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Aerobic living is thought to generate reactive oxygen species (ROS), which are an inevitable chemical component. They are produced exclusively in cellular compartments in aerobic metabolism involving significant energy transfer and are regarded as by-products. ROS have a significant role in plant response to pathogenic stress, but the pattern varies between necrotrophs and biotrophs. A fine-tuned systemic induction system is involved in ROS-mediated disease development in plants. In regulated concentrations, ROS act as a signaling molecule and activate different pathways to suppress the pathogens. However, an excess of these ROS is deleterious to the plant system. Along with altering cell structure, ROS cause a variety of physiological reactions in plants that lower plant yield. ROS also degrade proteins, enzymes, nucleic acids, and other substances. Plants have their own mechanisms to overcome excess ROS and maintain homeostasis. Microbes, especially endophytes, have been reported to maintain ROS homeostasis in both biotic and abiotic stresses by multiple mechanisms. Endophytes themselves produce antioxidant compounds and also induce host plant machinery to supplement ROS scavenging. The structured reviews on how endophytes play a role in ROS homeostasis under biotic stress were very meager, so an attempt was made to compile the recent developments in ROS homeostasis using endophytes. This review deals with ROS production, mechanisms involved in ROS signaling, host plant mechanisms in alleviating oxidative stress, and the roles of endophytes in maintaining ROS homeostasis under biotic stress.

For the burgeoning global population, sustainable agriculture practices are crucial for accomplishing the zero-hunger goal. The agriculture sector is very concerned about the rise in insecticide resistance and the Modern Environmental Health Hazards (MEHHs) that are problems for public health due to on pesticide exposure and residues. Currently, farming practices are being developed based on microbial bio-stimulants, which have fewer negative effects and are more efficient than synthetic agro-chemicals. In this context, one of the most important approaches in sustainable agriculture is the use of biocontrol microbes that can suppress phytopathogens and insects. Simultaneously, it is critical to comprehend the role of these microbes in promoting growth and disease control, and their application as biofertilizers and biopesticides, the success of which in the field is currently inconsistent. Therefore, editorial is part of a special issue titled \"Biocontrol Strategies: An Eco-smart Tool for Integrated Pest and Disease Management\" which focuses on biocontrol approaches that can suppress the biotic stresses, alter plant defense mechanisms, and offer new eco-smart ways for controlling plant pathogens and insect pests under sustainable agriculture.

Induction of defense response in host plants by the Trichoderma spp. has been attributed as one of the major mechanisms leading to inhibition of the pathogenic ingression. The present study sheds light on the mechanisms employed by the Trichoderma isolates, obtained from phyllosphere (BHUF4) and rhizosphere (T16A), to modulate the defense network of chili plant under Colletotrichum truncatum challenge. Plants treated with both the Trichoderma strains exhibited significant accumulation of phenols under C. truncatum challenge with maximum increment recorded for capsaicin (16.1-fold), ferulic acid (5.03-fold), quercetin (5.36-fold), salicylic acid (94.88-fold), and kaempeferol (6.22-fold). Phenol accumulation corresponded to the subsequent defense gene expression pattern. When compared to the pathogen-challenged control plants, enhanced expression of PR1, PIK1, CHI, GLU, Cdef, and SAR genes was recorded in the Trichoderma-treated plants acting as a biocontrol agent (BCA). The results of the present study suggest that to strengthen the defense pathways in the host plant, the mechanisms employed by Trichoderma isolates differ and depend upon their origin and site of application. While phyllospheric Trichoderma isolate (BHUF4) employed the systemic acquired resistance (SAR) pathway, the rhizospheric Trichoderma strain (T16A) used the induced systemic response (ISR) pathway for eliciting the defense response in the host plant under C. truncatum challenge. The study signifies how Trichoderma strains obtained from different origin and when applied at different sites in plant judiciously reprogram the defense network of the host plant to provide robust protection against phytopathogens. In the present case, overall protection is provided to the chili plants against the foliar or underground attack of C. truncatum.

UV-C irradiation is known to enhance plant resistance against insect pests. In the present study, we evaluated the effects of low doses of UV-C on Macrosiphum rosae infesting greenhouse rose (Rosa x hybrida) plants. The application of 2.5-kJ/m2 UV-C irradiation on rose leaves before infestation induced anti-herbivore resistance and negatively affected the aphid fecundity. No eggs and first instar nymphs were recorded on irradiated leaves, whereas an average of 4.3 and 2.7 eggs and 6.7 and 14 first instars were recorded on vars. “Etoile Brilante” and “Arlen Francis” untreated leaves, respectively. UV-C irradiation reduced the aphid population from naturally infested rose plants by up to 58%. In a greenhouse pot trial (GPT) in 2019, UV-C irradiation minimised the initial aphid population six hours after treatment. UV-C elicited host resistance and, also, helped in aphid repulsion without killing the adult individuals. UV-C did not affect the physiological responses of rose plants. The net CO2 assimilation of the UV-C irradiated plants ranged between 10.55 and 15.21 μmol/m2. sec for “Arlen Francis” and between 10.51 and 13.75 μmol/m2. sec for “Etoile Brilante” plants. These values, with only a few exceptions, were similar to those recorded to the untreated plants.

Selected soil‐borne rhizobacteria can trigger an induced systemic resistance (ISR) that is effective against a broad spectrum of pathogens. In Arabidopsis thaliana, the root‐specific transcription factor MYB72 is required for the onset of ISR, but is also associated with plant survival under conditions of iron deficiency. Here, we investigated the role of MYB72 in both processes. To identify MYB72 target genes, we analyzed the root transcriptomes of wild‐type Col‐0, mutant myb72 and complemented 35S:FLAG‐MYB72/myb72 plants in response to ISR‐inducing Pseudomonas fluorescens WCS417. Five WCS417‐inducible genes were misregulated in myb72 and complemented in 35S:FLAG‐MYB72/myb72. Amongst these, we uncovered β‐glucosidase BGLU42 as a novel component of the ISR signaling pathway. Overexpression of BGLU42 resulted in constitutive disease resistance, whereas the bglu42 mutant was defective in ISR. Furthermore, we found 195 genes to be constitutively upregulated in MYB72‐overexpressing roots in the absence of WCS417. Many of these encode enzymes involved in the production of iron‐mobilizing phenolic metabolites under conditions of iron deficiency. We provide evidence that BGLU42 is required for their release into the rhizosphere. Together, this work highlights a thus far unidentified link between the ability of beneficial rhizobacteria to stimulate systemic immunity and mechanisms induced by iron deficiency in host plants.

The processes of morphogenesis and differentiation are crucial for leaf development, with the duration of the morphogenetic window influencing final leaf shape. Leaves at different developmental stages exhibit distinct morphological and physiological characteristics that may influence their ability to resist pathogens, and disease resistance has been linked to developmental stage in many plant species. To understand how leaf development impacts disease resistance, we examined the immunity of leaves at distinct developmental stages, exploring the role of hormonal pathways and the impact of leaf structure and microbial interactions on disease resistance. Our findings reveal that leaves of different developmental stages exhibit distinct disease responses to various pathogens, determined primarily by the ratio between salicylic acid and jasmonic acid. Higher relative jasmonic acid content in later developing leaves was found to result in increased disease resistance to necrotrophs, while higher relative salicylic acid content in earlier developing leaves rendered them more resistant to biotrophs. This phenomenon occurred across plant ages, in several species, and also impacted the plants' response to biocontrol agents, depending on the pathway being primed. We found that structural variations among leaves can also affect disease response, due to differential recognition by the invading pathogen, and possibly also due to alterations in the leaf microbiome. Our results uncover some of the factors influencing developmental immunity in tomato, and highlight the importance of considering plant development when managing disease resistance. To understand how leaf development impacts disease resistance, we examined the immunity of leaves at distinct developmental stages, exploring the role of hormonal pathways and leaf structure. Our findings reveal that distinct disease responses of different developmental staged leaves are determined primarily by the ratio between salicylic acid and jasmonic acid.

[...]Junget al.reviewed the systemic plant defense signaling induced by beneficial microbes as an alternative approach for pathogen suppression instead of direct microbe- microbe interactions. Future research needs to deepen our knowledge to optimize microbiome-based disease management by integrating microbial consortia, synthetic biology, and precision agriculture technologies to take advantage of the microbes’ full potential. Conflict of interest The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Bacillus subtilis 26D is a plant growth-promoting endophytic bacteria capable of inducing systemic resistance through the priming mechanism, which includes plant genome reprogramming and the phenomenon of RNA interference (RNAi) and microRNA (miRNAs). The phloem-feeding insect bird cherry-oat aphid Rhopalosiphum padi L. is a serious pest that causes significant damage to crops throughout the world. However, the function of plant miRNAs in the response to aphid infestation remains unclear. The results of this work showed that B. subtilis 26D stimulated aphid resistance in wheat plants, inducing the expression of genes of hormonal signaling pathways ICS, WRKY13, PR1, ACS, EIN3, PR3, and ABI5. In addition, B. subtilis 26D activated the RNAi mechanism and regulated the expression of nine conserved miRNAs through activation of the ethylene, salicylic acid (SA), and abscisic acid (ABA) signaling pathways, which was demonstrated by using treatments with phytohormones. Treatment of plants with SA, ethylene, and ABA acted in a similar manner to B. subtilis 26D on induction of the expression of the AGO4, AGO5 and DCL2, DCL4 genes, as well as the expression of nine conserved miRNAs. Different patterns of miRNA expression were found in aphid-infested plants and in plants treated with B. subtilis 26D or SA, ethylene, and ABA and infested by aphids, suggesting that miRNAs play multiple roles in the plant response to phloem-feeding insects, associated with effects on hormonal signaling pathways, redox metabolism, and the synthesis of secondary metabolites. Our study provides new data to further elucidate the fine mechanisms of bacterial-induced priming. However, further extensive work is needed to fully unravel these mechanisms.

The use of beneficial rhizobacteria (bioeffectors) and their derived metabolic elicitors are efficient biotechnological alternatives in plant immune system elicitation. This work aimed to check the ability of 25 bacterial strains isolated from the rhizosphere of Nicotiana glauca, and selected for their biochemical traits from a group of 175, to trigger the innate immune system of Arabidopsis thaliana seedlings against the pathogen Pseudomonas syringae pv. tomato DC3000. The five strains more effective in preventing pathogen infection were used to elucidate signal transduction pathways involved in the plant immune response by studying the differential expression of Salicylic acid and Jasmonic acid/Ethylene pathway marker genes. Some strains stimulated both pathways, while others stimulated either one or the other. The metabolic elicitors of two strains, chosen for the differential expression results of the genes studied, were extracted using n-hexane, ethyl acetate, and n-butanol, and their capacity to mimic bacterial effect to trigger the plant immune system was studied. N-hexane and ethyl acetate were the most effective fractions against the pathogen in both strains, achieving similar protection rates although gene expression responses were different from that obtained by the bacteria. These results open an amount of biotechnological possibilities to develop biological products for agriculture.

New insights into the phenomenon of systemic acquired resistance have been gained in recent years, by the use of techniques in molecular genetics and biology that have replaced the largely descriptive approach of earlier work. The isolation of mutants in the signal transduction pathway from induction to expression of resistance as well as the use of transgenic plants over-expressing or suppressing the expression of putative candidate genes involved in systemic acquired resistance and its signalling have identified several steps in the establishment of plant resistance. In this review the latest developments implicating salicylic acid as a signal molecule in systemic resistance are discussed and contrasted with new signalling pathways which, seemingly, are based on alternative mechanisms.