolor lacks carbohydrate-active enzymes involved in degradation of plant cell walls, but maintains the ability to degrade non-plant cell wall polysaccharides, reveals the dual saprotrophic and biotrophic lifestyle of the mycorrhizal fungus that enables it to grow within both soil and living plant roots. The predicted gene inventory of the L. bicolor genome, therefore, points to previously unknown mechanisms of symbiosis operating in biotrophic mycorrhizal fungi. The availability of this genome provides an unparalleled opportunity to develop a deeper understanding of the processes by which symbionts interact with plants within their ecosystem to perform vital functions in the carbon and nitrogen cycles that are fundamental to sustainable plant productivity.

The genome of Ectocarpus, a model organism for brown algae, has been sequenced. Brown algae are complex photosynthetic organisms that have adapted to life in rocky coastal environments. Genome analysis sheds light on this adaptation and reveals an extended set of light-harvesting and pigment biosynthesis genes and novel metabolic processes such as halide metabolism. Comparative genomic analyses highlight the likely importance of a family of receptor kinases and related molecules in the evolution of multicellularity in plants, animals and brown algae. The genome of Ectocarpus siliculosis, a model for the study of brown algae, has been sequenced. These seaweeds are complex photosynthetic organisms that have adapted to rocky coastal environments. Genome analysis sheds light on this adaptation, revealing an extended set of light-harvesting and pigment biosynthesis genes, and new metabolic processes such as halide metabolism. Comparative analyses are also significant with respect to the evolution of multicellularity in plants, animals and brown algae. Brown algae (Phaeophyceae) are complex photosynthetic organisms with a very different evolutionary history to green plants, to which they are only distantly related1. 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 algae2,3,4,5, closely related to the kelps6,7 (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 genetic2 approaches to explore these and other4,5 aspects of brown algal biology further.