Siderophores are specific ferric iron chelators synthesized by virtually all microorganisms in response to iron deficiency. We have previously shown that they promote infection by the phytopathogenic enterobacteria Dickeya dadantii and Erwinia amylovora. Siderophores also have the ability to activate plant immunity. We have used complete Arabidopsis transcriptome microarrays to investigate the global transcriptional modifications in roots and leaves of Arabidopsis (Arabidopsis thaliana) plants after leaf treatment with the siderophore deferrioxamine (DFO). Physiological relevance of these transcriptional modifications was validated experimentally. Immunity and heavy-metal homeostasis were the major processes affected by DFO. These two physiological responses could be activated by a synthetic iron chelator ethylenediamine-di(o-hydroxyphenylacetic) acid, indicating that siderophores eliciting activities rely on their strong iron-chelating capacity. DFO was able to protect Arabidopsis against the pathogenic bacterium Pseudomonas syringae pv tomato DC3000. Siderophore treatment caused local modifications of iron distribution in leaf cells visible by ferrocyanide and diaminobenzidine-H 2 O 2 staining. Metal quantifications showed that DFO causes a transient iron and zinc uptake at the root level, which is presumably mediated by the metal transporter iron regulated transporter1 (IRT1). Defense gene expression and callose deposition in response to DFO were compromised in an irt1 mutant. Consistently, plant susceptibility to D. dadantii was increased in the irt1 mutant. Our work shows that iron scavenging is a unique mechanism of immunity activation in plants. It highlights the strong relationship between heavy-metal homeostasis and immunity.

Natural products containing non-tetramic gamma-hydroxy-gamma-lactams and gamma-alkylidene-gamma-lactams are usually but not exclusively derived from the mixed polyketide-non-ribosomal peptide biosynthetic pathway. Often they are fungal metabolites, although some plant- and marine-derived exceptions exist. Owing to their unique structures and biological properties, they have gained interest in the chemical and biological communities. In this review, we aim to emphasize the structural originality of these compounds, their biological properties and the synthetic efforts developed to reach them; 157 references are cited.

The authors noticed that Scheme 1i ntheir Full Paper was incorrectly drawn. The correct Scheme 1 is provided below.The authors apologize for the oversight. Scheme 1. Postulated mechanism for cyclohexadecane formation from cyclooctanem etathesis.

Extensive solid-state NMR analyses unambiguously determine the formation of silica supported W bis-methylidene methyl species by reaction of the corresponding methyl carbyne with trimethylphosphine or a cyclic olefin.

A method for the total synthesis of naturally occurring 3-enoyltetramic acids derived from L-tyrosine is described, allowing for three chemical transformations to occur in one pot by using a multicomponent mixture. The sequence involves (1) a base-promoted Lacey-Dieckmann condensation, (2) a Michaelis-Becker reaction, and (3) a Wittig-Horner-Emmons reaction between the resulting 3-phosphonoacetyltetramic

The activity of silica-supported tungsten carbyne complexes (≡SiO)xW(≡CH)(Me)y (x = 1, y = 2; x = 2, y = 1) toward alkynes is reported. We found that they are efficient precatalysts for terminal alkyne cyclotrimerization with high TONs. We also demonstrate that this catalyst species is active for alkyne cyclotrimerization without the formation of significant alkyne metathesis products. Additional DFT calculations highlight the importance of the W coordination sphere in supporting this experimental behaviorA.P. thanks the Spanish MINECO for a Ramón y Cajal contract (RYC-2009-05226) and the European Commission for a Career Integration Grant (CIG09-GA-2011-293900

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Metathesis of linear alkanes versus olefins using supported multifunctional catalyst gives a very striking different distribution of metathesis products.