Increased sensitivity to iron deficiency in Arabidopsis thaliana overaccumulating nicotianamine

Nicotianamine (NA) is a non-protein amino acid derivative synthesized from S-adenosyl L-methionine able to bind several metal ions such as iron, copper, manganese, zinc, or nickel. In plants, NA appears to be involved in iron availability and is essential for the plant to complete its biological cycle. In graminaceous plants, NA is also the precursor in the biosynthesis of phytosiderophores. Arabidopsis lines accumulating 4- and 100-fold more NA than wild-type plants were used in order to evaluate the impact of such an NA overaccumulation on iron homeostasis. The expression of iron-regulated genes including the IRT1/FRO2 iron uptake system is highly induced at the transcript level under both iron-sufficient and iron-deficient conditions. Nevertheless, NA overaccumulation does not interfere with the iron uptake mechanisms since the iron levels are similar in the NA-overaccumulating line and wild-type plants in both roots and leaves under both sufficient and deficient conditions. This observation also suggests that the translocation of iron from the root to the shoot is not affected in the NA-overaccumulating line. However, NA overaccumulation triggers an enhanced sensitivity to iron starvation, associated with a decrease in iron availability. This study draws attention to a particular phenotype where NA in excess paradoxically leads to iron deficiency, probably because of an increase of the NA apoplastic pool sequestering iron. This finding strengthens the notion that extracellular NA in the apoplast could be a major checkpoint to control plant iron homeostasis

Etude du rôle de la nicotianamine dans l'homéostasie du fer et caractérisation fonctionnelle de ses transporteurs potentiels chez Arabidopsis thaliana

Etant donné les propriétés physico-chimiques du fer, sa circulation dans les végétaux est contrôlée à tous les niveaux. Dans ce schéma général, le contrôle du transport longue distance, ainsi que la distribution intracellulaire restent à ce jour les étapes les moins documentées. Au niveau cellulaire, ce travail rapporte l'étude d'une suraccumulation de nicotianamine (NA, un chélat du fer) sur la réponse dArabidopsis à la carence ou l'excès de fer. La caractérisation de lignées suraccumulant 100 ou 4 fois plus de NA foliaire montre qu'elles sont plus sensibles à une carence ou à un excès de fer probablement du fait d'une mauvaise localisation du fer. En condition de suffisance ou de carence en fer, la suraccumulation de NA s'accompagne d'une augmentation de la concentration en fer apoplasmique dans les feuilles. Ce résultat suggère un rôle de la NA dans la compartimentation du fer dans l'apoplasme. Par ailleurs, en réponse à l'excès de fer, une diminution de la concentration en NA est observée dans les chloroplastes des plantes sauvages sans modification de la teneur en fer, tandis que dans la lignée suraccumulant la NA, les chloroplastes contiennent 250 fois plus de NA que les plantes sauvages et voient leur teneur en fer augmenter. Ces résultats mettent en évidence pour la première fois un adressage de la NA aux chloroplastes et suggèrent un rôle de la NA dans la teneur en fer chloroplastique. L'identification de la famille de transporteurs YSL, dont certains membres chez diverses espèces de plantes ont une activité de transport de complexes NA-métaux, ouvre la voie à l'étude du transport longue distance du fer. Une étude du rôle des transporteurs de la sous-famille AtYSL5, 7, 8 d'Arabidopsis thaliana dans l'homéostasie métallique en général et du fer en particulier, a été menée. Les simples mutants ysl5-1, ysl7-1 et ysl8-1, ainsi que les doubles mutants ysl5ysl8 et ysl7ysl8 ne présentent pas de phénotype. En revanche, ysl5ysl7 a un retard de montaison et produit un faible nombre de graines. Ce défaut est lié aux diminutions de la viabilité des grains de pollen et du nombre d'ovules produits par pistil dans les fleurs ysl5ysl7. De plus, les graines ysl5ysl7 accumulent une grande quantité de Fe, Zn, Mn et Cu. L'expression du gène AtYSL7 est restreinte aux grains de pollen alors que celle du gène AtYSL5 est présente dans tous les organes de la plante. Ces résultats sont compatibles avec un rôle d'AtYSL5 et AtYSL7 dans le transport de métaux dans la fleur et dans le maintien de l'homéostasie métallique de la graineDue to its physicochemical properties, iron circulation within plants has to be strictly controlled. In this general scheme, our knowledge concerning long distance transport and intracellular distribution remains the least documented. At the cellular level, this work reports on the study of nicotianamine (NA, an iron chelator) over-accumulation on the response of Arabidopsis to iron starvation or excess. Two lines over-accumulating 4- and 100-fold more NA were characterized and shown to be more sensitive to both iron conditions probably due to iron misallocation. Under iron sufficient condition, NA over-accumulation is associated with an increase of the iron apoplastic pool in the leaves. This result suggests a role for NA in the localization of iron within the apoplast. Upon iron excess, a decrease of the chloroplast NA content with no change in the iron level was observed in wild-type plants whereas in the NA over-accumulating line that contains 250 fold more NA in the chloroplast, an iron increase was measured in the chloroplast. These results identifies for the first time a targeting of the NA to the chloroplast, and support a role for NA in chloroplast iron content. Members of the YSL transporter family have been shown to possess NA-metals transport capability. The YSL represent therefore potential candidates for the long distance transport of iron. I have undergone the characterization of the AtYSL5, 7 and 8 sub-family in Arabidopsis with respect to metals and iron homeostasis. The single ysl5-1, ysl7-1 and ysl8-1 as well as the double ysl5ysl8 and ysl7ysl8 mutants have no macroscopic phenotypes. However, the ysl5ysl7 double mutant present late bolting and sets very few seeds. This latter phenotype has been attributed to reduced pollen viability and ovules production of the ysl5ysl7 flower. In addition, ysl5ysl7 seeds contain increased concentration of Fe, Zn, Mn and Cu. AtYSL7 gene expression is restricted to pollen grains whereas AtYSL5 is ubiquitously expressed within the plant. These results are consistent with a role of the AtYSL 5 and 7 transporters in the delivery of metals to the flowers and in maintaining seed metal homeostasisMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Identification and characterization of cDNA clones encoding hydroxycinnamoyl-CoA:tyramine N-hydroxycinnamoyltransferase from tobacco

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Screening for a homologue of the yeast negative regulator of proline catabolism in Arabidopsis thaliana

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Symbiotic compatibility between rice cultivars and arbuscular mycorrhizal fungi genotypes affects rice growth and mycorrhiza-induced resistance

International audienceIntroduction: Arbuscular mycorrhizal fungi (AMF) belong to the Glomeromycota clade and can form root symbioses with 80% of Angiosperms, including crops species such as wheat, maize and rice. By increasing nutrient availability, uptake and soil anchoring of plants, AMF can improve plant’s growth and tolerance to abiotic stresses. AMF can also reduce symptoms and pathogen load on infected plants, both locally and systemically, through a phenomenon called mycorrhiza induced resistance (MIR). There is scarce information on rice mycorrhization, despite the high potential of this symbiosis in a context of sustainable water management in rice production systems.Methods: We studied the symbiotic compatibility (global mycorrhization & arbuscules intensity) and MIR phenotypes between six rice cultivars from two subspecies (indica: IR64 & Phka Rumduol; japonica: Nipponbare, Kitaake, Azucena & Zhonghua 11) and three AMF genotypes (Funneliformis mosseae FR140 (FM), Rhizophagus irregularis DAOM197198 (RIR) & R. intraradices FR121 (RIN)). The impact of mycorrhization on rice growth and defence response to Xanthomonas oryzae pv oryzae (Xoo) infection was recorded via both phenotypic indexes and rice marker gene expression studies.Results: All three AMF genotypes colonise the roots of all rice varieties, with clear differences in efficiency depending on the combination under study (from 27% to 84% for Phka Rumduol-RIN and Nipponbare-RIR combinations, respectively). Mycorrhization significantly (α=0.05) induced negative to beneficial effects on rice growth (impact on dry weight ranging from -21% to 227% on Azucena-FM and Kitaake-RIN combinations, respectively), and neutral to beneficial effects on the extent of Xoo symptoms on leaves (except for Azucena-RIN combination which showed a 68% increase of chlorosis). R. irregularis DAOM197198 was the most compatible AMF partner of rice, with high root colonisation intensity (84% of Nipponbare’s roots hyphal colonisation), beneficial effects on rice growth (dry weight +28% (IR64) to +178% (Kitaake)) and decrease of Xoo-induced symptoms (-6% (Nipponbare) to -27% (IR64)). Transcriptomic analyses by RT-qPCR on leaves of two rice cultivars contrasting in their association with AMF show two different patterns of response on several physiological marker genes

Characterization of an Arabidopsis thaliana receptor like protein kinase gene activated by salicylic acid and hypo-osmotic and oxidative stresses

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Synthesis and biological activity of nicotianamine and analogues

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Monitoring of Rice Transcriptional Responses to Contrasted Colonizing Patterns of Phytobeneficial Burkholderia s.l. Reveals a Temporal Shift in JA Systemic Response.

In the context of plant-pathogen and plant-mutualist interactions, the underlying molecular bases associated with host colonization have been extensively studied. However, it is not the case for non-mutualistic beneficial interactions or associative symbiosis with plants. Particularly, little is known about the transcriptional regulations associated with the immune tolerance of plants towards beneficial microbes. In this context, the study of the Burkholderia rice model is very promising to describe the molecular mechanisms involved in associative symbiosis. Indeed, several species of the Burkholderia sensu lato (s.l.) genus can colonize rice tissues and have beneficial effects; particularly, two species have been thoroughly studied: Burkholderia vietnamiensis and Paraburkholderia kururiensis. This study aims to compare the interaction of these species with rice and especially to identify common or specific plant responses. Therefore, we analyzed root colonization of the rice cultivar Nipponbare using DsRed-tagged bacterial strains and produced the transcriptomes of both roots and leaves 7 days after root inoculation. This led us to the identification of a co-expression jasmonic acid (JA)-related network exhibiting opposite regulation in response to the two strains in the leaves of inoculated plants. We then monitored by quantitative polymerase chain reaction (qPCR) the expression of JA-related genes during time course colonization by each strain. Our results reveal a temporal shift in this JA systemic response, which can be related to different colonization strategies of both strains

Preliminary insights into the diversity of the rice root microbiome in a field highly infested by Meloidogyne graminicola

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