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Stressful environmental conditions lead to the production of reactive oxygen species in the chloroplasts, due to limited photosynthesis and enhanced excitation pressure on the photosystems. Among these reactive species, singlet oxygen (¹O₂), which is generated at the level of the PSII reaction center, is very reactive, readily oxidizing macromolecules in its immediate surroundings, and it has been identified as the principal cause of photooxidative damage in plant leaves. The two β-carotene molecules present in the PSII reaction center are prime targets of ¹O₂ oxidation, leading to the formation of various oxidized derivatives. Plants have evolved sensing mechanisms for those PSII-generated metabolites, which regulate gene expression, putting in place defense mechanisms and alleviating the effects of PSII-damaging conditions. A new picture is thus emerging which places PSII as a sensor and transducer in plant stress resilience through its capacity to generate signaling metabolites under excess light energy. This review summarizes new advances in the characterization of the apocarotenoids involved in the PSII-mediated stress response and of the pathways elicited by these molecules, among which is the xenobiotic detoxification.

• Autophagy is an evolutionarily conserved degradation pathway in the cytoplasm and has emerged as a key defense mechanism against invading pathogens. However, there is no evidence showing nuclear autophagy in plants. • Here, we show that a geminivirus nuclear protein, C1 of tomato leaf curl Yunnan virus (TLCYnV) induces autophagy and interacts directly with the core autophagy-related protein ATG8h. The interaction between ATG8h and C1 leads to the translocation of the C1 protein from the nucleus to the cytoplasm and the decreased protein accumulation of C1, which is dependent on the exportin1-mediated nuclear export pathway. The degradation of C1 is blocked by autophagy inhibitors and compromised when the autophagy-related genes (ATGs) ATG8h, ATG5, or ATG7 are knocked down. Similarly, silencing of these ATGs also promotes TLCYnV infection in Nicotiana benthamiana and Solanum lycopersicum plants. • The mutation of a potential ATG8 interacting motif (AIM) in C1 abolishes its interaction with ATG8h in the cytoplasm but favors its interaction with Fibrillarin1 in the nucleolus. TLCYnV carrying the AIM mutation displays enhanced pathogenicity in solanaceous plants. • Taken together, these data suggest that a new type of nuclear autophagy-mediated degradation of viral proteins through an exportin1-dependent nuclear export pathway restricts virus infection in plants.

Biofloc is a conglomeric aggregation of microbial communities such as phytoplankton, bacteria, and living and dead particulate organic matter. Biofloc technology involves manipulation of C/N ratio to convert toxic nitrogenous wastes into the useful microbial protein and helps in improving water quality under a zero water exchange system. It may act as a complete source of nutrition for aquatic organisms, along with some bioactive compounds that will enhance growth, survival, and defense mechanisms, and acts as a novel approach for health management in aquaculture by stimulating innate immune system of animals. Nutritionally, the floc biomass provides a complete source of nutrition as well as various bioactive compounds that are useful for improving the overall welfare indicators of aquatic organisms. Beneficial microbial bacterial floc and its derivative compounds such as organic acids, polyhydroxy acetate and polyhydroxy butyrate, could resist the growth of other pathogens, thus serves as a natural probiotic and immunostimulant. The technology is useful in maintaining optimum water quality parameters under a zero water exchange system, thus prevents eutrophication and effluent discharge into the surrounding environment. Moreover, the technology will be useful to ensure biosecurity, as there is no water exchange except sludge removal. The technology is economically viable, environmentally sustainable, and socially acceptable.

• Algal viruses are important contributors to carbon cycling, recycling nutrients and organic material through host lysis. Although viral infection has been described as a primary mechanism of phytoplankton mortality, little is known about host defense responses. • We show that viral infection of the bloom-forming, planktonic diatom Chaetoceros socialis induces the mass formation of resting spores, a heavily silicified life cycle stage associated with carbon export due to rapid sinking. • Although viral RNA was detected within spores, mature virions were not observed. ‘Infected’ spores were capable of germinating, but did not propagate or transmit infectious viruses. • These results demonstrate that diatom spore formation is an effective defense strategy against viral-mediated mortality. They provide a possible mechanistic link between viral infection, bloom termination, and mass carbon export events and highlight an unappreciated role of viruses in regulating diatom life cycle transitions and ecological success.

Pathogens use effectors to suppress host defence mechanisms, promote the derivation of nutrients, and facilitate infection within the host plant. Much is now known about effectors that target biotic pathways, particularly those that interfere with plant innate immunity. By contrast, an understanding of how effectors manipulate nonimmunity pathways is only beginning to emerge. Here, we focus on exciting new insights into effectors that target abiotic stress adaptation pathways, tampering with key functions within the plant to promote colonization. We critically assess the role of various signalling agents in linking different pathways upon perturbation by pathogen effectors. Additionally, this review provides a summary of currently known bacterial, fungal, and oomycete pathogen effectors that induce biotic and abiotic stress responses in the plant, as a first step towards establishing a comprehensive picture for linking effector targets to pathogenic lifestyles.

Mosquito-borne diseases are associated with major global health burdens. Aedes spp. and Culex spp. are primarily responsible for the transmission of the most medically important mosquito-borne viruses, including dengue virus, West Nile virus and Zika virus. Despite the burden of these pathogens on human populations, the interactions between viruses and their mosquito hosts remain enigmatic. Viruses enter the midgut of a mosquito following the mosquito’s ingestion of a viremic blood meal. During infection, virus recognition by the mosquito host triggers their antiviral defense mechanism. Of these host defenses, activation of the RNAi pathway is the main antiviral mechanism, leading to the degradation of viral RNA, thereby inhibiting viral replication and promoting viral clearance. However, whilst antiviral host defense mechanisms limit viral replication, the mosquito immune system is unable to effectively clear the virus. As such, these viruses can establish persistent infection with little or no fitness cost to the mosquito vector, ensuring life-long transmission to humans. Understanding of the mosquito innate immune response enables the discovery of novel antivectorial strategies to block human transmission. This review provides an updated and concise summary of recent studies on mosquito antiviral immune responses, which is a key determinant for successful virus transmission. In addition, we will also discuss the factors that may contribute to persistent infection in mosquito hosts. Finally, we will discuss current mosquito transmission-blocking strategies that utilize genetically modified mosquitoes and Wolbachia- infected mosquitoes for resistance to pathogens.

In the carnivorous plant Venus flytrap (Dionaea muscipula), the sequence of events after prey capture resembles the well-known plant defence signalling pathway in response to pathogen or herbivore attack. Here, we used wounding to mimic prey capture to show the similarities and differences between botanical carnivory and plant defence mechanisms. We monitored movement, electrical signalling, jasmonate accumulation and digestive enzyme secretion in local and distal (systemic) traps in response to prey capture, the mechanical stimulation of trigger hairs and wounding. The Venus flytrap cannot discriminate between wounding and mechanical trigger hair stimulation. Both induced the same action potentials, rapid trap closure, hermetic trap sealing, the accumulation of jasmonic acid (JA) and its isoleucine conjugate (JA-Ile), and the secretion of proteases (aspartic and cysteine proteases), phosphatases and type I chitinase. The jasmonate accumulation and enzyme secretion were confined to the local traps, to which the stimulus was applied, which correlates with the propagation of electrical signals and the absence of a systemic response in the Venus flytrap. In contrast to plant defence mechanisms, the absence of a systemic response in carnivorous plant may represent a resource-saving strategy. During prey capture, it could be quite expensive to produce digestive enzymes in the traps on the plant without prey.

1. Tail autotomy is mainly considered an antipredator mechanism. Theory suggests that predation pressure relaxes on islands, subsequently reducing autotomy rates. 2. Intraspecific aggression, which may also cause tail loss, probably intensifies on islands due to the higher abundance. 3. We studied whether tail autotomy is mostly affected by predation pressure or by intraspecific competition. We further studied whether predator abundance or predator richness is more important in this context. 4. To test our predictions, we examined multiple populations of two gecko species: Kotschy's gecko (Mediodactylus kotschyi; mainland and 41 islands) and the Mediterranean house gecko (Hemidactylus turcicus; mainland and 17 islands), and estimated their abundance together with five indices of predation. 5. In both species, autotomy rates are higher on islands and decline with most prédation indices, in contrast with common wisdom, and increase with gecko abundance. In M. kotschyi, tail-loss rates are higher on predator and viper-free islands, but increase with viper abundance. 6. We suggest that autotomy is not simply, or maybe even mainly, an antipredatory mechanism. Rather, such defence mechanisms are a response to complex direct and indirect biotic interactions and perhaps, in the case of tail autotomy in insular populations, chiefly to intraspecific aggression.

Tree resistance can be enhanced by a variety of biotic and abiotic inducers, including nonpathogenic and pathogenic microbes, and herbivores, resulting in enhanced protection against further biotic injury. Induced resistance (IR) could be a valuable tool in sustainable pest management. IR has been actively studied in herbaceous plant species, and, in recent years, in woody plant species, and is fast emerging as an intriguing, eco-friendly concept for enhancing tree resistance. However, before application of IR becomes possible, there is a need to increase our knowledge of the mechanisms of defence in forest trees. A richer understanding of these phenomena will play a critical role in developing sustainable integrated pest management strategies. This review summarizes our current knowledge of IR in forest trees, focusing on inducible defence mechanisms, systemic induction of resistance and phytohormone signalling networks. We conclude by discussing the potential advantages and limitations of applying IR-based management tools in forest systems.

• Vitellogenin (Vg) is a well-known nutritious protein involved in reproduction in nearly all oviparous animals, including insects. Recently, Vg has been detected in saliva proteomes of several piercing–sucking herbivorous arthropods, including the small brown planthopper (Laodelphax striatellus, SBPH). Its function, however, remains unexplored. • We investigated the molecular mechanism underlying SBPH orally secreted Vg-mediated manipulation of plant–insect interaction by RNA interference, phytohormone and H₂O₂ profiling, protein–protein interaction studies and herbivore bioassays. • A C-terminal polypeptide of Vg (VgC) in SBPH, when secreted into rice plants, acted as a novel effector to attenuate host rice defenses, which in turn improved insect feeding performance. Silencing Vg reduced insect feeding and survival on rice. Vg-silenced SBPH nymphs consistently elicited higher H₂O₂ production, a well-established defense mechanism in rice, whereas expression of VgC in planta significantly hindered hydrogen peroxide (H₂O₂) accumulation and promoted insect performance. VgC interacted directly with the rice transcription factor OsWRKY71, a protein which is involved in induction of H₂O₂ accumulation and plant resistance to SBPH. • These findings indicate a novel effector function of Vg: when secreted into host rice plants, this protein effectively weakened H₂O₂-mediated plant defense through its association with a plant immunity regulator.