How can plant defences lead to valuable products? Inspiration from plant complexity in phytochemistry

International audienceIf plants are known for centuries as a valuable source of molecules, complexity remains and can open up numerous perspectives. Plants have indeed evolved a wide range of secondary metabolites as defense, competition or attraction compounds [1]. More particularly, the exceptional biodiversity encountered in the tropics, along with the presence of various pathogens and a strong herbivory especially linked to a rich entomofauna, leads to a promising chemodiversity, due to the constant and dynamic interactions between plants and their environment. Taking into account the role and “raison d'être”[2] of natural products, and the fact that all these molecules work together as complex mixtures can therefore lead to a new point of view, by shifting from the “magic bullet” classical approach to a “herbal shotgun” strategy[3]. We will illustrate the fact that, inspired by their ecological functions, and taking into account synergistic interactions, some therapeutic applications can be found for these versatile mixtures of compounds. In particular we examined whether the antidermatophytic activity of essential oils (EOs) obtained from particularly fragrant plant species from French Guiana could be used as an indicator for the discovery of active natural products against Leishmania amazonensis. A significant correlation was observed between antidermatophytic and antileishmanial activity, confirming the “alternative use” strategy in the case of EOs, and allowed us to highlight P. hispidum Sw. (Piperaceae) EO as a promising antileishmanial product [4]. We also illustrated the importance of synergistic effects through the example of the antifungal EO of Otacanthus azureus (Linden) Ronse (Plantaginaceae) [5] and the biomimetic design of optimized synergistic mixtures thanks to a full factorial experiment approach

Adaptability of myosin V studied by simultaneous detection of position and orientation

We studied the structural dynamics of chicken myosin V by combining the localization power of fluorescent imaging with one nanometer accuracy (FIONA) with the ability to detect angular changes of a fluorescent probe. The myosin V was labeled with bifunctional rhodamine on one of its calmodulin light chains. For every 74 nm translocation, the probe exhibited two reorientational motions, associated with alternating smaller and larger translational steps. Molecules previously identified as stepping alternatively 74-0 nm were found to actually step 64-10 nm. Additional tilting often occurred without full steps, possibly indicating flexibility of the attached myosin heads or probing of their vicinity. Processive myosin V molecules sometimes shifted from the top to the side of actin, possibly to avoid an obstacle. The data indicate marked adaptability of this molecular motor to a nonuniform local environment and provide strong support for a straight-neck model of myosin V in which the lever arm of the leading head is tilted backwards at the prepowerstoke angle