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Structural Flexibility Enables Alternative Maturation, ARGONAUTE Sorting and Activities of miR168, a Global Gene Silencing Regulator in Plants

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Molecular Plant 2018年第8期11卷 1008-1023页

作者： Taichiro Iki Antoine Cléry Nicolas G. Bologna Alexis Sarazin Christopher A. Brosnan Nathan Pumplin Frédéric H.T. Allain Olivier Voinnet Department of Biology Swiss Federal Institute of Technology (ETH) Universit&tstrasse 2 ZUrich 8092 Switzerland Institute of Molecular Biology and Biophysics Department of Biology Swiss Federal Institute of Technology (ETH) Zürich Switzerland Biomolecular NMR spectroscopy Platform ETH Zürich Switzerland Present address: Laboratory of Germline Biology Graduate School of Frontier Biosciences Osaka University 1-3 Yamadaoka Suita Osaka Japan

In eukaryotes, the RNase-Ⅲ Dicer often produces length/sequence microRNA （miRNA） variants, called ＂isomiRs＂, owing to intrinsic structural/sequence determinants of the miRNA precursors （pre-miRNAs）. In this study, we combined biophysics, genetics and biochemistry approaches to study Arabidopsis miR168, the key feedback regulator of central plant silencing effector protein ARGONAUTE1 （AGO1）. We identified a motif conserved among plant premiR168 orthologs, which enables flexible internal basepairing underlying at least three metastable structural configurations. These configurations promote alternative, accurate Dicer cleavage events generating length and structural isomiR168 variants with distinctive AGO sorting properties and modes of action. Among these isomiR168s, a duplex with a 22-nt guide strand exhibits strikingly preferential affinity for AGO10, the closest AGO1 paralog. The 22-nt miR168-AGO10 complex antagonizes AGO1 accumulation in part via ＂transitive RNAi＂, a silencing-amplification process, to maintain appropriate AGO1 cellular homeostasis. Furthermore, we found that the tombusviral P19 silencing-suppressor protein displays markedly weaker affinity for the 22-nt form among its isomiR168 cargoes, thereby promoting AGO10-directed suppression of AGOl-mediated antiviral silencing. Taken together, these findings indicate that structural flexibility, a previously overlooked property of premiRNAs, considerably increases the versatility and regulatory potential of individual MIRNA genes, and that some pathogens might have evolved the capacity or mechanisms to usurp this property.

关键词： microRNA miR168 Dicer ARGONAUTE tombusvirus P19

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Modeling the Ionosphere during Quiet Time Variation at Ouagadougou in West Africa

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International Journal of Astronomy and Astrophysics 2018年第2期8卷 163-170页

作者： Emmanuel Nanema Doua Allain Gnabahou Christian Zoundi Frédéric Ouattara Centre National de la Recherche Scientifique et Technologique (CNRST) Institut de Recherche en Sciences Appliquées et Technologies (IRSAT) Ouagadougou Burkina Faso Laboratoire de Recherche en Météorologie de l’Espace (LAREME) Université Norbert ZONGO Koudougou Burkina Faso

Ionosphere parameters determination is used to characterize its composition in particles. These results have been compared to data curried from Ouagadougou station. The present study deals with Total Electron Contents (TEC) results determined by Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) version 1.94 and International Reference Ionosphere (IRI) version 2012 during solar cycle 22. The minimum and maximum phases of solar cycle 22 are considered in this study for TEC determination. The station is located at Ouagadougou, in western Africa, characterized by its latitude (12.4°N) and longitude (358.5°E). The present study completes the two previous articles on hmF2 and foF2 parameters determination on the same station by comparison between TEC results carried out from TIEGCM and IRI models. So that, quiet time condition is determined by Aa (≤20 nt) for the five quietest days in each characteristic month of seasons. Rz values characterize minimum and maximum solar cycle phases.

关键词： Ionosphere TEC Solar Cycle Phases TIEGCM IRI

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What is a tree in the Mediterranean Basin hotspot?A critical analysis

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Forest Ecosystems 2019年第2期6卷 159-177页

作者： Frédéric Médail Anne-Christine Monnet Daniel Pavon Toni Nikolic Panayotis Dimopoulos Gianluigi Bacchetta Juan Arroyo Zoltán Barina Marwan Cheikh Albassatneh Gianniantonio Domina Bruno Fady Vlado Matevski Stephen Mifsud Agathe Leriche Aix Marseille Univ Avignon UnivCNRSIRDIMBE.Technopole de l’Arbois-Méditerranéecedex 4BP 8013 545 Aix-en-ProvenceFrance Macedonian Academy of Sciences and Arts Krste Misirkov 21000 SkopjeRepublic of Macedonia EcoGozo Regional Development Directorate-Ministry for GozoFlat 6Sunset Court BTriq MarsalfornXaghraGozoMalta Faculty of Science University of ZagrebHorvatovac 102aHR-10000 ZagrebCroatia Department of Biology Division of Plant BiologyLaboratory of BotanyUniversity of PatrasUniversity Campus26504 RioGreece Centro Conservazione Biodiversità Dipartimento di Scienze della Vita e dell’AmbienteUniversitàdegli Studi di CagliariViale S.Ignazio da Laconi1309123 CagliariItaly Departamento de Biologia Vegetal y Ecologia Universidad de SevillaApartado 109541080 SevillaSpain Department of Botany Hungarian Natural History MuseumPf.137Budapest 1431Hungary Sorbonne University IEES Bat 44-34cc 237.4Place JussieuParisFrance Department of Agriculture Food and Forest SciencesUniversity of PalermoViale delle Scienze bldg.490128 PalermoItaly INRA UR629Ecologie des forêts méditerranéennesAvignonFrance

Background: Tree species represent 20% of the vascular plant species worldwide and they play a crucial role in the global functioning of the biosphere. The Mediterranean Basin is one of the 36 world biodiversity hotspots, and it is estimated that forests covered 82% of the landscape before the first human impacts, thousands of years ago. However, the spatial distribution of the Mediterranean biodiversity is still imperfectly known, and a focus on tree species constitutes a key issue for understanding forest functioning and develop conservation strategies. Methods: We provide the first comprehensive checklist of all native tree taxa (species and subspecies) present in the Mediterranean-European region (from Portugal to Cyprus). We identified some cases of woody species difficult to categorize as trees that we further called "cryptic trees". We collected the occurrences of tree taxa by"administrative regions", i.e. country or large island, and by biogeographical provinces. We studied the species-area relationship, and evaluated the conservation issues for threatened taxa following IUCN criteria. Results: We identified 245 tree taxa that included 210 species and 35 subspecies, belonging to 33 families and 64 genera. It included 46 endemic tree taxa (30 species and 16 subspecies), mainly distributed within a single biogeographical unit. The countries with the highest tree richness are Greece (146 taxa), Italy (133), Albania (122), Spain (155), Macedonia (116), and Croatia (110). The species-area relationship clearly discriminated the richest central-eastern (Balkans) and northern (Alpine and Cevenno-Pyrenean) biogeographical provinces, against the five western provinces in the Iberian Peninsula. We identified 44 unrecognized "cryptic trees", representing 21% of the total trees. Among the 245 taxa identified, 19 are considered to be threatened (15 CR+EN+VU) or near threatened (4 nt) by IUCN. Conclusions: The Mediterranean-European region includes an unsuspectedly high nu

关键词： Plant biogeography Mediterranean region Threatened trees Tree definition Tree distributions

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