Small RNA Diversity in Plants and its Impact in Development

MicroRNAs are a class of non-coding RNAs involved in post-transcriptional control of gene expression, either via degradation or translational inhibition of target mRNAs. Both experimental and computational approaches have been used to identify miRNAs and their target genes. In plants, deep sequencing methods have recently allowed the analysis of small RNA diversity in different species and/or mutants. Most sequencing efforts have been concentrated on the identification of miRNAs and their mRNA targets have been predicted based on complementarity criteria. The recent demonstration that certain plant miRNAs could act partly via inhibition of protein translation certainly opens new fields of analysis for plant miRNA function on a broader group of targets. The roles of conserved miRNAs on target mRNA stability have been analysed in different species and defined common mechanisms in development and stress responses. In contrast, much less is known about expression patterns or functions of non-conserved miRNAs. In this review, we focus on the comparative analyses of plant small RNA diversity and the action of si/miRNAs in post-transcriptional regulation of some key genes involved in root development

A non-DNA-binding activity for the ATHB4 transcription factor in the control of vegetation proximity

Altres ajuts: Generalitat de Catalunya through the CERCA ProgramIn plants, perception of vegetation proximity by phytochrome photoreceptors activates a transcriptional network that implements a set of responses to adapt to plant competition, including elongation of stems or hypocotyls. In Arabidopsis thaliana, the homeodomain-leucine zipper (HD-Zip) transcription factor ARABIDOPSIS THALIANA HOMEOBOX 4 (ATHB4) regulates this and other responses, such as leaf polarity. To better understand the shade regulatory transcriptional network, we have carried out structure-function analyses of ATHB4 by overexpressing a series of truncated and mutated forms and analyzing three different responses: hypocotyl response to shade, transcriptional activity and leaf polarity. Our results indicated that ATHB4 has two physically separated molecular activities: that performed by HD-Zip, which is involved in binding to DNA-regulatory elements, and that performed by the ETHYLENE-RESPONSIVE ELEMENT BINDING FACTOR-associated amphiphilic repression (EAR)-containing N-terminal region, which is involved in protein-protein interaction. Whereas both activities are required to regulate leaf polarity, DNA-binding activity is not required for the regulation of the seedling responses to plant proximity, which indicates that ATHB4 works as a transcriptional cofactor in the regulation of this response. These findings suggest that transcription factors might employ alternative mechanisms of action to regulate different developmental processes

Approches génétiques et physiologiques de la rhizogenèse adventive chez Arabidopsis (vers une meilleure compréhension des mécanismes régulateurs)

LA RHIZOGENESE ADVENTIVE EST UN MECANISME ESSENTIEL POUR LA PROPAGATION D'ESPECES LIGNEUSES MAIS EGALEMENT POUR L'ADAPTATION A DES CONDITIONS ENVIRONNEMENTALES PARTICULIERES. C'EST UN PROCESSUS COMPLEXE AFFECTE PAR DE MULTIPLES FACTEURS TELS QUE L'AUXINE ET LA LUMIERE. IL EST AUSSI CONTROLE GENETIQUEMENT. CEPENDANT, LES MECANISMES MOLECULAIRES IMPLIQUES DANS CET ASPECT DU DEVELOPPEMENT SONT TRES MAL CONNUS. DISPOSANT DE PLUSIEURS MUTANTS D'A. THALIANA AFFECTES DANS LEUR CAPACITE A FAIRE DE LA RHIZOGENESE ADVENTIVE, NOUS AVONS PAR DES APPROCHES GENETIQUES ET PHYSIOLOGIQUES VOULU MIEUX COMPRENDRE QU'ELLES ETAIENT LES VOIES DE SIGNALISATION IMPLIQUEES. AINSI LA CARACTERISATION DES MUTANTS SUPERROOT (SUR1 ET SUR2) QUI FONT SPONTANEMENT DES RACINES ADVENTIVES ET ARGONAUTE1 (AGO1) QUI EN FONT DIFFICILEMENT, NOUS A PERMIS DE METTRE EN EVIDENCE L'INTERACTION ENTRE L'AUXINE ET LA LUMIERE. NOUS AVONS MONTRE QU'UNE MUTATION DANS LE GENE AGO1 PERTURBE L'HOMEOSTASIE DE L'AUXINE ET LES VOIES DE SIGNALISATION PAR LA LUMIERE. EN EFFET, LE MUTANT AGO1 EST HYPERSENSIBLE A LA LUMIERE ET A UN NIVEAU D'AUXINE LIBRE PLUS FAIBLE DANS LA PARTIE AERIENNE. CECI EST DE PLUS CORRELE AU DEFAUT DE RHIZOGENESE ADVENTIVE. DES APPROCHES DE PROTEOMIQUE ET DES ETUDES D'EXPRESSION DE CERTAINS GENES ONT PERMIS DE PROPOSER DES GENES CANDIDATS POTENTIELLEMENT IMPLIQUES DANS LE PROCESSUS DE RHIZOGENESE ADVENTIVE OU DANS LE CONTROLE DE L'HOMEOSTASIE DE L'AUXINE.ADVENTITIOUS ROOTING IS ESSENTIAL FOR PROPAGATION OF WOODY SPECIES AND FOR ADAPTATION TO PARTICULAR ENVIRONMENTAL CONDITIONS. IT IS A COMPLEX PROCESS AFFECTED BY MULTIPLE FACTORS LIKE AUXIN AND LIGHT. IT IS ALSO GENETICALLY CONTROLLED BUT THE MOLECULAR MECHANISMS INVOLVED ARE UNKNOWN. TO OBTAIN INSIGHT INTO THOSE MECHANISMS, A. THALIANA MUTANTS WERE UTILISED FOR A SERIES OF GENETIC AND PHYSIOLOGICAL EXPERIMENTS. THE IMPORTANCE OF AUXIN AND LIGHT IN THE REGULATION OF ADVENTITIOUS ROOTING WAS DEMONSTRATED BY THE CHARACTERISATION OF SUPERROOT (SUR1 AND SUR2) MUTANTS THAT SPONTANEOUSLY MAKE ADVENTITIOUS ROOTS, AND ARGONAUTE 1 (AGO1) MUTANTS THAT ARE BARELY ABLE TO MAKE ADVENTITIOUS ROOTS. WE HAVE SHOWN THAT A MUTATION IN AGO1 DISRUPT AUXIN HOMEOSTASIS AND LIGHT TRANSDUCTION PATHWAYS IN THE APICAL PART. THIS IS CORRELATED TO ADVENTITIOUS ROOTING DEFECT. PROTEOMICS AND GENE EXPRESSION ANALYSIS AT THE TRANSCRIPTIONAL LEVEL ALLOWED US TO PROPOSE CANDIDATES GENES POTENTIALLY INVOLVED IN ADVENTITIOUS ROOTING OR IN THE CONTROL OF AUXIN HOMEOSTASIS.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Les ARN non-codants impliqués dans la réponse des plantes aux contraintes environnementales

Les ARN ne codant pas de protéines (ou ARNnc) ont émergé ces dernières années comme une part essentielle du transcriptome des cellules eucaryotes. Les approches récentes de génomique ont en effet permis de découvrir une grande variété d’ARNnc, de petite ou de grande taille, impliqués dans des réseaux de régulations moléculaires très complexes. Bien que de nombreux longs ARNnc soient régulés en réponse aux stresses abiotiques, leur fonction demeure mal comprise. Les petits ARN, quant à eux, sont des acteurs majeurs de la régulation génique aussi bien au niveau transcriptionnel que post-transcriptionnel. Ainsi, plusieurs d’entre eux jouent des rôles essentiels dans la réponse des plantes aux stresses. Dans cette revue, nous présenterons certains ARNnc associés aux contraintes environnementales (salinité, froid ou carence nutritionnelle) chez les végétaux. La compréhension des réseaux de régulations liés à ces ARN régulateurs devrait permettre de mettre en évidence de nouveaux mécanismes associés à l’adaptation des plantes à leur environnement

Arabidopsis CLAVATA1 and CLAVATA2 receptors contribute to Ralstonia solanacearum pathogenicity through a miR169-dependent pathway

Bacterial wilt caused by Ralstonia solanacearum is one of the most destructive bacterial plant diseases. Although many molecular determinants involved in R. solanacearum adaptation to hosts and pathogenesis have been described, host components required for disease establishment remain poorly characterized. Phenotypical analysis of Arabidopsis mutants for leucine-rich repeat (LRR)-receptor-like proteins revealed that mutations in the CLAVATA1 (CLV1) and CLAVATA2 (CLV2) genes confer enhanced disease resistance to bacterial wilt. We further investigated the underlying mechanisms using genetic, transcriptomic and molecular approaches. The enhanced resistance of both clv1 and clv2 mutants to the bacteria did not require the well characterized CLV signalling modules involved in shoot meristem homeostasis, and was conditioned by neither salicylic acid nor ethylene defence-related hormones. Gene expression microarray analysis performed on clv1 and clv2 revealed deregulation of genes encoding nuclear transcription factor Y subunit alpha (NF-YA) transcription factors whose post-transcriptional regulation is known to involve microRNAs from the miR169 family. Both clv mutants showed a defect in miR169 accumulation. Conversely, overexpression of miR169 abrogated the resistance phenotype of clv mutants. We propose that CLV1 and CLV2, two receptors involved in CLV3 perception during plant development, contribute to bacterial wilt through a signalling pathway involving the miR169/NF-YA module

Systemic Propagation of a Fluorescent Infectious Clone of a Polerovirus Following Inoculation by Agrobacteria and Aphids

BGPI : équipe 2International audienceA fluorescent viral clone of the polerovirus Turnip yellows virus (TuYV) was engineered by introducing the Enhanced Green Fluorescent Protein (EGFP) sequence into the non-structural domain sequence of the readthrough protein, a minor capsid protein. The resulting recombinant virus, referred to as TuYV-RTGFP, was infectious in several plant species when delivered by agroinoculation and invaded efficiently non-inoculated leaves. As expected for poleroviruses, which infect only phloem cells, the fluorescence emitted by TuYV-RTGFP was restricted to the vasculature of infected plants. In addition, TuYV-RTGFP was aphid transmissible and enabled the observation of the initial sites of infection in the phloem after aphid probing in epidermal cells. The aphid-transmitted virus moved efficiently to leaves distant from the inoculation sites and importantly retained the EGFP sequence in the viral genome. This work reports on the first engineered member in the Luteoviridae family that can be visualized by fluorescence emission in systemic leaves of different plant species after agroinoculation or aphid transmissio

A fluorescent infectious clone of Turnip yellows virus to study the effect of aphid infestation on virus distribution in planta

BGPI : équipe 2Turnip yellows virus (TuYV) is a polerovirus (family Luteoviridae) restricted to phloem tissue and obligatorily transmitted by aphids in a circulative and non-propagative mode. This virus infects several plant species of economic importance. The icosahedral viral particles contain a single positive strand RNA genome. In order to track virus movement in plants and to measure the impact of aphids presence on virus distribution in plants, a GFP-tagged virus was engineered (TuYV-GFP). In this construct, the GFP sequence was inserted in a non-structural protein sequence involved, to some extent, in virus movement. The fluorescent signal is expected to label virus replicating cells. The TuYV-GFP sequence was introduced into a binary vector to inoculate several plant species by agro infiltration. TuYV-GFP was able to replicate and to move in A. thaliana, N.benthamiana and M. perfoliata. Accumulation of TuYV-GFP was however reduced when compared to the wild type virus. The impaired ability of the recombinant virus to reach efficiently non inoculated leaves is likely due to the insertion of the GFP sequence in the viral genome. The TuYVGFP genome was stable in N. benthamiana while it was subjected to partial deletions in A. thalianaand in M. perfoliata. Nevertheless, we observed fluorescent phloem cells in non-inoculated leaves of the three plant species. Importantly, fluorescent phloem cells were also observed after virus acquisition and inoculation by aphids, both in inoculated and non-inoculated leaves. This major breakthrough in the study of poleroviruses persistently transmitted by aphids will now be used to address whether the virus localisation in planta is affected following aphid infestation

ATHB4, a regulator of shade avoidance, modulates hormone response in Arabidopsis seedlings

Plants sense the presence of competing neighboring vegetation as a change in light quality: i.e. they sense the reduced ratio of red light to far-red light. The responses to shade are generally referred to as the shade avoidance syndrome (SAS), and involve various developmental changes intended to outgrow or outcompete the neighboring plants. Here, we analyze the function of ATHB4, a gene encoding a homeodomain-leucine zipper (HD-Zip) class-II transcription factor from Arabidopsis thaliana, the expression of which is rapidly and directly upregulated after proximity perception by the phytochrome photoreceptors. ATHB4 acts redundantly with other members of the HD-Zip class-II transcription factors. The expression of these genes is regulated by other members of the same class, forming a small transcriptional network of factors in which homeostasis is mutually controlled. Our results suggest that some members of this small gene subfamily can modulate SAS responses by controlling auxin, brassinosteroid and gibberellin molecular and/or physiological responsiveness. In particular, we propose ATHB4 as a new shade signaling component that participates in integrating shade perception and hormone-mediated growth.CS and JB-T’s financial support came from the Generalitat de Catalunya (GC) (C-RED Program). JB-T also acknowledges financial support from the CRAG. MS-M and IR-V received pre-doctoral fellowships from the CSIC and the Spanish Ministry of Science and Education (MEC), respectively. Our research is supported by grants from the GC (Xarxa de Referència en Biotecnologia) and MEC–FEDER to JFM-G (BIO2005-00154 and BIO2008-00169).Peer reviewe