Bio-based resistance inducers for sustainable plant protection against pathogens

In Vitro and In Vivo Antifungal Activity of Clove (Eugenia caryophyllata) and Pepper (Piper nigrum L.) Essential Oils and Functional Extracts Against Fusarium oxysporum and Aspergillus niger in Tomato (Solanum lycopersicum L.)

In this study, hydrodistillation was used to obtain essential oils (EOs) from pepper (Piper nigrum L.) and clove (Eugenia caryophyllata) and co-hydrodistillation (addition of fatty acid ethyl esters as extraction co-solvents) was used to obtain functional extracts (FEs). Antifungal activity of EOs and FEs was evaluated by determination of minimum inhibitory concentration (MIC) against Fusarium oxysporum and Aspergillus niger. The results showed that pepper (Piper nigrum) and clove (Eugenia caryophyllata) essential oils and their functional extracts are effective in vitro at concentrations from 400 to 500 ppm after 10 days of culturing. The essential oils and functional extracts were used on tomato fruit samples at three different concentrations: 350, 400, and 450 ppm⁵. Clove essential oil reduced the growth of Aspergillus niger from 50% to 70% and Fusarium oxysporum to 40%. The functional extracts (FEs) of clove and pepper, mixed with ethyl decanoate (FEs-C₁₀), were the best combination for protecting the tomato fruit in vivo against both phytopathogenic fungi. Gas chromatography-mass spectrometry (GC-MS) was used to identify eugenol as the principal compound in clove oil and limonene, sabinene, and β-caryophyllene in pepper oil.

Chitosan-Based Agronanochemicals as a Sustainable Alternative in Crop Protection

The rise in the World's food demand in line with the increase of the global population has resulted in calls for more research on the production of sustainable food and sustainable agriculture. A natural biopolymer, chitosan, coupled with nanotechnology could offer a sustainable alternative to the use of conventional agrochemicals towards a safer agriculture industry. Here, we review the potential of chitosan-based agronanochemicals as a sustainable alternative in crop protection against pests, diseases as well as plant growth promoters. Such effort offers better alternatives: (1) the existing agricultural active ingredients can be encapsulated into chitosan nanocarriers for the formation of potent biocides against plant pathogens and pests; (2) the controlled release properties and high bioavailability of the nanoformulations help in minimizing the wastage and leaching of the agrochemicals' active ingredients; (3) the small size, in the nanometer regime, enhances the penetration on the plant cell wall and cuticle, which in turn increases the argochemical uptake; (4) the encapsulation of agrochemicals in chitosan nanocarriers shields the toxic effect of the free agrochemicals on the plant, cells and DNA, thus, minimizing the negative impacts of agrochemical active ingredients on human health and environmental wellness. In addition, this article also briefly reviews the mechanism of action of chitosan against pathogens and the elicitations of plant immunity and defense response activities of chitosan-treated plants.

JA-Ile-macrolactone 5b Induces Tea Plant (Camellia sinensis) Resistance to Both Herbivore Ectropis obliqua and Pathogen Colletotrichum camelliae

Jasmonates (JAs), the group of lipid-derived hormones, were found to control the defense responses in a myriad of plants. Meaningfully, the macrolactones of 12-hydroxy jasmonate isoleucine (12OH-JA-Ile) were reported to induce the defensive response of wild tobacco. However, little to nothing has been known about the elicitation effect of JA-Ile-macrolactones on woody plants to harmful organisms, let alone its underlying mechanisms. Here, we first optimized the synthetic routine using mild toxic reagent isobutyl chloroformate instead of ethyl chloroformate for conjugation, and we used acetonitrile (MeCN) instead of ethyl alcohol for the better dissolution of p-toluenesulfonic acid (p-TsOH) to gain JA-Ile-macrolactones. JA-Ile-macrolactone 5b-treated tea plants significantly inhibited the larvae weight gain of Ectropis obliqua larvae and the lesions caused by Colletotrichum camelliae. Furthermore, the expression level of CsOPR3 was significantly upregulated in 5b-treated leaves. Meanwhile, 5b reduced the accumulation of eriodictyol 7-O-glucuronide (EDG) in tea plants, which was confirmed to promote the growth rate of E. obliqua larvae by artificial diet assay. In conclusion, our study proved that the exogenous application of 5b could induce the tea plant resistance both to herbivore E. obliqua and pathogen C. camelliae, and EDG was identified as one of the secondary metabolites that could influence the growth rate of E. obliqua, but it did not directly influence the infection of C. camelliae in vitro. Further research should be carried out to clarify the mechanism through which 5b induces tea plant resistance to C. camelliae.

Cannabis Microbiome and the Role of Endophytes in Modulating the Production of Secondary Metabolites: An Overview

Plants, including cannabis (Cannabis sativa subsp. sativa), host distinct beneficial microbial communities on and inside their tissues and organs, including seeds. They contribute to plant growth, facilitating mineral nutrient uptake, inducing defence resistance against pathogens, and modulating the production of plant secondary metabolites. Understanding the microbial partnerships with cannabis has the potential to affect the agricultural practices by improving plant fitness and the yield of cannabinoids. Little is known about this beneficial cannabis-microbe partnership, and the complex relationship between the endogenous microbes associated with various tissues of the plant, and the role that cannabis may play in supporting or enhancing them. This review will consider cannabis microbiota studies and the effects of endophytes on the elicitation of secondary metabolite production in cannabis plants. The review aims to shed light on the importance of the cannabis microbiome and how cannabinoid compound concentrations can be stimulated through symbiotic and/or mutualistic relationships with endophytes.

Chitosan guar nanoparticle preparation and its in vitro antimicrobial activity towards phytopathogens of rice

The aim of the present study was to prepare chitosan guar nanoparticle (CGNP) with high antimicrobial activity to use as a bioprotectant against rice phytopathogens. Nanoparticles were prepared using sodium tripolyphosphate by the ionic gelation method. The physico-chemical properties of nanoparticles were characterized through DLS, FTIR, TEM, SEM, AFM and XRD. The application of CGNP to rice seeds stimulated seed germination and seedling growth. CGNP showed growth inhibition towards rice pathogens P. grisea and X. oryzae under in-vitro condition. Excised rice leaves treated with CGNP and challenged with P. grisea showed no blast disease symptom whereas control leaves showed very high blast disease symptom. The results of this study indicate that CGNP can be used as an antimicrobial agent to control blast, blight disease of rice.

Reynoutria sachalinensis extract elicits SA-dependent defense responses in courgette genotypes against powdery mildew caused by Podosphaera xanthii

Powdery mildew (PM) caused by Podosphaera xanthii is one of the most important courgette diseases with high yield losses and is currently controlled by fungicides and sulphur applications in conventional and organic production. Plant derived elicitors/inducers of resistance are natural compounds that induce resistance to pathogen attack and promote a faster and/or more robust activation of plant defense responses. Giant knotweed (Reynoutria sachalinensis, RS) extract is a known elicitor of plant defenses but its mode of action remains elusive. The aim of this study was to investigate the mechanisms of foliar RS applications and how these affect PM severity and crop performance when used alone or in combination with genetic resistance. RS foliar treatments significantly reduced conidial germination and PM severity on both an intermediate resistance (IR) and a susceptible (S) genotype. RS application triggered plant defense responses, which induced the formation of callose papillae, hydrogen peroxide accumulation and the Salicylic acid (SA) - dependent pathway. Increased SA production was detected along with increased p-coumaric and caffeic acid concentrations. These findings clearly indicate that RS elicits plant defenses notably as a consequence of SA pathway induction.

The ptsG Gene Encoding the Major Glucose Transporter of Bacillus cereus C1L Participates in Root Colonization and Beneficial Metabolite Production to Induce Plant Systemic Disease Resistance

Rhizosphere interactions between microorganisms and plants have great influence on plant health. Bacillus cereus C1L, an induced systemic resistance (ISR)-eliciting rhizobacterium from Lilium formosanum, can protect monocot and dicot plants from disease challenges. To identify the ISR-involved bacterial genes, the systemic protection effect of transposon-tagged mutants of B. cereus C1L against southern corn leaf blight (SCLB) was surveyed, and a mutant of the ptsG gene encoding glucose-specific permease of the phosphotransferase system was severely impaired in the abilities of disease suppression and root colonization. The ptsG mutant lost the preferential utilization of glucose and showed reduction of glucose-assisted growth in minimal medium. A promoter-based reporter assay revealed that ptsG expression could be activated by certain sugar constituents of maize root exudates, among which B. cereus C1L exhibited the highest chemotactic response toward glucose, whereas neither of them could attract the ptsG mutant. Additionally, ptsG deficiency almost completely abolished glucose uptake of B. cereus C1L. Metabolite analysis indicated that the lack of ptsG undermined glucose-induced accumulation of acetoin and 2,3-butanediol in B. cereus C1L, both eliciting maize ISR against SCLB. Pretreatments with B. cereus C1L, ptsG mutant, acetoin, and 2,3-butanediol enhanced defense-related reactive oxygen species accumulation and callose deposition at different levels that were positively correlated to their ISR-eliciting activities. Thus, glucose uptake-mediating ptsG participates in ISR elicitation by endowing B. cereus C1L with the full capacities for root colonization and beneficial glucose metabolite production, providing a clue regarding how ISR-mediating rhizobacteria create a mutually beneficial relationship with various plant species.

Biological protection of spring wheat from root rot in the forest-steppe zone of Eastern Siberia

We present the results of the trial of the biological drug BisolbiSan (Bacillus subtillis strain H-13, isolated by the All-Russian Research Institute of Agricultural Microbiology) for treatment of spring wheat seeds in comparison with the widely popular chemical fungicides Maxim and Maxim Plus in the forest-steppe zone of Eastern Siberia in 2016–2018. BisolbiSan contributed to a decrease in total seed contamination by 2.4 times compared to control, which was practically at the level of the chemical fungicide Maxim. Maxim and Maxim Plus oppressed the growth of the sprout and the main germ line, while BisolbiSan stimulated the growth and development of the root system, and did not inhibit the growth of the sprout. The prevalence of root rot in the variant with BisolbiSan was lower compared to control by 54 %, effectiveness of which was not significantly inferior to that of chemical protectants. In comparison with control variant, BisolbiSan increased vitreous content of grain by 16.9 %, the content of crude gluten by 3.9 %, contributed to obtaining a statistically reliable increase in the yield of 0.38 tons per hectare, which did not differ significantly from the increase in the variant with chemical protectants. In our experiment, the payback of 1 ruble of costs when treating seeds with BisolbiSan was 1.7, which is 0.5 and 0.2 rubles higher compared to Maxim and Maxim Plus, respectively. The profitability of the yield increase using BisolbiSan was 70.9 %, which is 54.5 % and 20.6 % more than when using Maxim and Maxim Plus, respectively.

Mecanismos de acción de <i>Bacillus</i> spp. (Bacillaceae) contra microorganismos fitopatógenos durante su interacción con plantas

Algunos Bacillus spp. promotores de crecimiento vegetal son microorganismos reconocidos como agentes de control biológico que forman una estructura de resistencia denominada endospora, que les permite sobrevivir en ambientes hostiles y estar en casi todos los agroecosistemas. Estos microorganismos han sido reportados como alternativa al uso de agroquímicos. Sus mecanismos de acción se pueden dividir en: producción de compuestos antimicrobianos, como son péptidos de síntesis no ribosomal (NRPs) y policétidos (PKs); producción de hormonas, capacidad de colonización, formación de biopelículas y competencia por espacio y nutrientes; síntesis de enzimas líticas como quitinasas, glucanasas, protesasas y acil homoserin lactonasas (AHSL); producción de compuestos orgánicos volátiles (VOCs); e inducción de resistencia sistémica (ISR). Estos mecanismos han sido reportados en la literatura en diversos estudios, principalmente llevados a cabo a nivel in vitro. Sin embargo, son pocos los estudios que contemplan la interacción dentro del sistema tritrófico: planta – microorganismos patógenos – Bacillus sp. (agente biocontrolador), a nivel in vivo. Es importante destacar que la actividad biocontroladora de los Bacillus es diferente cuando se estudia bajo condiciones de laboratorio, las cuales están sesgadas para lograr la máxima expresión de los mecanismos de acción. Por otra parte, a nivel in vivo, la interacción con la planta y el patógeno juegan un papel fundamental en la expresión de dichos mecanismos de acción, siendo esta más cercana a la situación real de campo. Esta revisión se centra en los mecanismos de acción de los Bacillus promotores de crecimiento vegetal, expresados bajo la interacción con la planta y el patógeno.

Synthesis and application of chitosan-copper nanoparticles on damping off causing plant pathogenic fungi

Damping-off disease in seeds and young seedlings in agricultural crops is a major fungal disease that limits the agriculture production. Frequent use of synthetic fungicides against damping-off diseases is known to hamper the environmental balance. Thus, an alternative approach needs to be explored for the management of such economically important fungal diseases. In the present study, simple, economically feasible chitosan-coupled copper nanoparticles (Ch-CuNPs) were synthesized and demonstrated antifungal activity against damping-off disease causing phytopathogens, Rhizoctonia solani and Pythium aphanidermatum. Physico-chemical studies confirmed the size, shape, surface charge, element confirmation and mono-dispersed nature of Ch-CuNPs. In vitro efficacy studies revealed up to 98% mycelial growth inhibition at 0.1% Ch-CuNPs. An extracellular conductivity study of the mycelium showed cellular content leakage within 12 h of treatment. Further, plant toxicity study against chili, cowpea and tomato plants; showed that ≤0.2% NPs were safe under greenhouse conditions. NPs also exhibited growth-promoting activity with chili seeds, by overcoming the limited germination rate of susceptible seeds. Overall, the present study emphasizes the benefits of synthesized Ch-CuNPs on agricultural crops as fungicide and growth-promoter, as well as a safe alternative to pesticides in order to avoid hazardous effect on the environment.

Carbohydrate polymers exhibit great potential as effective elicitors in organic agriculture: A review

Some carbohydrate polymers, usually oligosaccharides or polysaccharides, have great potential as an elicitor of plant defense. However, due to the complexity and diversity of poly- and oligosaccharide structure, the molecular mechanisms and structure-activity relationships of carbohydrate elicitors are still not well understood, which hinders the application of carbohydrate elicitors in agriculture. This review introduces the mechanisms of carbohydrate elicitor perception and signaling in plants. The structure and activity relationships of main poly- and oligosaccharides studied for the control of plant diseases are discussed and summarized. Additionally, the effects of carbohydrate elicitors on the secondary metabolite production are also summarized.

A Biostimulant Preparation of Brown Seaweed Ascophyllum nodosum Suppresses Powdery Mildew of Strawberry

Strawberry, an important fruit crop, is susceptible to a large number of pathogens that reduce fruit quality and productivity. In this study, the effect of a biostimulant prepared from Ascophyllum nodosum extract (ANE) (0.1%, 0.2%, and 0.3%) was evaluated on powdery mildew progression under greenhouse and field conditions. In the greenhouse, application of 0.2% ANE showed maximum reduction in powdery mildew progression as compared to the control. Forty-eight hour post-inoculation, foliar spray of 0.2% ANE reduced spore germination by 75%. Strawberry leaves sprayed with ANE showed higher total phenolic and flavonoid content in response to powdery mildew infection. Furthermore, application of ANE elicited defense response in strawberry plants by induction of defense-related enzymes, such as phenylalanine ammonia lyase, polyphenol oxidase, and peroxidase activity. In field conditions, foliar spray of 0.2% ANE showed a reduction of 37.2% of natural incidence of powdery mildew infection as compared to the control. ANE sprayed plant also reduces the severity of powdery mildew infection under natural conditions. These results indicate that application of ANE induces the strawberry plant's active defense against powdery mildew infection by induction of secondary metabolism and regulating the activities of defense-related enzymes.

Oregano essential oil vapour prevents Plasmopara viticola infection in grapevine (Vitis Vinifera) and primes plant immunity mechanisms

The reduction of synthetic fungicides in agriculture is necessary to guarantee a sustainable production that protects the environment and consumers' health. Downy mildew caused by the oomycete Plasmopara viticola is the major pathogen in viticulture worldwide and responsible for up to 60% of pesticide treatments. Alternatives to reduce fungicides are thus utterly needed to ensure sustainable vineyard-ecosystems, consumer health and public acceptance. Essential oils (EOs) are amongst the most promising natural plant protection alternatives and have shown their antibacterial, antiviral and antifungal properties on several agricultural crops. However, the efficiency of EOs highly depends on timing, application method and the molecular interactions between the host, the pathogen and EO. Despite proven EO efficiency, the underlying processes are still not understood and remain a black box. The objectives of the present study were: a) to evaluate whether a continuous fumigation of a particular EO can control downy mildew in order to circumvent the drawbacks of direct application, b) to decipher molecular mechanisms that could be triggered in the host and the pathogen by EO application and c) to try to differentiate whether essential oils directly repress the oomycete or act as plant resistance primers. To achieve this a custom-made climatic chamber was constructed that enabled a continuous fumigation of potted vines with different EOs during long-term experiments. The grapevine (Vitis vinifera) cv Chasselas was chosen in reason of its high susceptibility to Plasmopara viticola. Grapevine cuttings were infected with P. viticola and subsequently exposed to continuous fumigation of different EOs at different concentrations, during 2 application time spans (24 hours and 10 days). Experiments were stopped when infection symptoms were clearly observed on the leaves of the control plants. Plant physiology (photosynthesis and growth rate parameters) were recorded and leaves were sampled at different time points for subsequent RNA extraction and transcriptomics analysis. Strikingly, the Oregano vulgare EO vapour treatment during 24h post-infection proved to be sufficient to reduce downy mildew development by 95%. Total RNA was extracted from leaves of 24h and 10d treatments and used for whole transcriptome shotgun sequencing (RNA-seq). Sequenced reads were then mapped onto the V. vinifera and P. viticola genomes. Less than 1% of reads could be mapped onto the P. viticola genome from treated samples, whereas up to 30% reads from the controls mapped onto the P. viticola genome, thereby confirming the visual observation of P. viticola absence in the treated plants. On average, 80% of reads could be mapped onto the V. vinifera genome for differential expression analysis, which yielded 4800 modulated genes. Transcriptomic data clearly showed that the treatment triggered the plant's innate immune system with genes involved in salicylic, jasmonic acid and ethylene synthesis and signaling, activating Pathogenesis-Related-proteins as well as phytoalexin synthesis. These results elucidate EO-host-pathogen interactions for the first time and indicate that the antifungal efficiency of EO is mainly due to the triggering of resistance pathways inside the host plants. This is of major importance for the production and research on biopesticides, plant stimulation products and for resistance-breeding strategies.

Nodulation Induces Systemic Resistance of Medicago truncatula and Pisum sativum Against Erysiphe pisi and Primes for Powdery Mildew-Triggered Salicylic Acid Accumulation

Plants encounter beneficial and detrimental microorganisms both above- and belowground and the health status of the plant depends on the composition of this pan-microbiome. Beneficial microorganisms contribute to plant nutrition or systemically or locally protect plants against pathogens, thus facilitating adaptation to a variety of environments. Induced systemic resistance, caused by root-associated microbes, manifests as aboveground resistance against necrotrophic pathogens and is mediated by jasmonic acid/ethylene-dependent signaling. By contrast, systemic acquired resistance relies on salicylic acid (SA) signaling and confers resistance against secondary infection by (hemi)biotrophic pathogens. To investigate whether symbiotic rhizobia that are ubiquitously found in natural ecosystems are able to modulate resistance against biotrophs, we tested the impact of preestablished nodulation of Medicago truncatula and pea (Pisum sativum) plants against infection by the powdery mildew fungus Erysiphe pisi. We found that root symbiosis interfered with fungal penetration of M. truncatula and reduced asexual spore formation on pea leaves independently of symbiotic nitrogen fixation. Improved resistance of nodulated plants correlated with elevated levels of free SA and SA-dependent marker gene expression upon powdery mildew infection. Our results suggest that nodulation primes the plants systemically for E. pisi-triggered SA accumulation and defense gene expression, resulting in increased resistance.

Use of Ganoderma Lucidum polysaccharide to control cotton fusarium wilt, and the mechanism involved

Induced resistance is an effective measure for controlling plant diseases by utilizing the natural defense of the host and meets the strategic needs of pesticide application and safety for agricultural products worldwide. Ganoderma lucidum polysaccharide (GLP), which is the main active molecule of G. lucidum, has been widely used in functional food and clinical medicine. However, there are few reports of the use of GLP for the prevention and control of plant diseases. The purpose of this study is to explore the effect of GLP and its mechanism of inducing plant resistance. In this study, we found that GLP spray and irrigation root treatments can promote growth in cotton. After soaking in GLP, theseedling height and cotton fusarium wilt resistance both increased to some extent, effects that were dose dependent. After treatment of cotton with GLP, the activities of peroxidase (POD), superoxide dismutase (SOD) and polyphenol oxidase (PPO) in leaves increased significantly, whereas the content of malondialdehyde (MDA) decreased. In addition, QRT-PCR results showed significantly increased relative expression of genes related to the jasmonic acid pathway in cotton. Therefore, we speculate that GLP can induce plant resistance by stimulating the jasmonate pathway.

Dual Mode of the Saponin Aescin in Plant Protection: Antifungal Agent and Plant Defense Elicitor

Being natural plant antimicrobials, saponins have potential for use as biopesticides. Nevertheless, their activity in plant-pathogen interaction is poorly understood. We performed a comparative study of saponins' antifungal activities on important crop pathogens based on their effective dose (EC₅₀) values. Among those saponins tested, aescin showed itself to be the strongest antifungal agent. The antifungal effect of aescin could be reversed by ergosterol, thus suggesting that aescin interferes with fungal sterols. We tested the effect of aescin on plant-pathogen interaction in two different pathosystems: Brassica napus versus (fungus) Leptosphaeria maculans and Arabidopsis thaliana versus (bacterium) Pseudomonas syringae pv tomato DC3000 (Pst DC3000). We analyzed resistance assays, defense gene transcription, phytohormonal production, and reactive oxygen species production. Aescin activated B. napus defense through induction of the salicylic acid pathway and oxidative burst. This defense response led finally to highly efficient plant protection against L. maculans that was comparable to the effect of fungicides. Aescin also inhibited colonization of A. thaliana by Pst DC3000, the effect being based on active elicitation of salicylic acid (SA)-dependent immune mechanisms and without any direct antibacterial effect detected. Therefore, this study brings the first report on the ability of saponins to trigger plant immune responses. Taken together, aescin in addition to its antifungal properties activates plant immunity in two different plant species and provides SA-dependent resistance against both fungal and bacterial pathogens.

Recent Advances in Synthetic Chemical Inducers of Plant Immunity

Different from the conventional biocidal agrochemicals, synthetic chemical inducers of plant immunity activate, bolster, or prime plant defense machineries rather than directly acting on the pathogens. Advances in combinatorial synthesis and high-throughput screening methods have led to the discovery of various synthetic plant immune activators as well as priming agents. The availability of their structures and recent progress in the mechanistic understanding of plant immune responses have opened up the possibility of identifying new or more potent chemical inducers through rational design. In this review, we first summarize the chemical inducers identified through large-scale screening and then discuss the emerging trends in the identification and development of novel plant immune inducers including natural elicitor based chemical derivation, bifunctional combination, and computer-aided design.

Fungal Endophytic Communities of Two Wild Rosa Varieties With Different Powdery Mildew Susceptibilities

Powdery mildew (PM) is one of the most devastating and wide spread fungal diseases of rose, which seriously decrease its productivity and commercial value. In the present study, the endophytic fungal communities of two wild Rosa varieties (Rosa multiflora Thunb and R. multiflora var. carnea Redouté and Thory) with different PM susceptibilities were studied through Illumina MiSeq sequencer. A total of 14,000,424 raw reads were obtained from 60 samples, and 6,862,953 tags were produced after merging paired-end reads. 4462 distinct OTUs were generated at a 97% similarity level. It was found that only 34.2% of OTUs shared between two plant varieties. All of the OTUs were assigned into four fungal phyla, 17 classes, 43 orders, 86 families, 157 genera, and 208 species. Members of Ascomycota were found to be the most common fungal endophytes (EF) among all plant samples (93.7% relative abundance), followed by Basidiomycota (4.7% relative abundance), while Zygomycota and Glomeromycota were found to be rare and incidental. At each developmental stage of plants, the diversity and community structure of EF between two Rosa varieties showed significant differences. Both PCoA plots and PERMANOVA analyses indicated that developmental stage was the major factor contributing to the difference between the Rosa varieties (R² = 0.348, p < 0.001). In addition, plant varieties and tissues were also important factors contributing to the difference (R² = 0.031, p < 0.05; R² = 0.029, p < 0.05). Moreover, Neofusicoccum, Rhodosporidium, and Podosphaera, etc., were found to be significantly different between two Rosa varieties, and some of the endophytes may play a role in PM resistance. These finding are encouraging to testify the potential use of these fungi in the biocontrol of PM in future studies.

Rhamnolipids From Pseudomonas aeruginosa Are Elicitors Triggering Brassica napus Protection Against Botrytis cinerea Without Physiological Disorders

Rhamnolipids (RLs) are amphiphilic molecules naturally produced by some bacteria with a large range of biological activities. Although some studies report their potential interest in plant protection, evaluation of their effects and efficiency on annual crops of worldwide agronomic interest is lacking. The main objective of this work was to investigate their elicitor and protective activities on rapeseed crop species while evaluating their physiological effects. Here we report that RLs from Pseudomonas aeruginosa secretome trigger an effective protection of Brassicanapus foliar tissues toward the fungus Botrytis cinerea involving the combination of plant defense activation and direct antimicrobial properties. We demonstrated their ability to activate canonical B.napus defense responses including reactive oxygen species production, expression of defense genes, along with callose deposits and stomatal closure as efficient physical protections. In addition, microscopic cell death observations and electrolyte leakage measurements indicated that RLs trigger a hypersensitive response-like defense in this plant. We also showed that foliar spray applications of RLs do not induce deleterious physiological consequences on plant growth or chlorophyll content and that RL protective properties are efficient on several grown cultivars of rapeseed. To our knowledge, this is the first report of RLs as an elicitor that suppresses fungal disease on tissues of an annual crop species under greenhouse conditions. Our results highlight the dual mode of action of these molecules exhibiting plant protection activation and antifungal activities and demonstrate their potential for crop cultures as environmental-friendly biocontrol solution.

Disease Resistance Mechanisms in Plants

Plants have developed a complex defense system against diverse pests and pathogens. Once pathogens overcome mechanical barriers to infection, plant receptors initiate signaling pathways driving the expression of defense response genes. Plant immune systems rely on their ability to recognize enemy molecules, carry out signal transduction, and respond defensively through pathways involving many genes and their products. Pathogens actively attempt to evade and interfere with response pathways, selecting for a decentralized, multicomponent immune system. Recent advances in molecular techniques have greatly expanded our understanding of plant immunity, largely driven by potential application to agricultural systems. Here, we review the major plant immune system components, state of the art knowledge, and future direction of research on plant⁻pathogen interactions. In our review, we will discuss how the decentralization of plant immune systems have provided both increased evolutionary opportunity for pathogen resistance, as well as additional mechanisms for pathogen inhibition of such defense responses. We conclude that the rapid advances in bioinformatics and molecular biology are driving an explosion of information that will advance agricultural production and illustrate how complex molecular interactions evolve.

CfPDIP1, a novel secreted protein of Colletotrichum falcatum, elicits defense responses in sugarcane and triggers hypersensitive response in tobacco

Colletotrichum falcatum, a hemibiotrophic fungal pathogen, causes one of the major devastating diseases of sugarcane-red rot. C. falcatum secretes a plethora of molecular signatures that might play a crucial role during its interaction with sugarcane. Here, we report the purification and characterization of a novel secreted protein of C. falcatum that elicits defense responses in sugarcane and triggers hypersensitive response (HR) in tobacco. The novel protein purified from the culture filtrate of C. falcatum was identified by MALDI TOF/TOF MS and designated as C. falcatum plant defense-inducing protein 1 (CfPDIP1). Temporal transcriptional profiling showed that the level of CfPDIP1 expression was greater in incompatible interaction than the compatible interaction until 120 h post-inoculation (hpi). EffectorP, an in silico tool, has predicted CfPDIP1 as a potential effector. Functional characterization of full length and two other domain deletional variants (CfPDIP1ΔN1-21 and CfPDIP1ΔN1-45) of recombinant CfPDIP1 proteins has indicated that CfPDIP1ΔN1-21 variant elicited rapid alkalinization and induced a relatively higher production of hydrogen peroxide (H2O2) in sugarcane suspension culture. However, in Nicotiana tabacum, all the three forms of recombinant CfPDIP1 proteins triggered HR along with the induction of H2O2 production and callose deposition. Further characterization using detached leaf bioassay in sugarcane revealed that foliar priming with CfPDIP1∆1-21 has suppressed the extent of lesion development, even though the co-infiltration of CfPDIP1∆1-21 with C. falcatum on unprimed leaves increased the extent of lesion development than control. Besides, the foliar priming has induced systemic expression of major defense-related genes with the concomitant reduction of pathogen biomass and thereby suppression of red rot severity in sugarcane. Comprehensively, the results have suggested that the novel protein, CfPDIP1, has the potential to trigger a multitude of defense responses in sugarcane and tobacco upon priming and might play a potential role during plant-pathogen interactions.

Application of Copper-Chitosan Nanoparticles Stimulate Growth and Induce Resistance in Finger Millet (Eleusine coracana Gaertn.) Plants against Blast Disease

Copper-chitosan nanoparticle (CuChNp) was synthesized and used to study its effect on finger millet plant as a model plant system. Our objective was to explore the efficacy of CuChNp application to control blast disease of finger millet. CuChNp was applied to finger millet either as a foliar spray or as a combined application (involving seed coat and foliar spray). Both the application methods enhanced growth profile of finger millet plants and increased yield. The increased yield was nearly 89% in combined application method. Treated finger millet plants challenged with Pyricularia grisea showed suppression of blast disease development when compared to control. Nearly 75% protection was observed in the combined application of CuChNp to finger millet plants. In CuChNp treated finger millet plants, a significant increase in defense enzymes was observed, which was detected both qualitatively and quantitatively. The suppression of blast disease correlates well with increased defense enzymes in CuChNp treated finger millet plants.

Ethyl Gallate Displays Elicitor Activities in Tobacco Plants

Alkyl gallates showed elicitor activities on tobacco in both whole plants and cell suspensions. Methyl gallate (MG), ethyl gallate (EG), and propyl gallate (PG) infiltration into tobacco leaves induced hypersensitive reaction-like lesions and topical production of autofluorescent compounds revealed under UV light. When sprayed on tobacco plants at 5 mM, EG promoted upregulation of defense-related genes such as the antimicrobial PR1, β-1,3-glucanase PR2, Chitinase PR3, and osmotin PR5 target genes. Tobacco BY-2 cells challenged with EG underwent cell death in 48 h, which was significantly reduced in the presence of the protease inhibitor aprotinin. The three alkyl gallates all caused alkalinization of the BY-2 extracellular medium, whereas gallic acid did not trigger any pH variation. Using EGTA or LaCl3, we showed that Ca2+ mobilization occurred in BY-2 cells elicited with EG. Overall, our findings are the first evidence of alkyl gallate elicitor properties with early perception events on the plasma membrane, potential hypersensitive reactions, and PR-related downstream defense responses in tobacco.

Comparative secretome analysis of Colletotrichum falcatum identifies a cerato-platanin protein (EPL1) as a potential pathogen-associated molecular pattern (PAMP) inducing systemic resistance in sugarcane

Colletotrichum falcatum, an intriguing hemibiotrophic fungal pathogen causes red rot, a devastating disease of sugarcane. Repeated in vitro subculturing of C. falcatum under dark condition alters morphology and reduces virulence of the culture. Hitherto, no information is available on this phenomenon at molecular level. In this study, the in vitro secretome of C. falcatum cultured under light and dark conditions was analyzed using 2-DE coupled with MALDI TOF/TOF MS. Comparative analysis identified nine differentially abundant proteins. Among them, seven proteins were less abundant in the dark-cultured C. falcatum, wherein only two protein species of a cerato-platanin protein called EPL1 (eliciting plant response-like protein) were found to be highly abundant. Transcriptional expression of candidate high abundant proteins was profiled during host-pathogen interaction using qRT-PCR. Comprehensively, this comparative secretome analysis identified five putative effectors, two pathogenicity-related proteins and one pathogen-associated molecular pattern (PAMP) of C. falcatum. Functional characterization of three distinct domains of the PAMP (EPL1) showed that the major cerato-platanin domain (EPL1∆N1-92) is exclusively essential for inducing defense and hypersensitive response (HR) in sugarcane and tobacco, respectively. Further, priming with EPL1∆N1-92 protein induced systemic resistance and significantly suppressed the red rot severity in sugarcane.

BIOLOGICAL SIGNIFICANCE

Being the first secretomic investigation of C. falcatum, this study has identified five potential effectors, two pathogenicity-related proteins and a PAMP. Although many reports have highlighted the influence of light on pathogenicity, this study has established a direct link between light and expression of effectors, for the first time. This study has presented the influence of a novel N-terminal domain of EPL1 in physical and biological properties and established the functional role of major cerato-platanin domain of EPL1 as a potential elicitor inducing systemic resistance in sugarcane. Comprehensively, the study has identified proteins that putatively contribute to virulence of C. falcatum and for the first time, demonstrated the potential role of EPL1 in inducing PAMP-triggered immunity (PTI) in sugarcane.

Sargassum muticum and Jania rubens regulate amino acid metabolism to improve growth and alleviate salinity in chickpea

The present study evaluates the potential of Sar gassum muticum (Sar) and Jan ia rubens (Jan) seaweeds for enhancing growth and mitigating soil-salinity in chickpea (Cicer arietinum L.). Under control conditions, Sar and Jan extracts improved chickpea growth which was attributed to their potential for increasing photosynthetic pigments, K⁺ and amino acids, particularly proline, in comparison with water-sprayed control. Upon stress imposition, chickpea growth was reduced in NaCl concentration-dependent manner, and principal component analysis (PCA) revealed Na⁺ accumulation and oxidative damage as major determinants of sensitivity at high salinity. Furthermore, amino acid quantification indicated activation/deactivation of overall metabolism in roots/shoots, as an adaptive strategy, for maintaining plant growth under salt stress. Sar and Jan extract supplementations provided stress amelioration, and PCA confirmed that improved growth parameters at high salinity were associated with enhanced activities of superoxide dismutase and peroxidase. Besides, four key amino acids, including serine, threonine, proline and aspartic acids, were identified from roots which maximally contribute to Sar- and Jan-mediated stress amelioration. Sar showed higher effectiveness than Jan under both control and salt stress conditions. Our findings highlight "bio-stimulant" properties of two seaweeds and provide mechanistic insight into their salt-ameliorating action which is relevant for both basic and applied research.

Sargassum muticum and Jania rubens regulate amino acid metabolism to improve growth and alleviate salinity in chickpea

The present study evaluates the potential of Sargassum muticum (Sar) and Jania rubens (Jan) seaweeds for enhancing growth and mitigating soil-salinity in chickpea (Cicer arietinum L.). Under control conditions, Sar and Jan extracts improved chickpea growth which was attributed to their potential for increasing photosynthetic pigments, K⁺ and amino acids, particularly proline, in comparison with water-sprayed control. Upon stress imposition, chickpea growth was reduced in NaCl concentration-dependent manner, and principal component analysis (PCA) revealed Na⁺ accumulation and oxidative damage as major determinants of sensitivity at high salinity. Furthermore, amino acid quantification indicated activation/deactivation of overall metabolism in roots/shoots, as an adaptive strategy, for maintaining plant growth under salt stress. Sar and Jan extract supplementations provided stress amelioration, and PCA confirmed that improved growth parameters at high salinity were associated with enhanced activities of superoxide dismutase and peroxidase. Besides, four key amino acids, including serine, threonine, proline and aspartic acids, were identified from roots which maximally contribute to Sar- and Jan-mediated stress amelioration. Sar showed higher effectiveness than Jan under both control and salt stress conditions. Our findings highlight “bio-stimulant” properties of two seaweeds and provide mechanistic insight into their salt-ameliorating action which is relevant for both basic and applied research.

Plant growth regulator-mediated anti-herbivore responses of cabbage (Brassica oleracea) against cabbage looper Trichoplusia ni Hübner (Lepidoptera: Noctuidae)

Plant elicitors can be biological or chemical-derived stimulators of jasmonic acid (JA) or salicylic acid (SA) pathways shown to prime the defenses in many crops. Examples of chemical elicitors of the JA and SA pathways include methyl-jasmonate and 1,2,3-benzothiadiazole-7-carbothioate (BTH or the commercial plant activator Actigard 50WG, respectively). The use of specific elicitors has been observed to affect the normal interaction between JA and SA pathways causing one to be upregulated and the other to be suppressed, often, but not always, at the expense of the plant's herbivore or pathogen defenses. The objective of this study was to determine whether insects feeding on Brassica crops might be negatively affected by SA inducible defenses combined with an inhibitor of detoxification and anti-oxidant enzymes that regulate the insect response to the plant's defenses. The relative growth rate of cabbage looper Trichoplusia ni Hübner (Lepidoptera: Noctuidae) fed induced cabbage Brassica oleraceae leaves with the inhibitor, quercetin, was significantly less than those fed control cabbage with and without the inhibitor. The reduced growth was related to the reduction of glutathione S-transferases (GSTs) by the combination of quercetin and increased levels of indole glucosinolates in the cabbage treated with BTH at 2.6× the recommended application rate. These findings may offer a novel combination of elicitor and synergist that can provide protection from plant disease and herbivores in cabbage and other Brassica crops.

Independent Preharvest Applications of Methyl Jasmonate and Chitosan Elicit Differential Upregulation of Defense-Related Genes with Reduced Incidence of Gray Mold Decay during Postharvest Storage of Fragaria chiloensis Fruit

The Chilean strawberry (Fragaria chiloensis) fruit has interesting organoleptic properties, but its postharvest life is affected by gray mold decay caused by Botrytis cinerea. The effect of preharvest applications of methyl jasmonate (MeJA) or chitosan on the molecular defense-related responses and protection against gray mold decay were investigated in Chilean strawberry fruit during postharvest storage. Specifically, we inoculated harvested fruit with B. cinerea spores and studied the expression of genes encoding for the pathogenesis-related (PR) proteins β-1,3-glucanases (FcBG2-1, FcBG2-2 and FcBG2-3) and chitinases (FcCHI2-2 and FcCHI3-1), and for polygalacturonase inhibiting proteins (FcPGIP1 and FcPGIP2) at 0, 2, 24, 48, and 72 h post inoculation (hpi). Remarkably, MeJA- and chitosan-treated fruit exhibited a lower incidence of B. cinerea infection than the control-treated at 48 and 72 hpi. At the molecular level, both are efficient elicitors for priming in F. chiloensis fruit since we observed an upregulation of the FcBG2-1, FcBG2-3, FcPGIP1, and FcPGIP2 at 0 hpi. Moreover, a chitosan-mediated upregulation of FcPGIPs at early times post inoculation (2-24 hpi) and MeJA upregulated FcBGs (24-72 hpi) and FcPGIP1 at later times could contribute to reduce B. cinerea incidence by differential upregulation of defense genes. We concluded that preharvest applications of MeJA or chitosan had a long-lasting effect on the reduction of B. cinerea incidence during postharvest as well as an enhancer effect on the induction of PR and PGIP gene expression.

Inflammatory Effects of the Plant Protection Product Stifenia (FEN560) on Vertebrates

Plant defense stimulators (PDSs) rely on the activation of plant innate immunity in order to protect crops against various pests. These molecules are thought to be a safer alternative to classical plant protection products. Given that innate immune systems share common features in plants and vertebrates, PDS can potentially cross-react with innate immunity of non-target organisms. To test this hypothesis, we studied effects of the commercial PDS Stifenia (FEN560), which is composed of crushed fenugreek seeds. We tested various concentrations of Stifenia (0.03–1 mg mL⁻¹) on human peripheral blood mononuclear cells and checked, 20 h later, cell metabolic activity (MA) using XTT assay, cell death by flow cytometry analysis, and IL-1β inflammatory cytokine released in the culture medium using ELISA. Stifenia induced a general decrease of the cell MA, which was concomitant with a dose-dependent release of IL-1β. Our results highlight the activation of human immune cells. The inflammatory effect of Stifenia was partially inhibited by pan-caspase inhibitor. Accordingly, Stifenia induced the release of p20 caspase-1 fragment into the culture medium suggesting the involvement of the NLRP3 inflammasome. Furthermore, we observed that Stifenia can induce cell death. We also tested the effect of Stifenia on Zebrafish larvae. After 24 h of exposure, Stifenia induced a dose-dependent IL-1β and TNFα gene expression. The human-cell-based approach developed in this work revealed a high sensitivity concerning inflammatory properties of a plant protection product. These tests could be routinely used to screen the potential adverse effects of this type of compounds. Finally, our results suggest a potential danger of using extensively certain PDS for crop protection.

Sulfated lentinan induced mitochondrial dysfunction leads to programmed cell death of tobacco BY-2 cells

Sulphated lentinan (sLTN) is known to act as a resistance inducer by causing programmed cell death (PCD) in tobacco suspension cells. However, the underlying mechanism of this effect is largely unknown. Using tobacco BY-2 cell model, morphological and biochemical studies revealed that mitochondrial reactive oxygen species (ROS) production and mitochondrial dysfunction contribute to sLNT induced PCD. Cell viability, and HO/PI fluorescence imaging and TUNEL assays confirmed a typical cell death process caused by sLNT. Acetylsalicylic acid (an ROS scavenger), diphenylene iodonium (an inhibitor of NADPH oxidases) and protonophore carbonyl cyanide p-trifluoromethoxyphenyl hydrazone (a protonophore and an uncoupler of mitochondrial oxidative phosphorylation) inhibited sLNT-induced H2O2 generation and cell death, suggesting that ROS generation linked, at least partly, to a mitochondrial dysfunction and caspase-like activation. This conclusion was further confirmed by double-stained cells with the mitochondria-specific marker MitoTracker RedCMXRos and the ROS probe H2DCFDA. Moreover, the sLNT-induced PCD of BY-2 cells required cellular metabolism as up-regulation of the AOX family gene transcripts and induction of the SA biosynthesis, the TCA cycle, and miETC related genes were observed. It is concluded that mitochondria play an essential role in the signaling pathway of sLNT-induced ROS generation, which possibly provided new insight into the sLNT-mediated antiviral response, including PCD.

Plant Growth Biostimulants, Dietary Feed Supplements and Cosmetics Formulated with Supercritical CO₂ Algal Extracts

The review paper presents the use of algal extracts as safe and solvent-free components of plant growth biostimulants, dietary feed additives and cosmetics. Innovative technology that uses extracts obtained by supercritical CO₂ extraction, as a method of isolation of biologically active compounds from algal biomass, is presented. An important part of the complete technology is the final formulation of the product. This enabled realization of the further step which was assessment of the utilitarian properties of the extract-based products. The extracts were analysed for the presence of biologically active molecules (e.g., plant hormones, polyphenols) which provide useful properties such as antioxidant, antiviral, anti-inflammatory and antibacterial. The bio-products were tested in germination tests and underwent field trials to search for plant growth biostimulatory properties. Tests on animals (laying hens experiments) were conducted to assess pro-health properties of new dietary feed supplement. Another application were cosmetic formulations (dermatological tests). The results of the application tests were very promising, however further studies are required for the registration of the products and successful implementation to the market.

Global Transcriptome Analysis and Identification of Differentially Expressed Genes in Strawberry after Preharvest Application of Benzothiadiazole and Chitosan

The use of resistance inducers is a novel strategy to elicit defense responses in strawberry fruit to protect against preharvest and postharvest decay. However, the mechanisms behind the specific resistance inducers are not completely understood. Here, global transcriptional changes in strawberry fruit were investigated using RNA-Seq technology. Preharvest, benzothiadiazole (BTH) and chitosan were applied to the plant canopy, and the fruit were harvested at 6, 12, and 24 h post-treatment. Overall, 5,062 and 5,210 differentially expressed genes (fold change ≥ 2) were identified in these fruits under the BTH and chitosan treatments, respectively, as compared to the control expression. About 80% of these genes were differentially expressed by both elicitors. Comprehensive functional enrichment analysis highlighted different gene modulation over time for transcripts associated with photosynthesis and heat-shock proteins, according to elicitor. Up-regulation of genes associated with reprogramming of protein metabolism was observed in fruit treated with both elicitors, which led to increased storage proteins. Several genes associated with the plant immune system, hormone metabolism, systemic acquired resistance, and biotic and abiotic stresses were differentially expressed in treated versus untreated plants. The RNA-Seq output was confirmed using RT-qPCR for 12 selected genes. This study demonstrates that these two elicitors affect cell networks associated with plant defenses in different ways, and suggests a role for chloroplasts as the primary target in this modulation of the plant defense responses, which actively communicate these signals through changes in redox status. The genes identified in this study represent markers to better elucidate plant/pathogen/resistance-inducer interactions, and to plan novel sustainable disease management strategies.

Biological Control beneath the Feet: A Review of Crop Protection against Insect Root Herbivores

Sustainable agriculture is certainly one of the most important challenges at present, considering both human population demography and evidence showing that crop productivity based on chemical control is plateauing. While the environmental and health threats of conventional agriculture are increasing, ecological research is offering promising solutions for crop protection against herbivore pests. While most research has focused on aboveground systems, several major crop pests are uniquely feeding on roots. We here aim at documenting the current and potential use of several biological control agents, including micro-organisms (viruses, bacteria, fungi, and nematodes) and invertebrates included among the macrofauna of soils (arthropods and annelids) that are used against root herbivores. In addition, we discuss the synergistic action of different bio-control agents when co-inoculated in soil and how the induction and priming of plant chemical defense could be synergized with the use of the bio-control agents described above to optimize root pest control. Finally, we highlight the gaps in the research for optimizing a more sustainable management of root pests.

Plant Resistance Inducers against Pathogens in Solanaceae Species-From Molecular Mechanisms to Field Application

This review provides a current summary of plant resistance inducers (PRIs) that have been successfully used in the Solanaceae plant family to protect against pathogens by activating the plant's own defence. Solanaceous species include many important crops such as potato and tomato. We also present findings regarding the molecular processes after application of PRIs, even if the number of such studies still remains limited in this plant family. In general, there is a lack of patterns regarding the efficiency of induced resistance (IR) both between and within solanaceous species. In many cases, a hypersensitivity-like reaction needs to form in order for the PRI to be efficient. "-Omics" studies have already given insight in the complexity of responses, and can explain some of the differences seen in efficacy of PRIs between and within species as well as towards different pathogens. Finally, examples of field applications of PRIs for solanaceous crops are presented and discussed. We predict that PRIs will play a role in future plant protection strategies in Solanaceae crops if they are combined with other means of disease control in different spatial and temporal combinations.

Flavonoid Interaction with a Chitinase from Grape Berry Skin: Protein Identification and Modulation of the Enzymatic Activity

In the present study, an antibody raised against a peptide sequence of rat bilitranslocase (anti-peptide Ab) was tested on microsomal proteins obtained from red grape berry skin. Previously, this antibody had demonstrated to recognize plant membrane proteins associated with flavonoid binding and transport. Immuno-proteomic assays identified a number of proteins reacting with this particular antibody, suggesting that the flavonoid binding and interaction may be extended not only to carriers of these molecules, but also to enzymes with very different functions. One of these proteins is a pathogenesis-related (PR) class IV chitinase, whose in vitro chitinolytic activity was modulated by two of the most representative flavonoids of grape, quercetin and catechin, as assessed by both spectrophotometric and fluorimetric assays in grape microsomes and commercial enzyme preparations. The effect of these flavonoids on the catalysis and its kinetic parameters was also evaluated, evidencing that they determine a hormetic dose-dependent response. These results highlight the importance of flavonoids not only as antioxidants or antimicrobial effectors, but also as modulators of plant growth and stress response. Implications of the present suggestion are here discussed in the light of environment and pesticide-reduction concerns.

Separation and identification of candidate protein elicitors from the cultivation medium of Leptosphaeria maculans inducing resistance in Brassica napus

The Dothideomycete Leptosphaeria maculans, a worldwide fungal pathogen of oilseed rape (Brassica napus), secretes a broad spectrum of molecules into the cultivation medium during growth in vitro. Here, candidate elicitor molecules, which induce resistance in B. napus to L. maculans, were identified in the cultivation medium. The elicitation activity was indicated by increased transcription of pathogenesis-related gene 1 (PR1) and enhanced resistance of B. napus plants to the invasion of L. maculans. The elicitation activity was significantly lowered when the cultivation medium was heated to 80°C. Active components were further characterized by specific cleavage with the proteolytic enzymes trypsin and proteinase K and with glycosidases α-amylase and β-glucanase. The elicitor activity was eliminated by proteolytic digestion while glycosidases had no effect. The filtered medium was fractionated by either ion-exchange chromatography or isoelectric focusing. Mass spectrometry analysis of the most active fractions obtained by both separation procedures revealed predominantly enzymes that can be involved in the degradation of plant cell wall polysaccharides. This is the first study searching for L. maculans-specific secreted elicitors with a potential to be used as defense-activating agents in the protection of B. napus against L. maculans in agriculture. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:918-928, 2016.

Laminarin modulates the chloroplast antioxidant system to enhance abiotic stress tolerance partially through the regulation of the defensin-like gene expression

Algae wall polysaccharide, laminarin (Lam), has an established role on induction of plant disease resistance. In this study, application of Lam increased Arabidopsis fresh weight and enhanced tolerance to salt and heat stress by stabilizing chloroplast under adverse environment. Transcriptome analysis indicated that, in addition to induced a large number of genes associated with the host defense, genes involved in the regulation of abiotic stress tolerance mostly the heat stress response constituted the largest group of the up-regulated genes. Lam induced expression of IRT1, ZIP8, and copper transporters involved in transport of Fe, Zn, Cu ions associated with the activity of chloroplast antioxidant system. Lam also up-regulated genes involved in the synthesis of terpenoid, a plastidial-derived secondary metabolite with antioxidant activity. Overexpression of a Lam-induced defensin like 202 (DEFL202) resulted in increased chloroplast stability under salt stress and increased plant growth activity after heat stress. Expression of antioxidant enzymes including SOD and ascorbate peroxidase (APX), photosystem PsbA-D1 and ABA-dependent responsive to desiccation 22 (RD22) was induced to higher levels in the transgenic seedlings. In sum, our results suggest that Lam is an potent inducer for induction of chloroplastic antioxidant activity. Lam affect plant abiotic stress tolerance partially through regulation of the DEFL-mediated pathway.

Preharvest treatments with chitosan and other alternatives to conventional fungicides to control postharvest decay of strawberry

The effectiveness of the control of postharvest decay of strawberry (Fragaria × ananassa, 'Alba' and 'Romina' cvs.) fruit following field applications of chitosan, laminarin, extracts of Abies spp., Polygonum spp., and Saccharomyces spp., an organic acids and calcium combination, and benzothiadiazole, were compared with a fungicide strategy. These compounds were sprayed every 5 days on the strawberry canopy, from flowering to ripening, in 2012 and 2013. The treatments with alternative compounds provided ∼ 30% reduction in postharvest decay of strawberry compared to the water-treated controls, mainly against gray mold and Rhizopus rot, and without negatively affecting fruit color and firmness. Chitosan and benzothiadiazole were the most effective alternative treatments. Preharvest spraying with these alternative treatments can complement the use of conventional fungicides in the control of postharvest decay of strawberry fruit, especially when disease pressure is low.

Chitin Nanofiber Elucidates the Elicitor Activity of Polymeric Chitin in Plants

Chitin, an N-acetyl-D-glucosamine polymer, is a component of fungal cell walls and a microbe/pathogen-associated molecular pattern that elicits plant defense responses. As polymeric chitin is difficult to handle due to its insolubility in water, many studies on chitin-induced immune responses have used water-soluble low-molecular weight chitin instead. Thus, it is unclear if polymeric chitin can induce resistance. Here, we examined the elicitor activity of chitin nanofiber (CNF) of submicron thickness prepared from polymeric chitin. CNF showed a high dispersing ability in water and induced both reactive oxygen species (ROS) production and chitin-induced defense-related gene expression in Arabidopsis thaliana seedlings. The Arabidopsis chitin elicitor receptor kinase 1 (Atcerk1) mutant, which is impaired in chitin perception, also failed to respond to CNF. CNF exposure triggered ROS generation in suspension-cultured cells from Oryza sativa. Furthermore, pre-treatment of Arabidopsis leaves with CNF effectively reduced pathogen infection by both the fungus Alternaria brassicicola and the bacterium Pseudomonas syringae pv. tomato DC3000. These results demonstrate that CNF has elicitor activity and will help define the role of polymeric chitin in plant immune responses.

Perception of pathogenic or beneficial bacteria and their evasion of host immunity: pattern recognition receptors in the frontline

Plants are continuously monitoring the presence of microorganisms to establish an adapted response. Plants commonly use pattern recognition receptors (PRRs) to perceive microbe- or pathogen-associated molecular patterns (MAMPs/PAMPs) which are microorganism molecular signatures. Located at the plant plasma membrane, the PRRs are generally receptor-like kinases (RLKs) or receptor-like proteins (RLPs). MAMP detection will lead to the establishment of a plant defense program called MAMP-triggered immunity (MTI). In this review, we overview the RLKs and RLPs that assure early recognition and control of pathogenic or beneficial bacteria. We also highlight the crucial function of PRRs during plant-microbe interactions, with a special emphasis on the receptors of the bacterial flagellin and peptidoglycan. In addition, we discuss the multiple strategies used by bacteria to evade PRR-mediated recognition.