Arteriviruses are one of 14 families that make up the highly diverse order of positive-stranded RNA viruses known as the Nidovirales. Certain members of this family, such as Equine Arterivirus (EAV) and Porcine Reproductive and Respiratory Syndrome Virus (PPRSV) represent significant animal pathogens which present a large economic burden. However they have been relatively understudied, especially in comparison with viruses of the related Coronaviridae (CoV) family (notably SARS-CoV-2), which have attracted significant attention over the past few years. This project was aimed at bridging this knowledge-gap, by investigating key arterivirus viral enzymes: including the RNA-dependent RNA polymerase (RdRp) and its unique N−terminal domain, known as the NiRAN. These two enzymes are at the center of the viral replication transcription complex (RTC), responsible for copying and amplifying the genomic information for passage to progeny virions. As such, they represent extremely attractive antiviral targets. The project, which is still ongoing, involves the structural and functional characterization of these two essential enzymes for viruses of the Arteriviridae family. This will expand our understanding of understudied viruses with epidemic potential, and guide drug design strategies against key viral targets.

Water scarcity in agriculture is worsening, leading to plant drought stress with direct impacts on physiology and productivity. Abscisic acid (ABA), a key plant stress hormone, plays a central role in drought response pathways. Recent research has revealed that nicotinamide adenine dinucleotide (NAD), a metabolic cofactor, is also involved in drought stress. Plants impaired in NAD metabolism display differential drought responses depending on NAD⁺ content with a direct correlation with ABA levels and signaling. However, the mechanisms underlying the NAD-ABA interaction and its validation as essential for plant responses to drought remain to be explored. The project explores the connection between plant metabolism and hormone signaling, with a focus on its consequences in drought responses. Through a combination of genetics, physiology, and metabolic approaches, we aim to gain fresh insights into the regulation of the interaction between the metabolic cofactor NAD and the plant stress hormone ABA.

2,4-diacetylphloroglucinol (DAPG) is a potent fungicide produced by Pseudomonas isolates (https://doi.org/10.3389/fmicb.2017.01218). Indeed, suppression of Take-all disease, caused by the ascomycete Gaeumannomyces graminis var. tritici, in disease suppressive soils has been repeatedly associated with an increased abundance of DAPG-producing bacterial strains (https://doi.org/10.1016/j.soilbio.2012.05.012). Accordingly, DAPG-producing bacteria have potential as biocontrol agents. In this project, we aimed to evaluate the direct use of DAPG as a biosourced fungicide to circumvent drawbacks of products based on living bacteria.

A major aim was to investigate possible bioproduction of DAPG. To identify a suitable bacterial chassis, we screened twenty-one Pseudomonas strains, selected from a previous large-scale screen, for antifungal properties. We showed, by mutations in the gene coding for the enzyme catalyzing the committing step in DAPG biosynthesis, phlD, that antifungal properties in three best-performing strains were based on DAPG production. We further improved DAPG production, by approximately a factor four, by inactivation of a repressor (PhlF) and a hydrolase (PhlG). In yet another approach to manipulate DAPG production, we designed and assembled a synthetic gene cluster encompassing the phl genes for DAPG biosynthesis. The synthetic gene cluster, when inserted into a non DAPG-producing Pseudomonas strain, confers antifungal properties. The modular design of the synthetic cluster will allow us to further manipulate DAPG production and content, as promoters driving individual transcription units can be exchanged with ease following standardized assembly reactions. Last, we assayed DAPG biocontrol capacities in plate assays, and observed that DAPG doses efficient as fungicide (≥ 20 µM) also impede plant growth and development. Considering the natural biocontrol capacities of DAPG-producing bacteria in the field, we will address the feasibility and efficacy of DAPG in seed coatings to protect from fungal diseases in the future.

The OM-PSG project investigates the role of Msr (Methionine Sulfoxide Reductase) enzymes in bacterial responses to oxidative stress. By combining fluorescence microscopy at the single-cell level with microfluidic tools, this project aims at gaining deeper insights into bacterial stress responses and repair mechanisms under oxidative conditions.

The originality of this research lies in the dynamic study of these enzymes under controlled conditions, enabling real-time observation of their role in bacterial physiology. Through the technological developments implemented, the project opens new interdisciplinary perspectives and strengthens collaborations in advanced imaging and oxidative stress biology.

This work is part of a broader effort to decipher bacterial adaptation strategies to oxidative environments and is supported by IM2B for the development of innovative approaches.