Weapons against Themselves: Identification and Use of Quorum Sensing Volatile Molecules to Control Plant Pathogenic Fungi Growth.

Quorum sensing (QS) is often defined as a mechanism of microbial communication that can regulate microbial behaviors in accordance with population density. Much is known about QS mechanisms in bacteria, but fungal QS research is still in its infancy. In this study, the molecules constituting the volatolomes of the plant pathogenic fungi Fusarium culmorum and Cochliobolus sativus have been identified during culture conditions involving low and high spore concentrations, with the high concentration imitating overpopulation conditions (for QS stimulation). We determined that volatolomes emitted by these species in conditions of overpopulation have a negative impact on their mycelial growth, with some of the emitted molecules possibly acting as QSM. Candidate VOCs related to QS have then been identified by testing the effect of individual volatile organic compounds (VOCs) on mycelial growth of their emitting species. The antifungal effect observed for the volatolome of F. culmorum in the overpopulation condition could be attributed to ethyl acetate, 2-methylpropan-1-ol, 3-methylbutyl ethanoate, 3-methylbutan-1-ol, and pentan-1-ol, while it could be attributed to longifolene, 3-methylbutan-1-ol, 2-methylpropan-1-ol, and ethyl acetate for C. sativus in the overpopulation condition. This work could pave the way to a sustainable alternative to chemical fungicides.

Linoleic and linolenic acid hydroperoxides interact differentially with biomimetic plant membranes in a lipid specific manner.

Linoleic and linolenic acid hydroperoxides (HPOs) constitute key intermediate oxylipins playing an important role as signaling molecules during plant defense processes in response to biotic or abiotic stress. They have also been demonstrated in vitro as antimicrobial agents against plant fungi and bacteria. To reach the phytopathogens in vivo, the HPOs biosynthesized in the plant cells must cross the plant plasma membrane (PPM) where they can also interact with plasma membrane lipids and have an effect on their organization. In the present study, we have investigated the interaction properties of HPOs with PPM at a molecular level using biophysical tools combining in vitro and in silico approaches and using plant biomimetic lipid systems. Our results have shown that HPOs are able to interact with PPM lipids and perturb their lateral organization. Glucosylceramide (GluCer) is a privileged partner, sitosterol lessens their binding and the presence of both GluCer and sitosterol further reduces their interaction. Hydrophobic effect and polar interactions are involved in the binding. The chemical structure of HPOs influences their affinity for PPM lipids. The presence of three double bonds in the HPO molecule gives rise to a higher affinity comparatively to two double bonds, which can be explained by their differential interaction with the lipid polar headgroups.

First Characterisation of Volatile Organic Compounds Emitted by Banana Plants.

Banana (Musa sp.) ranks fourth in term of worldwide fruit production, and has economical and nutritional key values. The Cavendish cultivars correspond to more than 90% of the production of dessert banana while cooking cultivars are widely consumed locally around the banana belt production area. Many plants, if not all, produce Volatile Organic Compounds (VOCs) as a means of communication with their environment. Although flower and fruit VOCs have been studied for banana, the VOCs produced by the plant have never been identified despite their importance in plant health and development. A volatile collection methodology was optimized to improve the sensitivity and reproducibility of VOCs analysis from banana plants. We have identified 11 VOCs for the Cavendish, mainly (E,E)-α-farnesene (87.90 ± 11.28 ng/µl), methyl salicylate (33.82 ± 14.29) and 6-methyl-5-hepten-2-one (29.60 ± 11.66), and 14 VOCs for the Pacific Plantain cultivar, mainly (Z,E)-α-farnesene (799.64 ± 503.15), (E,E)-α-farnesene (571.24 ± 381.70) and (E) ß ocimene (241.76 ± 158.49). This exploratory study paves the way for an in-depth characterisation of VOCs emitted by Musa plants.

Current impact and future directions of high throughput sequencing in plant virus diagnostics.

The ability to provide a fast, inexpensive and reliable diagnostic for any given viral infection is a key parameter in efforts to fight and control these ubiquitous pathogens. The recent developments of high-throughput sequencing (also called Next Generation Sequencing - NGS) technologies and bioinformatics have drastically changed the research on viral pathogens. It is now raising a growing interest for virus diagnostics. This review provides a snapshot vision on the current use and impact of high throughput sequencing approaches in plant virus characterization. More specifically, this review highlights the potential of these new technologies and their interplay with current protocols in the future of molecular diagnostic of plant viruses. The current limitations that will need to be addressed for a wider adoption of high-throughput sequencing in plant virus diagnostics are thoroughly discussed.

Identification of genes involved in the response of banana to crown rot disease.

Variations in banana susceptibility to crown rot disease have been observed but the molecular mechanisms underlying these quantitative host-pathogen relationships are still unknown. This study was designed to compare gene expression between crowns of banana fruit showing a high susceptibility (S(+)) and crowns showing a low susceptibility (S(-)) to the disease. Comparisons were performed at two situation times: i) between crowns (S(+) and S(-)) collected 1 h before inoculation and ii) between crowns (S+ and S-) collected 13 days after inoculation. Gene expression comparisons were performed with cDNA-amplified fragment length polymorphism (AFLP) and results were confirmed by real-time reverse-transcription polymerase chain reaction. Among genes identified as differentially expressed between S(+) and S(-) crowns, two were involved in signal transduction, three in proteolytic machinery, two had similarity to pathogenesis-related protein 14, one to a CCR4-associated factor protein, and one to a cellulose synthase. Paradoxically, the overexpression of the cellulose synthase gene was associated with banana showing a high susceptibility in both pre- and post-inoculation situations. Finally, the cDNA-AFLP identified a gene that seems to be associated with the quantitative banana responses to crown rot disease; this gene encodes a dopamine-ß-monooxygenase, which is involved in the catecholamine pathway. To our knowledge, this work is the first to address both pre- and post-infection gene expression with the same host-pathogen combination and distinct susceptibility levels.

Use of molecular techniques to elucidate the mechanisms of action of fungal biocontrol agents: a review.

Biological control of fungal plant pathogens appears as an attractive and realistic approach, and numerous microorganisms have been identified as biocontrol agents. There have been many efforts to understand the mechanisms of action of fungal biocontrol agents. Microbiological, microscopic, and biochemical techniques applied over many years have shed light on these mechanisms without fully demonstrating them. More recently, the development of molecular techniques has yielded innovative alternative tools for understanding and demonstrating the mechanisms underlying biocontrol properties. To date, more than 70 publications describe the use of molecular techniques for this purpose. They describe work exploiting targeted or non-targeted gene isolation, gene expression profiling, gene inactivation and/or overexpression, the study of regulatory factors. This work has shed considerable light on mechanisms underlying biocontrol properties. It has also fully demonstrated a number of targeted action mechanisms of some biocontrol agents. This review describes the techniques used in such studies, with their potential and limitations. It should provide a guide for researchers wanting to study the molecular basis of the biocontrol in diverse biocontrol agents.