Novel Sex Cells and Evidence for Sex Pheromones in Diatoms

BACKGROUND: Diatoms belong to the stramenopiles, one of the largest groups of eukaryotes, which are primarily characterized by a presence of an anterior flagellum with tubular mastigonemes and usually a second, smooth flagellum. Based on cell wall morphology, diatoms have historically been divided into centrics and pennates, of which only the former have flagella and only on the sperm. Molecular phylogenies show the pennates to have evolved from among the centrics. However, the timing of flagellum loss--whether before the evolution of the pennate lineage or after--is unknown, because sexual reproduction has been so little studied in the 'araphid' basal pennate lineages, to which Pseudostaurosira belongs. METHODS/PRINCIPAL FINDING: Sexual reproduction of an araphid pennate, Pseudostaurosira trainorii, was studied with light microscopy (including time lapse observations and immunofluorescence staining observed under confocal scanning laser microscopy) and SEM. We show that the species produces motile male gametes. Motility is mostly associated with the extrusion and retrieval of microtubule-based 'threads', which are structures hitherto unknown in stramenopiles, their number varying from one to three per cell. We also report experimental evidence for sex pheromones that reciprocally stimulate sexualization of compatible clones and orientate motility of the male gametes after an initial 'random walk'. CONCLUSIONS/SIGNIFICANCE: The threads superficially resemble flagella, in that both are produced by male gametes and contain microtubules. However, one striking difference is that threads cannot beat or undulate and have no motility of their own, and they do not bear mastigonemes. Threads are sticky and catch and draw objects, including eggs. The motility conferred by the threads is probably crucial for sexual reproduction of P. trainorii, because this diatom is non-motile in its vegetative stage but obligately outbreeding. Our pheromone experiments are the first studies in which gametogenesis has been induced in diatoms by cell-free exudates, opening new possibilities for molecular 'dissection' of sexualization

Analysis of Expressed Sequence Tags from the Marine Microalga Pseudochattonella farcimen (Dictyochophyceae)

Pseudochattonella farcimen (Eikrem, Edvardsen, et Throndsen) is a unicellular alga belonging to the Dictyochophyceae (Heterokonta). It forms recurring blooms in Scandinavian coastal waters, and has been associated to fish mortality. Here we report the sequencing and analysis of 10,368 expressed sequence tags (ESTs) corresponding to 8,149 unique gene models from this species. Compared to EST libraries from other heterokonts, P. farcimen contains a high number of genes with functions related to cell communication and signaling. We found several genes encoding proteins related to fatty acid metabolism, including eight fatty acid desaturases and two phospholipase A2 genes. Three desaturases are highly similar to 4-desaturases from haptophytes. P. farcimen also possesses three putative polyketide synthases (PKSs), belonging to two different families. Some of these genes may have been acquired via horizontal gene transfer by a common ancestor of brown algae and dictyochophytes, together with genes involved in mannitol metabolism, which are also present in P. farcimen. Our findings may explain the unusual fatty acid profile previously observed in P. farcimen, and are discussed from an evolutionary perspective and in relation to the ichthyotoxicity of this alga

Genetic variation between Phytophthora cactorum isolates differing in their ability to cause crown rot in strawberry

Analysis of 44 isolates of Phytophthora cactorum, isolated from strawberry and other hosts, by AFLP showed that the crown rot pathotype is different from leather rot isolates and from P. cactorum isolated from other hosts. 16 of 23 crown rot isolates, including isolates from Europe, Japan, Australia, and New Zealand, were identical in an analysis based on 96 polymorphic bands from seven primer combinations. Leather rot isolates of strawberry could not be distinguished from isolates from other hosts. The pathogenicity test of all 44 isolates on strawberry plants mostly gave unambiguous results, except for three American isolates, which seemed to have reduced aggressiveness compared to the crown rot isolates. These isolates also differed in the AFLP analysis. Comparing information on the origin of the isolates with results from the pathogenicity test, showed that isolates from strawberry fruits or petioles could be either leather rot or crown rot pathotypes. None of the isolates from hosts other than strawberry caused crown rot symptoms in strawberr

Analysis of expressed sequence tags from the ichtyotoxic dictyochophyte Pseudochattonella farcimen

Pseudochattonella farcimen (Eikrem, Edvardsen, et Throndsen) is an ichthyotoxic alga within the Dictyochophyceae (Heterokonta), which has been shown to form blooms in Scandinavian waters every year since 1998. To improve our understanding of the biology of this alga and to facilitate future genomic studies, we report the sequencing and analysis of >10,000 expressed sequence tags (ESTs) corresponding to 8149 gene models from this species. A direct comparison with EST libraries from other heterokonts revealed several functional categories to be significantly overrepresented among the P. facimen ESTs, such as genes involved in cell communication, transporters, or genes targeted to cell organelles. Interestingly, P. farcimen ESTs also code for a high proportion (1.4%) of proteins related to fatty acid metabolism, including eight fatty acid desaturases and two phospholipase A2 genes. Three of the desaturases belong to a family of delta-4 desaturases, known so far only from haptophytes, where they catalyze the conversion of n3-docosapentaenoic (n3-DPA) acid to docosahexaenoic acid (DHA). These findings may partially explain the unusual fatty acid profiles observed in P. farcimen and are discussed both from an evolutionary point of view and in relation the ichthyotoxic effects of this alg

Gene gain and loss during evolution of obligate parasitism in the white rust pathogen of Arabidopsis thaliana

Biotrophic eukaryotic plant pathogens require a living host for their growth and form an intimate haustorial interface with parasitized cells. Evolution to biotrophy occurred independently in fungal rusts and powdery mildews, and in oomycete white rusts and downy mildews. Biotroph evolution and molecular mechanisms of biotrophy are poorly understood. It has been proposed, but not shown, that obligate biotrophy results from (i) reduced selection for maintenance of biosynthetic pathways and (ii) gain of mechanisms to evade host recognition or suppress host defence. Here we use Illumina sequencing to define the genome, transcriptome, and gene models for the obligate biotroph oomycete and Arabidopsis parasite, Albugo laibachii. A. laibachii is a member of the Chromalveolata, which incorporates Heterokonts (containing the oomycetes), Apicomplexa (which includes human parasites like Plasmodium falciparum and Toxoplasma gondii), and four other taxa. From comparisons with other oomycete plant pathogens and other chromalveolates, we reveal independent loss of molybdenum-cofactor-requiring enzymes in downy mildews, white rusts, and the malaria parasite P. falciparum. Biotrophy also requires ‘‘effectors’’ to suppress host defence; we reveal RXLR and Crinkler effectors shared with other oomycetes, and also discover and verify a novel class of effectors, the ‘‘CHXCs’’, by showing effector delivery and effector functionality. Our findings suggest that evolution to progressively more intimate association between host and parasite results in reduced selection for retention of certain biosynthetic pathways, and particularly reduced selection for retention of molybdopterinrequiring biosynthetic pathways. These mechanisms are not only relevant to plant pathogenic oomycetes but also to human pathogens within the Chromalveolata

Diversity patterns and activity of uncultured marine heterotrophic flagellates unveiled with pyrosequencing

11 pages, 7 figures, 2 tablesFlagellated heterotrophic microeukaryotes have key roles for the functioning of marine ecosystems as they channel large amounts of organic carbon to the upper trophic levels and control the population sizes of bacteria and archaea. Still, we know very little on the diversity patterns of most groups constituting this evolutionary heterogeneous assemblage. Here, we investigate 11 groups of uncultured flagellates known as MArine STramenopiles (MASTs). MASTs are ecologically very important and branch at the base of stramenopiles. We explored the diversity patterns of MASTs using pyrosequencing (18S rDNA) in coastal European waters. We found that MAST groups range from highly to lowly diversified. Pyrosequencing (hereafter ‘454’) allowed us to approach to the limits of taxonomic diversity for all MAST groups, which varied in one order of magnitude (tens to hundreds) in terms of operational taxonomic units (98% similarity). We did not evidence large differences in activity, as indicated by ratios of DNA:RNA-reads. Most groups were strictly planktonic, although we found some groups that were active in sediments and even in anoxic waters. The proportion of reads per size fraction indicated that most groups were composed of very small cells (~2–5 μm). In addition, phylogenetically different assemblages appeared to be present in different size fractions, depths and geographic zones. Thus, MAST diversity seems to be highly partitioned in spatial scales. Altogether, our results shed light on these ecologically very important but poorly known groups of uncultured marine flagellatesFinancial support for this work has been provided by a Marie Curie Intra-European Fellowship grant (PIEF-GA-2009-235365) to RL and by projects BioMarKs (2008-6530, ERA-net Biodiversa, EU) and FLAME (CGL2010-16304, MICINN, Spain) to RM. Large-scale computing resources were provided by the Canarian Institute of Astrophysics (www.iac.es), through the Barcelona Supercomputer Center and the Spanish Network of Supercomputing (grants BCV-2010-3-0003 and 2011-2-0003/3-0005 to RL and RM). We thank the BioMarKs consortium for undertaking the sampling and performing the initial laboratory processing of the samples, in particular Sarah Romac. We thank Hiroyuki Ogata and Jean-Michel Claverie for the implementation of bioinformatics tools through a BioMarKs grant and a project from the French National Research Agency (ANR-08-BDVA-003) to Jean-Michel Claverie. Javier del Campo is thanked for providing curated Sanger sequences of Ochrophyta. Berit Kaasa at the University of Oslo is thanked for running the nutrient analyses. We thank the three reviewers and the editor who helped to improve this workPeer reviewe

O ESPAÇO TERRITORIAL COMO REFERÊNCIA PARA A CONSTRUÇÃO DA CIDADANIA: UMA REFLEXÃO GEOGRÁFICA INTRODUTÓRIA SOBRE O PROBLEMA DAS DEMARCAÇÕES DE TERRAS DE POPULAÇÕES “REMANESCENTES”

Territorially, the Brazilian history is loaded with conflicts and antagonisms. The modernization towards the cities and expansion of the internal market of consumption, national foundations of the new order, conflicts, not a few times, with interests of local collectivities. The deliberate design of the state to achieve new levels of production, with the expansion of production and flow in the territory, has not been accompanied by a similar policy of effective recognition of the different "nations" that formed the national population. More recently, the surface is the discussion on the "remnants", new creations of social emerge where new political subjects. The recognition of these multiple subject presents a reality in which differ widely among themselves. Regarding the territorial quilombola, is the clear differentiation of strong socio-stamp this area both with regard to the origins and ownership of the land, about the events of this (cultural, religious, located in the national territory, the type of housing and size of the community, use of resources, training and recognition in the fight, and so on.). Before this destruction, the rearrangement of productive activities and cultural, produces new relationships that can be considered hybrid. This hybridization, however, follows the logic, it seems, apart from the inclusion.Territorialmente, a história brasileira é carregada de conflitos e antagonismos. A modernização rumo às cidades e a ampliação do mercado interno de consumo, alicerces da nova ordem nacional, conflita, não poucas vezes, com interesses de coletividades locais. O projeto deliberado do Estado de alcançar novos níveis produtivos, com a ampliação da produção e da fluidez dentro do território, não foi acompanhado de uma política semelhante de reconhecimento efetivo dos diferentes “povos” que compunham a população nacional. Mais recentemente, vem a tona a discussão sobre os “remanescentes”, novas criações sociais de onde emergem novos sujeitos políticos. O reconhecimento desses sujeitos apresenta uma realidade múltipla em que diferem bastante entre si. No que se refere à territorialidade quilombola, são nítidas as diferenciações de forte cunho sócio-territorial presente tanto no que diz respeito às origens e posse da terra, quanto às manifestações do presente (culturais, religiosas, de localização no território nacional, do tipo de habitação e tamanho da coletividade, uso dos recursos, estágio na luta e reconhecimento, etc.). Diante desta desestruturação, o rearranjo das atividades produtivas e culturais, produz novas relações que podem ser consideradas híbridas. Esta hibridização, no entanto, obedece a uma lógica, ao que parece, distante da inclusão