Role of ethylene and light in chitosan-induced local and systemic defence responses of tomato plants

Potato β-aminobutyric acid receptor IBI1 manipulates VOZ1 and VOZ2 transcription factor activity to promote disease resistance

Upon infection with nonpathogenic microorganisms or treatment with natural or synthetic compounds, plants exhibit a more rapid and potent response to both biotic and abiotic stresses. However, the molecular mechanisms behind this phenomenon, known as defense priming, are poorly understood. β-minobutyric acid (BABA) is an endogenous stress metabolite that enhances plant tolerance to various abiotic stresses and primes plant defense responses, providing the ability to resist a variety of pathogens (broad-spectrum resistance). In this study, we identified an aspartyl-tRNA synthetase (AspRS), StIBI1 (named after Arabidopsis IMPAIRED IN BABA-INDUCED IMMUNITY 1 [IBI1]), as a BABA receptor in Solanum tuberosum. We elucidated the regulatory mechanisms by which StIBI1 interacts with two NAC (NAM, ATAF1, 2, and CUC2) transcription factors (TFs), StVOZ1 and StVOZ2 (VASCULAR PLANT ONE ZINC FINGER [VOZ]), to activate BABA-induced resistance (BABA-IR). StVOZ1 represses, whereas StVOZ2 promotes, immunity to the late blight pathogen Phytophthora infestans. Interestingly, BABA and StIBI1 influence StVOZ1- and StVOZ2-mediated immunity. StIBI1 interacts with StVOZ1 and StVOZ2 in the cytoplasm, reducing the nuclear accumulation of StVOZ1 and promoting the nuclear accumulation of StVOZ2. Our findings indicate that StVOZ1 and StVOZ2 finely regulate potato resistance to late blight through distinct signaling pathways. In summary, our study provides insights into the interaction between the potato BABA receptor StIBI1 and the TFs StVOZ1 and StVOZ2, which affects StVOZ1 and StVOZ2 stability and nuclear accumulation to regulate late blight resistance during BABA-IR. This research advances our understanding of the primary mechanisms of BABA-IR in potato and contributes to a theoretical basis for the prevention and control of potato late blight using BABA-IR.

Effects of chitosan on plant growth under stress conditions: similarities with plant growth promoting bacteria

The agricultural use of synthetic pesticides, fertilizers, and growth regulators may represent a serious public health and environmental problem worldwide. All this has prompted the exploration of alternative chemical compounds, leading to exploring the potential of chitosan and PGPB in agricultural systems as a potential biotechnological solution to establish novel agricultural production practices that not only result in fewer adverse impacts on health and the environment but also improve the resilience and growth of the plants. In this work, an analysis of the impact of plant growth-promoting bacteria (PGPB) and chitosan on plant growth and protection has been conducted, emphasizing the crucial bioactivities of the resistance of the plants to both biotic and abiotic stressors. These include inducing phytohormone production, mobilization of insoluble soil nutrients, biological nitrogen fixation, ethylene level regulation, controlling soil phytopathogens, etc. Moreover, some relevant aspects of chitin and chitosan are discussed, including their chemical structures, sources, and how their physical properties are related to beneficial effects on agricultural applications and mechanisms of action. The effects of PGPB and chitosan on photosynthesis, germination, root development, and protection against plant diseases have been compared, emphasizing the intriguing similarities and synergistic effects observed in some of these aspects. Although currently there are limited studies focused on the combined application of PGPB and chitosan, it would be important to consider the similarities highlighted in this work, and those that may emerge in future studies or through well-designed investigations, because these could permit advancing towards a greater knowledge of these systems and to obtain better formulations by combining these bioproducts, especially for use in the new contexts of sustainable agriculture. Thus, it seems feasible to augur a promising near future for these combinations, considering the wide range of possibilities offered by chitinous biomaterials for the development of innovative formulations, as well as allowing different application methods. Likewise, the studies related to the PGPB effects on plant growth appear to be expanding due to ongoing research to test on plants the impacts of microorganisms derived from different environments, whether known or recently discovered, making it a very exciting field of research.

Application of Chitosan and Its Derivatives Against Plant Viruses

Chitosan is a natural biopolymer that is industrially produced from chitin via deacetylation. Due to its unique properties and a plethora of biological activities, chitosan has found application in diverse areas from biomedicine to agriculture and the food sector. Chitosan is regarded as a biosafe, biodegradable, and biocompatible compound that was demonstrated to stimulate plant growth and to induce a general plant defense response, enhancing plant resistance to various pathogens, including bacteria, fungi, nematodes, and viruses. Here, we focus on chitosan application as an antiviral agent for plant protection. We review both the pioneer studies and recent research that report the effect of plant treatment with chitosan and its derivatives on viral infection. Special attention is paid to aspects that affect the biological activity of chitosan: polymer length and, correspondingly, its molecular weight; concentration; deacetylation degree and charge; application protocol; and experimental set-up. Thus, we compare the reported effects of various forms and derivatives of chitosan as well as chitosan-based nanomaterials, focusing on the putative mechanisms underlying chitosan-induced plant resistance to plant viruses.

Carbohydrate elicitor-induced plant immunity: Advances and prospects

The perceived negative impacts of synthetic agrochemicals gave way to alternative, biological plant protection strategies. The deployment of induced resistance, comprising boosting the natural defense responses of plants, is one of those. Plants developed multi-component defense mechanisms to defend themselves against biotic and abiotic stresses. These are activated upon recognition of stress signatures via membrane-localized receptors. The induced immune responses enable plants to tolerate and limit the impact of stresses. A systemic cascade of signals enables plants to prime un-damaged tissues, which is crucial during secondary encounters with stress. Comparable stress tolerance mechanisms can be induced in plants by the application of carbohydrate elicitors such as chitin/chitosan, β-1,3-glucans, oligogalacturonides, cellodextrins, xyloglucans, alginates, ulvans, and carrageenans. Treating plants with carbohydrate-derived elicitors enable the plants to develop resistance appliances against diverse stresses. Some carbohydrates are also known to have been involved in promoting symbiotic signaling. Here, we review recent progresses on plant resistance elicitation effect of various carbohydrate elicitors and the molecular mechanisms of plant cell perception, cascade signals, and responses to cascaded cues. Besides, the molecular mechanisms used by plants to distinguish carbohydrate-induced immunity signals from symbiotic signals are discussed. The structure-activity relationships of the carbohydrate elicitors are also described. Furthermore, we forwarded future research outlooks that might increase the utilization of carbohydrate elicitors in agriculture in order to improve the efficacy of plant protection strategies.

Fighting for Survival at the Stomatal Gate

Stomata serve as the battleground between plants and plant pathogens. Plants can perceive pathogens, inducing closure of the stomatal pore, while pathogens can overcome this immune response with their phytotoxins and elicitors. In this review, we summarize new discoveries in stomata-pathogen interactions. Recent studies have shown that stomatal movement continues to occur in a close-open-close-open pattern during bacterium infection, bringing a new understanding of stomatal immunity. Furthermore, the canonical pattern-triggered immunity pathway and ion channel activities seem to be common to plant-pathogen interactions outside of the well-studied Arabidopsis-Pseudomonas pathosystem. These developments can be useful to aid in the goal of crop improvement. New technologies to study intact leaves and advances in available omics data sets provide new methods for understanding the fight at the stomatal gate. Future studies should aim to further investigate the defense-growth trade-off in relation to stomatal immunity, as little is known at this time.

Exploring the effects of red light night break on the defence mechanisms of tomato against fungal pathogen Botrytis cinerea

Plant infections caused by fungi lead to significant crop losses worldwide every year. This study aims to better understand the plant defence mechanisms regulated by red light, in particular, the effects of red light at night when most phytopathogens are highly infectious. Our results showed that superoxide production significantly increased immediately after red light exposure and, together with hydrogen peroxide levels, was highest at dawn after 30 min of nocturnal red-light treatment. In parallel, red-light-induced expression and increased the activities of several antioxidant enzymes. The nocturnal red light did not affect salicylic acid but increased jasmonic acid levels immediately after illumination, whereas abscisic acid levels increased 3 h after nocturnal red-light exposure at dawn. Based on the RNAseq data, red light immediately increased the transcription of several chloroplastic chlorophyll a-b binding protein and circadian rhythm-related genes, such as Constans 1, CONSTANS interacting protein 1 and zinc finger protein CONSTANS-LIKE 10. In addition, the levels of several transcription factors were also increased after red light exposure, such as the DOF zinc finger protein and a MYB transcription factor involved in the regulation of circadian rhythms and defence responses in tomato. In addition to identifying these key transcription factors in tomato, the application of red light at night for one week not only reactivated key antioxidant enzymes at the gene and enzyme activity level at dawn but also contributed to a more efficient and successful defence against Botrytis cinerea infection.

Natural variation in the pattern-triggered immunity response in plants: Investigations, implications and applications

The pattern-triggered immunity (PTI) response is triggered at the plant cell surface by the recognition of microbe-derived molecules known as microbe- or pathogen-associated molecular patterns or molecules derived from compromised host cells called damage-associated molecular patterns. Membrane-localized receptor proteins, known as pattern recognition receptors, are responsible for this recognition. Although much of the machinery of PTI is conserved, natural variation for the PTI response exists within and across species with respect to the components responsible for pattern recognition, activation of the response, and the strength of the response induced. This review describes what is known about this variation. We discuss how variation in the PTI response can be measured and how this knowledge might be utilized in the control of plant disease and in developing plant varieties with enhanced disease resistance.

The local and systemic accumulation of ethylene determines the rapid defence responses induced by flg22 in tomato (Solanum lycopersicum L.)

Plant defence responses induced by the bacterial elicitor flg22 are highly dependent on phytohormones, including gaseous ethylene (ET). While the regulatory role of ET in local defence responses to flg22 exposure has been demonstrated, its contribution to the induction of systemic responses is not clearly understood. For this consideration, we examined the effects of different ET modulators on the flg22-induced local and systemic defence progression. In our experiments, ET biosynthesis inhibitor aminoethoxyvinyl glycine (AVG) or ET receptor blocker silver thiosulphate (STS) were applied 1 h before flg22 treatments and 1 h later the rapid local and systemic responses were detected in the leaves of intact tomato plants (Solanum lycopersicum L.). Based on our results, AVG not only diminished the flg22-induced ET accumulation locally, but also in the younger leaves confirming the role of ET in the whole-plant expanding defence progression. This increase in ET emission was accompanied by increased local expression of SlACO1, which was reduced by AVG and STS. Local ET biosynthesis upon flg22 treatment was shown to positively regulate local and systemic superoxide (O2.-) and hydrogen peroxide (H2O2) production, which in turn could contribute to ET accumulation in younger leaves. Confirming the role of ET in flg22-induced rapid defence responses, application of AVG reduced local and systemic ET, O2.- and H2O2 production, whereas STS reduced it primarily in the younger leaves. Interestingly, in addition to flg22, AVG and STS induced stomatal closure alone at whole-plant level, however in the case of combined treatments together with flg22 both ET modulators reduced the rate of stomatal closure in the older- and younger leaves as well. These results demonstrate that both local and systemic ET production in sufficient amounts and active ET signalling are essential for the development of flg22-induced rapid local and systemic defence responses.

The Effect of Chitosan on Plant Physiology, Wound Response, and Fruit Quality of Tomato

In agriculture, chitosan has become popular as a metabolic enhancer; however, no deep information has been obtained yet regarding its mechanisms on vegetative tissues. This work was conducted to test the impact of chitosan applied at different plant growth stages on plant development, physiology, and response to wounding as well as fruit shape and composition. Five concentrations of chitosan were tested on tomato. The most effective chitosan doses that increased leaf number, leaf area, plant biomass, and stomatal conductance were 0.75 and 1 mg mL^-1. Chitosan (1 mg mL^-1) applied as foliar spray increased the levels of jasmonoyl-isoleucine and abscisic acid in wounded roots. The application of this dose at vegetative and flowering stages increased chlorophyll fluorescence (Fv/Fm) values, whereas application at the fruit maturation stage reduced the Fv/Fm values. This decline was positively correlated with fruit shape and negatively correlated with the pH and the content of soluble sugars, lycopene, total flavonoids, and nitrogen in fruits. Moreover, the levels of primary metabolites derived from glycolysis, such as inositol phosphate, lactic acid, and ascorbic acid, increased in response to treatment of plants with 1 mg mL^-1- chitosan. Thus, chitosan application affects various plant processes by influencing stomata aperture, cell division and expansion, fruit maturation, mineral assimilation, and defense responses.

The role of photosynthetic activity in the regulation of flg22-induced local and systemic defence reaction in tomato

Flagellin (flg22) induces rapid and long-lasting defence responses. It may also affect the photosynthetic activity depending on several internal and external factors, such as the phytohormone ethylene or the day/night time. Based on the results, flg22 treatment, neither in the light phase nor in the evening, caused any significant change in chlorophyll fluorescence induction parameters in the leaves of wild-type and ethylene-receptor mutant Never ripe tomato plants measured the next morning. However, flg22 in the light phase decreased the effective quantum yield and the photochemical quenching both locally and systemically in guard cells. In parallel, the production of reactive oxygen species and nitric oxide increased, which contributed to the stomatal closure and a decrease in CO2 assimilation the next day. A decrease in sugar content and elevated hexokinase activity measured after flg22 exposure can also contribute to local defence responses in intact tomato plants.

Light Deficiency Inhibits Growth by Affecting Photosynthesis Efficiency as well as JA and Ethylene Signaling in Endangered Plant Magnolia sinostellata

The endangered plant Magnolia sinostellata largely grows in the understory of forest and suffers light deficiency stress. It is generally recognized that the interaction between plant development and growth environment is intricate; however, the underlying molecular regulatory pathways by which light deficiency induced growth inhibition remain obscure. To understand the physiological and molecular mechanisms of plant response to shading caused light deficiency, we performed photosynthesis efficiency analysis and comparative transcriptome analysis in M. sinostellata leaves, which were subjected to shading treatments of different durations. Most of the parameters relevant to the photosynthesis systems were altered as the result of light deficiency treatment, which was also confirmed by the transcriptome analysis. Gene Ontology and KEGG pathway enrichment analyses illustrated that most of differential expression genes (DEGs) were enriched in photosynthesis-related pathways. Light deficiency may have accelerated leaf abscission by impacting the photosynthesis efficiency and hormone signaling. Further, shading could repress the expression of stress responsive transcription factors and R-genes, which confer disease resistance. This study provides valuable insight into light deficiency-induced molecular regulatory pathways in M. sinostellata and offers a theoretical basis for conservation and cultivation improvements of Magnolia and other endangered woody plants.