Plants are the foundation of terrestrial ecosystems and their colonization of land was likely facilitated by mutualistic associations with arbuscular mycorrhizal fungi. Following that founding event, plant diversification has led to the emergence of a tremendous diversity of mutualistic symbioses with microorganisms, ranging from extracellular associations to the most intimate intracellular associations, where fungal or bacterial symbionts are hosted inside plant cells. Through analysis of 271 transcriptomes and 122 plant genomes, we demonstrate that the common symbiosis signalling pathway controlling the association with arbuscular mycorrhizal fungi and with nitrogen-fixing bacteria specifically co-evolved with intracellular endosymbioses, including ericoid and orchid mycorrhizae in angiosperms and ericoid-like associations of bryophytes. In contrast, species forming exclusively extracellular symbioses like ectomycorrhizae or associations with cyanobacteria have lost this signalling pathway. This work unifies intracellular symbioses, revealing conservation in their evolution across 450 million years of plant diversification.

The complete genome sequence of a Newcastle disease virus (NDV) isolated from a chicken in Sweden was determined and compared with other NDV sequences. The isolate was shown to belong to genotype VIIb, which arose in the Far East and spread around the world during the 1990s. It had a length of 15,192 bases and consisted of six genes in the order 3'-NP-P-M-F-HN-L-5'. The F protein cleavage site was 112-RRQRRF-117, corresponding to that of a virulent pathotype.

Hepatitis E virus (HEV) has been detected in humans and in a broad range of animals, including pigs. For the first time the full-length genomic sequence of a HEV of European porcine origin, termed swX07-E1, was determined. Comparative analysis of 76 complete or nearly complete nucleotide sequences showed that swX07-E1 shares the highest nucleotide identity with Japanese swine HEV swJ8-5 and swJ12-4. The whole-genome phylogenetic analysis showed that swX07-E1 from Europe belongs to genotype-3 HEV, clusters with variants from Japan, Mongolia and Kyrgyzstan in subgroup 3c, but it is divergent from the prototype US HEV. Our analysis indicates that swX07-E1 represents a new subgroup of genotype-3 and that analysis of full-length sequences is necessary to discover new subgroups of HEV. According to our knowledge, swX07-E1 is the first full-length genome sequence of HEV from European swine. Knowledge about the full length HEV sequence from European swine is very important for understanding the HEV evolutionary events and the molecular mechanism of infection in human and in animals.

Plants are the foundation of terrestrial ecosystems and their colonization of land was facilitated by mutualistic associations with arbuscular mycorrhizal fungi. Following that founding event, plant diversification has led to the emergence of a tremendous diversity of mutualistic symbioses with microorganisms, ranging from extracellular associations to the most intimate intracellular associations, where fungal or bacterial symbionts are hosted inside plant cells. Through analysis of 271 transcriptomes and 122 plant genomes, we demonstrate that the common symbiosis signalling pathway controlling the association with arbuscular mycorrhizal fungi and with nitrogen-fixing bacteria specifically co-evolved with intracellular endosymbioses, including ericoid and orchid mycorrhizae in angiosperms and ericoid-like associations of bryophytes. In contrast, species forming exclusively extracellular symbioses like ectomycorrhizae or associations with cyanobacteria have lost this signalling pathway. This work unifies intracellular symbioses, revealing conservation in their evolution across 450 million years of plant diversification. Introductory paragraphSince they colonized land 450 million years ago, plants have been the foundation of most terrestrial ecosystems 1 . Such successful colonization occurred only once in the plant kingdom and was supported by the symbiotic association formed with arbuscular mycorrhizal fungi 2,3 . Following that founding event, plant diversification was accompanied by the emergence of alternative or additional symbionts 4 . Among alternative symbioses, the association between orchids and basidiomycetes and between Ericales and ascomycetes or basidiomycetes are two endosymbioses with specific intracellular structures in two plant lineages that lost the ability to form the Arbuscular Mycorrhizal Symbiosis (AMS) 5 . As such, orchid mycorrhiza and ericoid-mycorrhiza represent two clear symbiosis switches, whereby intracellular associations are sustained, but the nature of the symbionts are radically different. Similarly, within the liverworts, the Jungermanniales engage in ericoid-like endosymbioses but not AM symbiosis and represent another symbiont switch that occurred during plant evolution 6 . Other symbioses can occur simultaneously with AMS, for example the root nodule symbiosis, an association with nitrogen-fixing bacteria that evolved in the last common ancestor of Fabales, Fagales, Cucurbitales and Rosales 7 . Another example is ectomycorrhizae, an extracellular symbiosis found in several gymnosperm and angiosperm lineages: in some lineages both AMS and ectomycorrhizae have been retained; while other lineages have switched from AMS to ectomycorrhizae 8 . Finally, associations with cyanobacteria, which occur only in the intercellular spaces of the plant tissue, can be found in diverse species within the embryophytes, in hornworts, liverworts, ferns, gymnosperms and angiosperms 9 . Despite the improved nutrient acquisition afforded to plants by these different types of mutualistic symbioses, e...