Reduction in PLANT DEFENSIN 1 expression in Arabidopsis thaliana results in increased resistance to pathogens and zinc toxicity.

Ectopic expression of defensins in plants correlates with their increased capacity to withstand abiotic and biotic stresses. This applies to Arabidopsis thaliana, where some of the seven members of the PLANT DEFENSIN 1 family (AtPDF1) are recognised to improve plant responses to necrotrophic pathogens and increase seedling tolerance to excess zinc (Zn). However, few studies have explored the effects of decreased endogenous defensin expression on these stress responses. Here, we carried out an extensive physiological and biochemical comparative characterization of (i) novel artificial microRNA (amiRNA) lines silenced for the five most similar AtPDF1s, and (ii) a double null mutant for the two most distant AtPDF1s. Silencing of five AtPDF1 genes was specifically associated with increased aboveground dry mass production in mature plants under excess Zn conditions, and with increased plant tolerance to different pathogens - a fungus, an oomycete and a bacterium, while the double mutant behaved similarly to the wild type. These unexpected results challenge the current paradigm describing the role of PDFs in plant stress responses. Additional roles of endogenous plant defensins are discussed, opening new perspectives for their functions.

Functional characterization of the chaperon-like protein Cdc48 in cryptogein-induced immune response in tobacco.

Cdc48, a molecular chaperone conserved in different kingdoms, is a member of the AAA+ family contributing to numerous processes in mammals including proteins quality control and degradation, vesicular trafficking, autophagy and immunity. The functions of Cdc48 plant orthologues are less understood. We previously reported that Cdc48 is regulated by S-nitrosylation in tobacco cells undergoing an immune response triggered by cryptogein, an elicitin produced by the oomycete Phytophthora cryptogea. Here, we inv estigated the function of NtCdc48 in cryptogein signalling and induced hypersensitive-like cell death. NtCdc48 was found to accumulate in elicited cells at both the protein and transcript levels. Interestingly, only a small proportion of the overall NtCdc48 population appeared to be S-nitrosylated. Using gel filtration in native conditions, we confirmed that NtCdc48 was present in its hexameric active form. An immunoprecipitation-based strategy following my mass spectrometry analysis led to the identification of about a hundred NtCdc48 partners and underlined its contribution in cellular processes including targeting of ubiquitylated proteins for proteasome-dependent degradation, subcellular trafficking and redox regulation. Finally, the analysis of cryptogein-induced events in NtCdc48-overexpressing cells highlighted a correlation between NtCdc48 expression and hypersensitive cell death. Altogether, this study identified NtCdc48 as a component of cryptogein signalling and plant immunity.

The endophytic strain Fusarium oxysporum Fo47: a good candidate for priming the defense responses in tomato roots.

The protective Fusarium oxysporum strain Fo47 is effective in controlling Fusarium wilt in tomato. Previous studies have demonstrated the role of direct antagonism and involvement of induced resistance. The aim of the present study was to investigate whether priming of plant defense responses is a mechanism by which Fo47 controls Fusarium wilt. An in vitro design enabled inoculation of the tap root with Fo47 and the pathogenic strain (Fol8) at different locations and different times. The expression levels of six genes known to be involved in tomato defense responses were quantified using reverse-transcription quantitative polymerase chain reaction (qPCR). Three genes-CHI3, GLUA, and PR-1a-were overexpressed in the root preinoculated with Fo47, and then challenged with Fol8. The genes GLUA and PR-1a were upregulated in cotyledons after inoculation of Fo47. Fungal growth in the root was assessed by qPCR, using specific markers for Fo47 and Fol8. Results showed a reduction of the pathogen growth in the root of the tomato plant preinoculated with Fo47. This study demonstrated that priming of tomato defense responses is one of the mechanisms of action of Fo47, which induces a reduced colonization of the root by the pathogen.

1H, 13C and 15N chemical shift backbone resonance NMR assignment of tobacco calmodulin 2.

Calcium is a ubiquitous second messenger regulating numbers of cellular processes in living organisms. It encodes and transmits information perceived by cells to downstream sensors, including calmodulin (CaM), that initiate cellular responses. In plants, CaM has been involved in the regulation of plant responses to biotic and abiotic environmental cues. Plant CaMs possess a cysteine residue in their first calcium-binding motif EF-hand, which is not conserved in other eucaryotic organisms. In this work, we report the near-complete backbone chemical shift assignment of tobacco CaM2 with calcium. These results will be useful to study the impact of this particular EF-hand domain regarding CaM interaction with partners involved in stress responses.

Some Plant Defense Stimulators can induce IL-1ß production in human immune cells in vitro.

Among Plant Protection Products (PPP), a new emerging category of pesticides act by stimulating plant defense in order to improve plant resistance against microbial pathogens. Given that these compounds, the so-called Plant Defense Stimulators (PDS) act on innate immunity, we tested, using an in vitro approach on human mononuclear leucocytes (PBMC), the potential toxicity (XTT assay) and inflammatory effects (production of IL-1ß) of 4 PPP belonging to different chemical families. We found that two products (LBG-01F34® and Regalis®) did not induce any cytotoxicity or IL-1 ß production. The product BION-50 WG®, that contains Acibenzolar-S-methyl (ASM) and silica particles did not present any cytotoxicity but induced a significant increase in the production of the inflammatory cytokine IL-1 ß. Finally, Vacciplant® that contains laminarin, was highly cytotoxic and pro-inflammatory. It induced a strong production of IL-1 ß when used at a concentration in the culture medium, as low as 0.02 mg/mL. We also tested the potential toxic effect of these 4 PPP on 4 days old zebra fish larvae. After 24 h of exposure, our results indicate that Vacciplant® induced zebra fish larvae mortality at concentration of 20 µg/mL. LBG did not induced significant mortality at concentrations up to 1 mg/mL whereas Regalis was lethal for 0,3 mg/mL concentrations and BION-50 WG began to induce mortality at 2,5 mg/mL. Our results indicate possible effects of PDS on IL-1ß production in human cells and fish survival, calling for more studies on the potential noxious side effects of these compounds.

Analysis of Recombinant Protein S-Nitrosylation Using the Biotin-Switch Technique.

Nitric oxide is regarded as a key signaling messenger in several organisms. Its physiological relevance is partly due to its capacity to induce posttranslational modifications of proteins through its direct or indirect reaction with specific amino acid residues. Among them, S-nitrosylation has been shown to be involved in a broad range of cellular signaling pathways both in animals and plants. The identification of S-nitrosylated proteins has been made possible by the development of the Biotin-Switch Technique (BST) in the early 2000s. Here, we describe the BST protocol we routinely use to check in vitro S-nitrosylation of recombinant proteins induced by NO donors.

Evolutionary diversification of type-2 HDAC structure, function and regulation in Nicotiana tabacum.

Type-2 HDACs (HD2s) are plant-specific histone deacetylases that play diverse roles during development and in responses to biotic and abiotic stresses. In this study we characterized the six tobacco genes encoding HD2s that mainly differ by the presence or the absence of a typical zinc finger in their C-terminal part. Of particular interest, these HD2 genes exhibit a highly conserved intron/exon structure. We then further investigated the phylogenetic relationships among the HD2 gene family, and proposed a model of the genetic events that led to the organization of the HD2 family in Solanaceae. Absolute quantification of HD2 mRNAs in N. tabacum and in its precursors, N. tomentosiformis and N. sylvestris, did not reveal any pseudogenization of any of the HD2 genes, but rather specific regulation of HD2 expression in these three species. Functional complementation approaches in Arabidopsis thaliana demonstrated that the four zinc finger-containing HD2 proteins exhibit the same biological function in response to salt stress, whereas the two HD2 proteins without zinc finger have different biological function.

Protein S-nitrosylation: specificity and identification strategies in plants.

The role of nitric oxide (NO) as a major regulator of plant physiological functions has become increasingly evident. To further improve our understanding of its role, within the last few years plant biologists have begun to embrace the exciting opportunity of investigating protein S-nitrosylation, a major reversible NO-dependent post-translational modification (PTM) targeting specific Cys residues and widely studied in animals. Thanks to the development of dedicated proteomic approaches, in particular the use of the biotin switch technique (BST) combined with mass spectrometry, hundreds of plant protein candidates for S-nitrosylation have been identified. Functional studies focused on specific proteins provided preliminary comprehensive views of how this PTM impacts the structure and function of proteins and, more generally, of how NO might regulate biological plant processes. The aim of this review is to detail the basic principle of protein S-nitrosylation, to provide information on the biochemical and structural features of the S-nitrosylation sites and to describe the proteomic strategies adopted to investigate this PTM in plants. Limits of the current approaches and tomorrow's challenges are also discussed.

Development of a strain-specific real-time PCR assay for the detection and quantification of the biological control agent Fo47 in root tissues.

Being able to identify specifically a biological control agent at the strain level is not the only requirement set by regulations (EC)1107/2009, it is also necessary to study the interactions of the agent with the plant and the pathogen in the rhizosphere. Fo47 is a soil-borne strain of Fusarium oxysporum which has the capacity to protect several plant species against the pathogenic formae speciales of F. oxysporum inducing wilts. A strain-specific sequence-characterized amplified region marker has been designed which makes it possible to distinguish Fo47 from other strains of F. oxysporum. In addition, a real-time PCR assay has been developed to quantify Fo47 in root tissues. The proposed assay has been validated by following the dynamics of root colonization of tomato plants grown in soil infested with Fo47. Results showed that with the method it is possible to quantify Fo47 in roots in the absence or presence of the pathogen and in the absence or in presence of the native microbial communities.

Ecological fitness of the biocontrol agent Fusarium oxysporum Fo47 in soil and its impact on the soil microbial communities.

Some nonpathogenic strains of Fusarium oxysporum can control Fusarium diseases responsible for severe damages in many crops. Success of biological control provided by protective strains requires their establishment in the soil. The strain Fo47 has proved its efficacy under experimental conditions, but its ecological fitness has not been carefully studied. In a series of microcosm studies, the ability of a benomyl-resistant mutant Fo47b10 to establish in two different soils was demonstrated. One year after its introduction at two concentrations in the disinfected soils, the biocontrol agent (BCA) established at similar high population densities, whereas in the nondisinfected soils it survived at lower densities, related to the initial concentrations at which it was introduced. The BCA behaved similarly in the two soils at temperatures ranging from 5 to 25 degrees C and soil water potentials between -0.01 and -1.5 MPa. In addition, terminal restriction fragment length polymorphism analysis of 16S and 18S rRNA showed that the structures of the bacterial and fungal communities evolved with time but were not significantly affected by the introduction of the BCA. Overall, the results showed that Fo47 is potentially a good BCA, able to establish in different soil environments without perturbing the investigated microbial structures.