Induced Systemic Resistance (ISR) in Arabidopsis thaliana by Bacillus amyloliquefaciens and Trichoderma harzianum Used as Seed Treatments

International audienceThe Trichoderma fungal species and the bacteria Bacillus species were described as inducers of plant systemic resistance in relation to their antagonistic activity. The objective of this study was to evaluate the effect of selected strains of Bacillus amyloliquefaciens (I3) and Trichoderma harzianum (A) on inducing systemic resistance in Arabidopsis thaliana as a model for plant molecular genetics. The microorganisms were identified and were confirmed for their antagonistic potential in vitro and in vivo in previous studies. In order to explore this mechanism, two mutants of A. thaliana carrying a PR1 promoter (a conventional marker of salicylic acid (SA) pathway) and LOX2 promoter (a marker triggering jasmonic acid (JA) pathway activation) were analyzed after inoculating antagonists. Transgenic reporter line analysis demonstrated that B. amyloliquefaciens I3 and T. harzianum A induce A. thaliana defense pathways by activating SA and JA at a high level compared to lines treated with chemical elicitors of references (acibenzolar-S-methyl (Bion 50 WG (water-dispersible granule)), SA, and methyl jasmonate). The efficacy of B. amyloliquefaciens I3 and T. harzianum A in inducing the defense mechanism in A. thaliana was demonstrated in this study

Arabidopsis transcriptome dataset of the response of imbibed wild-type and glucosinolate-deficient seeds to nitrogen-containing compounds

The presented RNAseq data were obtained from Arabidopsis seeds dry and 6h imbibed to describe, in wild-type and glucosinolate (GSL)-deficient genotypes, the response at the RNA level to nitrogen compounds, i.e., potassium nitrate (KNO3, 10mM), potassium thiocyanate (KSCN, 8µM). The cyp79B2 cyp79B3 (cyp79B2/B3) double mutant deficient in Indole GSL, the myb28 myb29 (myb28/29) double mutant deficient in aliphatic GSL, the quadruple mutant cyp79B2 cyp79B3 myb28 myb29 (qko) deficient in total GSL in the seed and the WT reference genotype in Col-0 background were used for the transcriptomic analysis. Total ARN was extracted using NucleoSpin® RNA Plant and Fungi kit. Library construction and sequencing were performed with DNBseq™ technology at Beijing Genomics Institute. FastQC was used to check reads quality and mapping analysis were made using a quasi-mapping alignment from Salmon. Gene expression changes in mutant seeds compared to WT were calculated using DESeq2 algorithms. This comparison with the qko, cyp79B2/B3 and myb28/29 mutants made it possible to identify 30220, 36885 and 23807 differentially expressed genes (DEGs), respectively. Mapping rate result was merge into a single report using MultiQC; graphic results were illustrated through Veen diagrams and volcano plots. Fastq raw data and count files from 45 samples are available in the repository Sequence Read Archive (SRA) of the National Center for Biotechnology Information (NCBI) and can be consulted with the data identification number GSE221567 at https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE221567

ScreenSeed as a novel high throughput seed germination phenotyping method

International audienceA high throughput phenotyping tool for seed germination, the ScreenSeed technology, was developed with the aim of screening genotype responsiveness and chemical drugs. This was presently used with Arabidopsis thaliana seeds to allow characterizing seed samples germination behavior by incubating seeds in 96-well microplates under defined conditions and detecting radicle protrusion through the seed coat by automated image analysis. This study shows that this technology provides a fast procedure allowing to handle thousands of seeds without compromising repeatability or accuracy of the germination measurements. Potential biases of the experimental protocol were assessed through statistical analyses of germination kinetics. Comparison of the ScreenSeed procedure with commonly used germination tests based upon visual scoring displayed very similar germination kinetics

Induced Systemic Resistance (ISR) in Arabidopsis thaliana by Bacillus amyloliquefaciens and Trichoderma harzianum Used as Seed Treatments

The Trichoderma fungal species and the bacteria Bacillus species were described as inducers of plant systemic resistance in relation to their antagonistic activity. The objective of this study was to evaluate the effect of selected strains of Bacillus amyloliquefaciens (I3) and Trichoderma harzianum (A) on inducing systemic resistance in Arabidopsis thaliana as a model for plant molecular genetics. The microorganisms were identified and were confirmed for their antagonistic potential in vitro and in vivo in previous studies. In order to explore this mechanism, two mutants of A. thaliana carrying a PR1 promoter (a conventional marker of salicylic acid (SA) pathway) and LOX2 promoter (a marker triggering jasmonic acid (JA) pathway activation) were analyzed after inoculating antagonists. Transgenic reporter line analysis demonstrated that B. amyloliquefaciens I3 and T. harzianum A induce A. thaliana defense pathways by activating SA and JA at a high level compared to lines treated with chemical elicitors of references (acibenzolar-S-methyl (Bion 50 WG (water-dispersible granule)), SA, and methyl jasmonate). The efficacy of B. amyloliquefaciens I3 and T. harzianum A in inducing the defense mechanism in A. thaliana was demonstrated in this study

Nitrogen Nutrition Modulates the Response to <i>Alternaria brassicicola</i> Infection via Metabolic Modifications in <i>Arabidopsis</i> Seedlings

Little is known about the effect of nitrogen nutrition on seedling susceptibility to seed-borne pathogens. We have previously shown that seedlings grown under high nitrate (5 mM) conditions are less susceptible than those grown under low nitrate (0.1 mM) and ammonium (5 mM) in the Arabidopsis-Alternaria brassicicola pathosystem. However, it is not known how seedling metabolism is modulated by nitrogen nutrition, nor what is its response to pathogen infection. Here, we addressed this question using the same pathosystem and nutritive conditions, examining germination kinetics, seedling development, but also shoot ion contents, metabolome, and selected gene expression. Nitrogen nutrition clearly altered the seedling metabolome. A similar metabolomic profile was observed in inoculated seedlings grown at high nitrate levels and in not inoculated-seedlings. High nitrate levels also led to specific gene expression patterns (e.g., polyamine metabolism), while other genes responded to inoculation regardless of nitrogen supply conditions. Furthermore, the metabolites best correlated with high disease symptoms were coumarate, tyrosine, hemicellulose sugars, and polyamines, and those associated with low symptoms were organic acids (tricarboxylic acid pathway, glycerate, shikimate), sugars derivatives and β-alanine. Overall, our results suggest that the beneficial effect of high nitrate nutrition on seedling susceptibility is likely due to nutritive and signaling mechanisms affecting developmental plant processes detrimental to the pathogen. In particular, it may be due to a constitutively high tryptophan metabolism, as well as down regulation of oxidative stress caused by polyamine catabolism

Role of Membrane Compartment Occupied by Can1 (MCC) and eisosome subdomains in plant pathogenicity of the necrotrophic fungus Alternaria brassicicola

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Acibenzolar-S-Methyl Reprograms Apple Transcriptome Toward Resistance to Rosy Apple Aphid

International audienceAcibenzolar-S-methyl (ASM) is a chemical compound, which is able to induce resistance in several model and non-model plants, but the end-players of this induced defense remain ill-defined. Here, we test the hypothesis that treatment with ASM can protect apple (Malus × domestica) against the rosy apple aphid (Dysaphis plantaginea) and investigate the defense molecules potentially involved in resistance. We measured aphid life traits and performed behavioral assays to study the effect of ASM on plant resistance against the aphid, and then combined transcriptomic, bioinformatics, metabolic and biochemical analyses to identify the plant compounds involved in resistance. Plants treated with ASM negatively affected several life traits of the aphid and modified its feeding and host seeking behaviors. ASM treatment elicited up-regulation of terpene synthase genes in apple and led to the emission of (E,E)-α-farnesene, a sesquiterpene that was repellent to the aphid. Several genes encoding amaranthin-like lectins were also strongly up-regulated upon treatment and the corresponding proteins accumulated in leaves, petioles and stems. Our results link the production of specific apple proteins and metabolites to the antibiosis and antixenosis effects observed against Dysaphis plantaginea, providing insight into the mechanisms underlying ASM-induced herbivore resistance

Characterization of NRPS and PKS genes involved in the biosynthesis of SMs in Alternaria dauci including the phytotoxic polyketide aldaulactone

International audienceAbstract Alternaria dauci is a Dothideomycete fungus, causal agent of carrot leaf blight. As a member of the Alternaria genus, known to produce a lot of secondary metabolite toxins, A. dauci is also supposed to synthetize host specific and non-host specific toxins playing a crucial role in pathogenicity. This study provides the first reviewing of secondary metabolism genetic basis in the Alternaria genus by prediction of 55 different putative core genes. Interestingly, aldaulactone, a phytotoxic benzenediol lactone from A. dauci , was demonstrated as important in pathogenicity and in carrot partial resistance to this fungus . As nothing is known about aldaulactone biosynthesis, bioinformatic analyses on a publicly available A. dauci genome data set that were reassembled, thanks to a transcriptome data set described here, allowed to identify 19 putative secondary metabolism clusters. We exploited phylogeny to pinpoint cluster 8 as a candidate in aldaulactone biosynthesis. This cluster contains AdPKS7 and AdPKS8 , homologs with genes encoding a reducing and a non-reducing polyketide synthase. Clusters containing such a pair of PKS genes have been identified in the biosynthesis of resorcylic acid lactones or dihydroxyphenylacetic acid lactones. AdPKS7 and AdPKS8 gene expression patterns correlated with aldaulactone production in different experimental conditions. The present results highly suggest that both genes are responsible for aldaulactone biosynthesis