Hormonal control is of crucial importance for plant development and their adaptation to changing environmental conditions. Molecular genetics combined with biochemical and metabolic approaches have revealed insights into the biosynthesis, transport, perception, and cellular signalling of several plant hormones. Jasmonic acid (JA) is one of such hormones, playing prominent roles in plant reproduction and their constant adaptation to environmental stresses and attacks by insects or microbial pathogens. JA is synthetized from unsaturated fatty acids and its structure is reminiscent of animal prostaglandins. Among numerous JA derivatives that were detected in plant extracts, the JA-Isoleucine (JA-Ile) conjugate has been recognized as an active endogenous ligand of the F-box receptor protein COI1. The current model for JA signalling implies that ligand binding promotes the recruitment of “JAZ” protein transcriptional repressors to be proteolytically degraded by the ubiquitin-proteasome system, resulting in the de-repression of downstream JA-responsive genes. In contrast, elucidating mechanisms for hormonal signal extinction just started to attract interest. Hydroxy- and carboxy-derivatives of JA-Ile with high potential biological significance accumulate subsequently to jasmonate signalling and we proposed that they may reflect modification of the JA-Ile hormonal activity. We have provided recently strong biochemical and genetic evidence that these oxidized derivatives are generated upon wounding by members of the CYP94 family of cytochrome P450 enzymes, and that their formation is a major catabolic route for JA-Ile turnover. Based on our validation of this underlying hypothesis, the global objective of this proposal is to characterize the actors and processes leading to the enzymatic oxidation of jasmonates and their physiological consequences on various jasmonate-regulated responses. More specific aims include i) Characterization of the full catalytic diversity in the Arabidopsis CYP94 enzyme family in terms of oxidation of jasmonate compounds, ii) Investigation of oxidized jasmonate metabolism in newly generated cyp94 mutants upon antimicrobial defense or developmental steps, iii) Determination of the receptor-binding and signalling properties of oxidized JA-Ile derivatives, iv) Enzymatic activity and function elucidation of novel candidate genes/proteins to form unconjugated hydroxy-jasmonates. The proposed strategies should provide a deeper knowledge of the mechanisms that govern jasmonate catabolism and homeostasis for plant defense and development.

Natural products play an important role in cancer therapy since they have led to the development of several clinically useful anti-cancer agents. As cancer is a major public health problem and will become the leading cause of death worldwide in the 21st century, the search for novel drugs possessing a completely new mode of action represents an important challenge for the improvement of cancer therapy. During the quest for new and potent cytotoxic compounds from natural sources and in particular marine organisms, a new complex polyketide was recently isolated from extracts of the marine sponge Hemimycale sp., collected in deep water around Torres islands (Vanuatu) in the South Pacific, by French researchers of the CNRS-Pierre Fabre Laboratories joint unit in association with Institut de Recherche pour le Développement (IRD). This new natural product, called hemicalide, was found to be a potent mitotic blocker and to display high anti-proliferative potency against a panel of cancer cell lines at subnanomolar concentrations. Importantly, immuno-cytochemistry studies revealed that hemicalide acted by destabilizing the alpha/beta microtubule network but the mechanism seemed to be different from that observed with known antimitotic antitubulin agents such as taxoids and Vinca alkaloids. However, the remaining amount of hemicalide was not sufficient to support complementary pharmacological evaluation and since harvesting the natural raw material is impossible, chemical synthesis remains the only alternative way to pursue the research. The high interest of the molecule motivates complementary research in the quest for a potential innovative anti-cancer agent: an efficient synthetic route for complete structure and configurational assignment, the preparation of simplified derivatives and the generation of structural activity relationships (SAR) studies that could lead to new targets or mechanisms of action. The teams of organic chemists at the ESPCI and Université Paris Descartes, in collaboration with the CNRS-Pierre Fabre Laboratories joint unit, have embarked on the adventure of hemicalide and decided to join their efforts and expertise in the field of natural products synthesis to achieve the goal of this challenging research project, as part of an ambitious natural product lead optimization program. For synthetic chemists, hemicalide constitutes an absolutely fascinating target due to its complex structure, the presence of 21 stereocenters embedded in a 46 carbon atoms backbone as well as original delta-lactone subunits. Encouraging preliminary results have already been obtained indicating that the goal of this project can reasonably be attained and motivating the development of efficient and innovative synthetic strategies.