Summary: Oomycete phytopathogens have adapted to colonise plants using effectors as their molecular weapons. Intracellular effectors, mostly proteins but also small ribonucleic acids, are delivered by the pathogens into the host cell cytoplasm where they interfere with normal plant physiology. The diverse host processes emerging as ‘victims’ of these ‘specialised bullets’ include gene transcription and RNA‐mediated silencing, cell death, protein stability, protein secretion and autophagy. Some effector targets are directly involved in defence execution, while others participate in fundamental metabolisms whose alteration collaterally affects defences. Other effector targets are susceptibility factors (SFs), that is host components that make plants vulnerable to pathogens. SFs are mostly negative regulators of immunity, but some seem necessary to sustain or promote pathogen colonisation.

Arabidopsis OXIDATION RESISTANCE2 levels influence salicylic acid-mediated defense, increasing plant resistance to pathogen infection.

The search for environmentally friendly solutions to effectively control crop pests while safeguarding human health has become a global priority. One promising strategy is to enhance plant defenses by pre-inducing their innate immune system. In this study, we developed rhamnolipid (RL)-stabilized nanoemulsions (NEs) encapsulating essential oils (EOs) as potential biopesticides and biostimulants for agroindustrial applications. These NEs were designed to improve the solubility and stability of EOs while effectively combining their insecticidal and/or repellent activities with the bioactive properties of RLs. In this regard, our interdisciplinary approach involved formulating and characterizing these NEs and evaluating their stability and wettability on plant leaf surfaces. We further evaluated their effects on bacterial growth in vitro and in the model plant Arabidopsis thaliana, along with their impact on beneficial soil microorganisms. We analyzed their ability to stimulate the plant’s immune system and their impact on the viability and reproduction of the aphid Myzus persicae. Additionally, we explored whether RLs stimulate plant defenses through alterations in the leaf cuticle. Our findings demonstrate that RL-stabilized EO-NEs are effective bioprotectants and biostimulants in the model plant, offering a sustainable alternative that could reduce reliance on chemical pesticides in agriculture.

Plant pathogens and pests can cause significant losses in crop yields, affecting food security and the global economy. Many traditional chemical pesticides are used to combat these organisms. This can lead to the development of pesticide-resistant strains of pathogens/insects and negatively impact the environment. The development of new bioprotectants, which are less harmful to the environment and less likely to lead to pesticide-resistance, appears as a sustainable strategy to increase plant immunity. Natural Rhamnolipids (RL-Nat) are a class of biosurfactants with bioprotectant properties that are produced by an opportunistic human pathogen bacterium. RL-Nat can act as plant resistance inducers against a wide variety of pathogens. Recently, a series of bioinspired synthetic mono-RLs produced by green chemistry were also reported as phytoprotectants. Here, we explored their capacity to generate novel colloidal systems that might be used to encapsulate bioactive hydrophobic compounds to enhance their performance as plant bioprotectants. The synthetic mono-RLs showed good surfactant properties and emulsification power providing stable nanoemulsions capable of acting as bio-carriers with good wettability. Synthetic RLs-stabilized nanoemulsions were more effective than RLs suspensions at inducing plant immunity, without causing deleterious effects. These nanoemulsions were innocuous to native substrate microbiota and beneficial soil-borne microbes, making them promising safe bio-carriers for crop protection.