Expression Of Defense-related Genes Research Articles

MLP-PG1, a major latex-like protein identified in Cucurbita pepo, confers resistance through the induction of pathogenesis-related genes.

MLP-PG1, identified in Cucurbita pepo, plays a crucial role in resistance against fungal pathogens through the induction of pathogenesis-related genes. MLP-PG1, a major latex-like protein (MLP) from zucchini (Cucurbita pepo), was identified as a transporting factor for hydrophobic organic pollutants. MLPs are members of the Bet v 1 family, similar to pathogenesis-related class 10 proteins (PR-10s). However, the biological functions of MLPs remain unclear. Herein, we show that MLP-PG1 induces the expression of pathogenesis-related (PR) genes and indirectly promotes resistance against pathogens. The activity of the MLP-PG1 promoter in leaves of transgenic tobacco plants was significantly enhanced by inoculation with Pseudomonas syringae pv. tabaci. However, MLP-PG1 did not induce direct resistance through RNase activity. Therefore, we examined the possibility that MLP-PG1 is indirectly involved in resistance; indeed, we found that MLP-PG1 induced the expression of defense-related genes. Overexpression of MLP-PG1 highly upregulated PR-2 and PR-5 and decreased the area of lesions caused by Botrytis cinerea in the leaves of transgenic tobacco plants. Our results demonstrate that MLP-PG1 is involved in indirect resistance against plant diseases, especially caused by fungal pathogens, through the induction of PR genes. This study is the first report to show the induction of PR genes by the expression of MLP from the RNA sequencing analysis and the involvement of MLP-PG1 in the resistance.

MdWRKY61 positively regulates resistance to Colletotrichum siamense in apple (Malus domestica)

Apple trees encounter problems such as stressful environments and pathogen infection throughout their entire growth and development, which limits apple production. WRKY transcription factors play a vital role in the defense against pathogens, but their functions in apple trees need to be further explored. In this study, the MdWRKY61 gene, which encodes the WRKY61 protein of the WRKY group II family, was isolated from GL-3 apple. Tobacco subcellular localization experiments showed that the MdWRKY61 protein is located in the nucleus. Quantitative reverse transcription PCR analysis suggested that MdWRKY61 is highly expressed in the roots and fruits of apples and is rapidly induced in response to salicylic acid, jasmonic acid and Colletotrichum siamense. We obtained MdWRKY61 overexpression lines through Agrobacterium-mediated stable genetic transformation of apple. Subsequent experiments revealed that overexpression of MdWRKY61 increased the resistance of apple to Colletotrichum siamense and promoted the upregulation of defense-related gene expression. Taken together, our data provide insights that MdWRKY61 plays an important role in apple resistance to fungal disease.

A rice gene encoding glycosyl hydrolase plays contrasting roles in immunity depending on the type of pathogens.

Because pathogens use diverse infection strategies, plants cannot use one‐size‐fits‐all defence and modulate defence responses based on the nature of pathogens and pathogenicity mechanism. Here, we report that a rice glycoside hydrolase (GH) plays contrasting roles in defence depending on whether a pathogen is hemibiotrophic or necrotrophic. The Arabidopsis thaliana MORE1 ( Magnaporthe oryzae resistance 1) gene, encoding a member of the GH10 family, is needed for resistance against M. oryzae and Alternaria brassicicola, a fungal pathogen infecting A. thaliana as a necrotroph. Among 13 rice genes homologous to MORE1, 11 genes were induced during the biotrophic or necrotrophic stage of infection by M. oryzae. CRISPR/Cas9‐assisted disruption of one of them (OsMORE1a) enhanced resistance against hemibiotrophic pathogens M. oryzae and Xanthomonas oryzae pv. oryzae but increased susceptibility to Cochliobolus miyabeanus, a necrotrophic fungus, suggesting that OsMORE1a acts as a double‐edged sword depending on the mode of infection (hemibiotrophic vs. necrotrophic). We characterized molecular and cellular changes caused by the loss of MORE1 and OsMORE1a to understand how these genes participate in modulating defence responses. Although the underlying mechanism of action remains unknown, both genes appear to affect the expression of many defence‐related genes. Expression patterns of the GH10 family genes in A. thaliana and rice suggest that other members also participate in pathogen defence.

Impact of Chitosan, Sucrose, Glucose, and Fructose on the Postharvest Decay, Quality, Enzyme Activity, and Defense-Related Gene Expression of Strawberries

Strawberry is one of the most highly consumed fruits worldwide, but is extremely perishable. This study systematically compared the effects of chitosan, sucrose, glucose, and fructose immersion on the physiology and disease development in harvested strawberries. After storage at 15 °C for 9 days, all sugar treatment groups had significantly higher total soluble solids and total anthocyanin content than those of the control group. All sugar treatment groups inhibited malondialdehyde accumulation. At the end of the storage, chitosan, glucose, and fructose maintained higher superoxide dismutase activity and chitosan maintained higher catalase activity. The chitosan and glucose groups had lowest fruit decay index, followed by sucrose and fructose groups. The fruit firmness and luster were better maintained in the glucose group. Furthermore, genes related to sucrose metabolism (e.g., FaSUS1 and FaSUS2), titratable acidity accumulation (e.g., FaMDH1, FaMDH2, FaCS1, and FaCS2), disease resistance (e.g., FaPGIP1, FaWRKY1, and FaWRKY33) and to anabolic jasmonic acid and abscisic acid pathways (e.g., FaJAZ1, FaJAZ2, FaOPR3, FaNCED1, and FaNCED2) were regulated to varying degrees, suggesting that chitosan and glucose participate in plants’ immune signaling networks and regulate disease resistance in fruit through hormone pathways. The findings provide new insights into the physiological regulation of harvested strawberries.

Differential gene expression analyses of ten defence response genes during Fusarium wilt infection in resistant and susceptible pigeonpea cultivars

The present study was undertaken to partly understand the molecular mechanism of defence response during pigeonpea-Fusarium udum interaction. To study the response of defence related gene expression using reverse transcription quantitative real time PCR (RT-qPCR), roots of resistant and susceptible pigeonpea cultivars were infected with F. udum pathogen and samples were collected at 2, 24, 48, and 72 h after inoculation (HAI). PR2, PR10, PAL2, CHS8, IFS1, F3H, LOX, ADC, SPDS, and SPMS were amongst the ten defence response genes studied. The major changes observed in gene expression for all the ten genes are as follows: (i) Out of the ten genes, the expression of three genes, PR2, PR10, and CHS8, peaked at 48 HAI in resistant cultivars compared to susceptible cultivars (ii) the expression of two genes, IFS1 and F3H, was highly induced at all stages in resistant cultivars, while some genotypic differences were observed in susceptible cultivars (iii) the expression of the LOX gene increased only during the early stages at 2 HAI but decreased at later stages in resistant cultivars (iv) In resistant cultivars, the expression of three genes involved in polyamine synthesis, namely ADC, SPDS, and SPMS, peaked at 24 HAI compared to susceptible cultivars. Overall, increased gene expression was found mostly at earlier stages of infection, indicating that these genes are important in providing early resistance to F. udum infection in pigeon pea cultivars. The LOX gene, which codes for the lipooxygenase enzyme, appears to play a role in conferring susceptibility to pigeonea cultivars against F. udum infection, though more research is needed. Further validation studies of all ten genes using overexpression or RNAi technology will provide more information about their roles in the pigeonpea-F.udum interaction.

Tomato and cotton G protein beta subunit mutants display constitutive autoimmune responses.

Heterotrimeric G protein Gβ‐deficient mutants in rice and maize display constitutive immune responses, whereas Arabidopsis Gβ mutants show impaired defense, suggesting the existence of functional differences between monocots and dicots. Using CRISPR/Cas9, we produced one hemizygous tomato line with a mutated SlGB1 Gβ gene. Homozygous slgb1 knockout mutants exhibit all the hallmarks of autoimmune mutants, including development of necrotic lesions, constitutive expression of defense‐related genes, and high endogenous levels of salicylic acid (SA) and reactive oxygen species, resulting in early seedling lethality. Virus‐induced silencing of Gβ in cotton reproduced the symptoms observed in tomato mutants, confirming that the autoimmune phenotype is not limited to monocot species but is also shared by dicots. Even though multiple genes involved in SA and ethylene signaling are highly induced by Gβ silencing in tomato and cotton, co‐silencing of SA or ethylene signaling components in cotton failed to suppress the lethal phenotype, whereas co‐silencing of the oxidative burst oxidase RbohD can repress lethality. Despite the autoimmune response observed in slgb1 mutants, we show that SlGB1 is a positive regulator of the pathogen‐associated molecular pattern (PAMP)‐triggered immunity (PTI) response in tomato. We speculate that the phenotypic differences observed between Arabidopsis and tomato/cotton/rice/maize Gβ knockouts do not necessarily reflect divergences in G protein‐mediated defense mechanisms.

The Wheat Wall-Associated Receptor-Like Kinase TaWAK-6D Mediates Broad Resistance to Two Fungal Pathogens Fusarium pseudograminearum and Rhizoctonia cerealis.

The soil-borne fungi Fusarium pseudograminearum and Rhizoctonia cerealis are the major pathogens for the economically important diseases Fusarium crown rot (FCR) and sharp eyespot of common wheat (Triticum aestivum), respectively. However, there has been no report on the broad resistance of wheat genes against both F. pseudograminearum and R. cerealis. In the current study, we identified TaWAK-6D, a wall-associated kinase (WAK) which is an encoding gene located on chromosome 6D, and demonstrated its broad resistance role in the wheat responses to both F. pseudograminearum and R. cerealis infection. TaWAK-6D transcript induction by F. pseudograminearum and R. cerealis was related to the resistance degree of wheat and the gene expression was significantly induced by exogenous pectin treatment. Silencing of TaWAK-6D compromised wheat resistance to F. pseudograminearum and R. cerealis, and repressed the expression of a serial of wheat defense-related genes. Ectopic expression of TaWAK-6D in Nicotiana benthamiana positively modulated the expression of several defense-related genes. TaWAK-6D protein was determined to localize to the plasma membrane in wheat and N. benthamiana. Collectively, the TaWAK-6D at the plasma membrane mediated the broad resistance responses to both F. pseudograminearum and R. cerealis in wheat at the seedling stage. This study, therefore, concludes that TaWAK-6D is a promising gene for improving wheat broad resistance to FCR and sharp eyespot.

WIPK-NtLTP4 pathway confers resistance to Ralstonia solanacearum in tobacco.

WIPK-NtLTP4 module improves the resistance to R. solanacearum via upregulating the expression of defense-related genes, increasing the antioxidant enzyme activity, and promoting stomatal closure in tobacco. Lipid transfer proteins (LTPs) are a class of small lipid binding proteins that play important roles in biotic and abiotic stresses. The previous study revealed that NtLTP4 positively regulates salt and drought stresses in Nicotiana tabacum. However, the role of NtLTP4 in biotic stress, especially regarding its function in disease resistance remains unclear. Here, the critical role of NtLTP4 in regulating resistance to Ralstonia solanacearum (R. solanacearum), a causal agent of bacterial wilt disease in tobacco, was reported. The NtLTP4-overexpressing lines markedly improved the resistance to R. solanacearum by upregulating the expression of defense-related genes, increasing the antioxidant enzyme activity, and promoting stomatal closure. Moreover, NtLTP4 interacted with wound-induced protein kinase (WIPK; a homolog of MAPK3 in tobacco) and acted in a genetically epistatic manner to WIPK in planta. WIPK could directly phosphorylate NtLTP4 to positively regulate its protein abundance. Taken together, these results broaden the knowledge about the functions of the WIPK-NtLTP4 module in disease resistance and may provide valuable information for improving tobacco plant tolerance to R. solanacearum.

Shoot and root insect herbivory change the plant rhizosphere microbiome and affects cabbage-insect interactions through plant-soil feedback.

Summary Plant–soil feedback (PSF) may influence plant–insect interactions. Although plant defense differs between shoot and root tissues, few studies have examined root‐feeding insect herbivores in a PSF context. We examined here how plant growth and resistance against root‐feeding Delia radicum larvae was influenced by PSF.We conditioned soil with cabbage plants that were infested with herbivores that affect D. radicum through plant‐mediated effects: leaf‐feeding Plutella xylostella caterpillars and Brevicoryne brassicae aphids, root‐feeding D. radicum larvae, and/or added rhizobacterium Pseudomonas simiae WCS417r. We analyzed the rhizosphere microbial community, and in a second set of conspecific plants exposed to conditioned soil, we assessed growth, expression of defense‐related genes, and D. radicum performance.The rhizosphere microbiome differed mainly between shoot and root herbivory treatments. Addition of Pseudomonas simiae did not influence rhizosphere microbiome composition. Plant shoot biomass, gene expression, and plant resistance against D. radicum larvae was affected by PSF in a treatment‐specific manner. Soil conditioning overall reduced plant shoot biomass, Pseudomonas simiae‐amended soil causing the largest growth reduction.In conclusion, shoot and root insect herbivores alter the rhizosphere microbiome differently, with consequences for growth and resistance of plants subsequently exposed to conditioned soil.

Improved defense responses in modern barley cultivars compared to wild relatives against Rhizoctoniasolani

A collection of domesticated and wild barley cultivars was characterized against Rhizoctonia solani, causing foliar and root-rot disease. The defense responses of roots were improved in modern cultivars vs wild genotypes underpinning agronomic selection and domestication. The phenotypic adapted changes, especially in plant biomass, are one of the dependent events associated with these differences between the two groups. In one modern cultivar, the relative expression of defense-related genes was upregulated in root tissues, particularly PR1 (1200-fold) and PR5 (190-fold) genes when challenged with R. solani. Our results have implications for understanding the evolutionary ecology of soil-root rhizosphere interactions and identifying responsive genotypes to be targeted in breeding selection against root pathogens. These studies provide insights into the regulatory mechanisms at the biochemical and transcriptome level to breeding disease resistance, and the possible function of the SA-dependent pathway in the evolution of plant-microbe interactions and immune responses in the rhizosphere of cereals.

Assessing the effects of a novel biostimulant to enhance leafminer resistance and plant growth on common bean

The leafminer Liriomyza trifolii is one of the major insects that affect Phaseolus vulgaris production worldwide. Novel and safe biobased stimulator compound (BSTC) with micronutrient-amino acid chelated compounds was developed from natural compounds and was used for foliar spray of P. vulgaris. Treated plants showed significantly increased in quality and productivity as well as significant reduction in leafminer infestation by close the tunnel end resulting in larvae suffocation and death. BSTC contains chemical composition that has important function in inducing immunity and resistance against insects, enhance plant growth and production. Also, HPLC showed that the assembled BSTC is rich in nucleobases than yeast extract (> 56 fold). Aminochelation zinc enhanced the rate of absorption of nutrient compounds and could participate in safe biofortification strategy. The expression of plant defense related genes under BSTC treatment revealed strong correlations between the transcription rates of defense related genes. Based on binding energies and interacting residues of six vital insect proteins, the best-docked complexes was obtained with disodium 5′-inosinate, delphinidin 3-glucoside and hyperoside. Obtained findings indicate that the foliar application of BSTC can enhance plant growth and productivity, uptake of important elements, expression of defense related genes and inhibit insect essential genes.

The RLK protein TaCRK10 activates wheat high‐temperature seedling‐plant resistance to stripe rust through interacting with TaH2A.1

Plants sense various pathogens and activate immunity responses through receptor-like kinases (RLKs). Cysteine-rich receptor-like kinases (CRKs) are involved in massive transduction pathways upon perception of a pathogen. However, the roles of CRKs in response to stripe rust are unclear. In the present study, we identified a CRK gene (designated TaCRK10) from wheat variety Xiaoyan 6 (XY6) that harbors high-temperature seedling-plant (HTSP) resistance to stripe rust caused by fungal pathogen Puccinia striiformis f. sp. tritici (Pst). The expression level of TaCRK10 was induced by Pst inoculation and high temperature treatment. Knockdown of TaCRK10 by virus-induced gene silencing resulted in attenuated wheat HTSP resistance to Pst, whereas there is no effect on Pst development and host responses under normal temperatures. Notably, overexpression of TaCRK10 in susceptible variety Fielder provided resistance only under normal temperatures at 14 days with reactive oxygen species accumulation and defense-related gene expression of the salicylic acid pathway. Moreover, TaCRK10 physically interacted with and phosphorylated a histone variant TaH2A.1, which belongs to the H2A.W group. Silencing of TaH2A.1 suppressed wheat resistance to Pst, indicating that TaH2A.1 plays a positive role in wheat resistance to Pst. Thus, TaCRK10 serves as an important sensor of Pst infection and high temperatures, and it activates wheat resistance to Pst through regulating nuclear processes. This knowledge helps elucidate the molecular mechanism of wheat HTSP resistance to Pst and promotes efforts in developing wheat varieties with resistance to stripe rust.

Arabidopsis MED18 Interaction With RNA Pol IV and V Subunit NRPD2a in Transcriptional Regulation of Plant Immune Responses.

Mediator is a conserved multiprotein complex important for transcription by RNA polymerase II (Pol II). Arabidopsis Mediator subunit MED18 regulates flowering, hormone signaling and plant immunity. Here we report that Arabidopsis MED18 interacted with NUCLEAR RNA POLYMERASE D2a (NRPD2a), the second largest subunit of the nuclear Pol IV and V, which function in RNA-directed DNA methylation and epigenetic regulation of gene expression. Mutants for both MED18 and NRPD2a were compromised in resistance to necrotrophic fungal pathogen Botrytis cinerea. Mutants for NRPD1a, the largest subunit of Pol IV, were also compromised in resistance to Botrytis, supporting a critical role of Pol IV and V in plant defense against Botrytis. Increased Botrytis susceptibility of both the med18 and nrpd2a mutants were associated with reduced accumulation of reactive oxygen species, which are known to promote resistance to Botrytis. Both the basal and pathogen-induced levels of salicylic acid and jasmonic acid were also significantly altered in the med18 and nrpd2a mutants. Transcriptome profiling found that MED18 and NRPD2a affected both unique and overlapping sets of genes in a broad spectrum of biological processes and pathways that influence plant–pathogen interaction. The genes altered in expression in the med18 and nrpd2a mutants include disease resistance proteins, salicylic acid and jasmonic acid signaling and responses, which are known to affect resistance to necrotrophic pathogens. The novel interaction between subunits of Mediator and plant-specific RNA polymerases provides a new mechanism for epigenetic regulation of resistance and expression of defense-related genes in plant immunity.

Verticillium klebahnii and V. isaacii Isolates Exhibit Host-Dependent Biological Control of Verticillium Wilt Caused by V. dahliae

Verticillium dahliae, the soilborne fungal pathogen, causes vascular wilt on many economically important crops, resulting in significant yield losses. V. klebahnii (isolate PD659) and V. isaacii (isolate PD660), two related species that cause few or no symptoms in some hosts, were evaluated as potential biocontrol agents (BCAs) in eggplant, lettuce, and tomato by pre-, post-, and coinoculation with a virulent race 1 isolate of V. dahliae (VdLs16). Initial studies demonstrated that the biocontrol efficacy of both BCAs was similar to reference BCA Talaromyces flavus (NRRL15936) across all hosts (α = 0.05). Subsequent experiments with PD659 against V. dahliae isolate Sm113 from eggplant, VdLs16 and VdLs17 isolates from lettuce, and Le1811 isolate from tomato demonstrated a significant biocontrol efficacy in eggplant and tomato but not in lettuce (at 95% confidence interval), suggesting host-dependent effectiveness of V. klebahnii. Confocal microscopy using green fluorescent protein-tagged tomato V. dahliae isolate Le1811 indicated delayed xylem colonization or lack of pathogen progression into the vascular system in a host-dependent manner on BCA-treated plants. Quantitative analyses of the expression of defense-related genes PR1a, PR5, acidic extracellular β-1,3-glucanase (GlucA), basic intracellular β-1,3-glucanase (GlucB), acidic extracellular chitinase (Chi3), basic intracellular chitinase (Chi9), and cysteine proteases (cysProteases) in tomato in the presence or absence of PD659 suggested an elevated expression of defense-related genes in compatible interaction of V. dahliae–tomato cultivar Early Pak. V. klebahnii (PD659) may delay the entry of V. dahliae by competing for space or nutrients during the initial stages of root colonization. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Temperature-dependent sugar accumulation in interspecific Capsicum F1 plants showing hybrid weakness.

In plants, F1 hybrids showing hybrid weakness exhibit weaker growth than their parents. The phenotypes of hybrid weakness are often suppressed at certain temperatures. However, it is unclear whether hybrid weakness in Capsicum annuum × C. chinense is temperature-dependent or not. Our study showed that Capsicum hybrid weakness was suppressed at 30 and 35°C and was induced at 15, 20, and 25°C. Moreover, we investigated the time course of hybrid weakness in cell death, metabolite content, and gene expression in leaves of plants transferred to 20°C after growing at 30°C for 21 days. The expression of pathogen defense-related genes was upregulated at1day after transfer to 20°C (DAT). Cell death was detected at 7 DAT, plant growth had almost stopped since 14 DAT, and sugars were accumulated at 42 DAT in hybrid plants. The study revealed that some sugar transporter genes, which had been upregulated since 7 DAT, were involved in sugar accumulation in Capsicum hybrid weakness. Thus, our results demonstrated that gene expression changes occur first, followed by physiological and morphological changes after induction of hybrid weakness. These responses observed in this study in Capsicum hybrid weakness are likely to be owed to plant defense responses-like reactions.

Melatonin enhances the resistance of ginger rhizomes to postharvest fungal decay

Significant losses in harvested ginger can be directly attributed to decay fungi, including Fusarium oxysporum and Penicillium brevicompactum. Eco-friendly treatments, utilizing non-conventional chemical methods to manage postharvest decay on ginger rhizome are being actively investigated. In the current study, the application of melatonin (N-acetyl-5-methoxytryptamine) was evaluated for controlling postharvest decay of ginger rhizomes, artificially-inoculated with F. oxysporum or P. brevicompactum. Results showed that the melatonin treatment (0.1 mM, 15-min immersion) reduced F. oxysporum and P. brevicompactum rots on rhizomes. Melatonin induced the expression of defense-related genes, including β-1,3-glucanase (GLU), phenylalanine ammonia-lyase (PAL), and coiled-coil nucleotide-binding site leucine-rich repeat (CC-NBS-LRR). GLU and PAL enzyme activity was also induced in ginger rhizomes, and the level of total phenols in rhizomes was elevated. Importantly, melatonin did not have a negative impact on rhizome quality. The ability of melatonin to enhance disease resistance may be partially attributed to the induction of defense response in ginger rhizomes. The findings of the present study have practical implications for the use of melatonin to reduce postharvest decays in ginger rhizomes.

Leaf and tuber treatments with PAMPs trigger organ-specific responses in potato

Organ-specificity of plant defence is an under-represented axis of research in plant biology. However, recent publications point out the importance of this concept in plant–pathogen interactions. Indeed, assuming the resistance status of a whole plant against a given pathogen following studies conducted on a single organ might lead to erroneous conclusions. This study aims at understanding the extent of potato (Solanum tuberosum) organ-specific defence mechanisms after leaf and tuber treatments with pathogen-associated molecular patterns (PAMPs). Our results show that potato leaves and tubers activate contrasting defence responses, in terms of production of reactive oxygen species (ROS) and activation of defence-related genes, following treatments with the Phytophthora PAMP Pep-25 or the bacterial PAMP flg22. Interestingly, flg22 induced ROS production in both leaves and tubers, indicating that this peptide is recognized in these organs. By contrast, ROS production was induced in the leaf but not in the tuber after Pep-25 treatment. Analysis of changes in expression of defence-related genes showed that at least six genes exhibited organ-specific expression patterns. In addition to those early responses, inhibition of potato seedling growth was also found to affect both the aboveground and belowground organs following treatment with Pep-25 and with flg22. Taken together, these experiments will help further the investigation of potato defence against Phytophthora spp.

Defense Response to Hemileia vastatrix in Susceptible Grafts onto Resistant Rootstock of Coffea arabica L.

The use of resistant cultivars and fungicides are common methods to control coffee leaf rust (CLR), the main disease that affects the Arabica coffee crop. In this study, we evaluated the response of grafted and ungrafted plants during the early stage of Hemileia vastatrix infection. We used ungrafted plants of Oro Azteca (resistant cultivar) and Garnica (susceptible cultivar), and grafted plants, combining both as rootstock and graft (Garnica/Oro Azteca and Oro Azteca/Garnica). All plants were inoculated with H. vastatrix uredospores, and we quantified the development of fungal structures in the leaf tissue of inoculated plants using qRT-PCR to measure relative expression of two pathogenesis recognition genes (CaNDR1 and CaNBS-LRR) and three genes associated with the salicylic acid (SA) pathway (CaNPR1, CaPR1 and CaPR5). In Garnica grafted on Oro Azteca, the fungal structures recorded were significantly less than in Garnica ungrafted plants. In addition, the expression of defense-related genes in grafted plants was higher than in ungrafted plants. Our results indicate that the defense response to CLR is strongly influenced by the rootstock employed.

The Flower-Infecting Fungus Ustilaginoidea virens Subverts Plant Immunity by Secreting a Chitin-Binding Protein.

Ustilaginoidea virens is a biotrophic fungal pathogen specifically colonizing rice floral organ and causes false smut disease of rice. This disease has emerged as a serious problem that hinders the application of high-yield rice cultivars, by reducing grain yield and quality as well as introducing mycotoxins. However, the pathogenic mechanisms of U. virens are still enigmatic. Here we demonstrate that U. virens employs a secreted protein UvCBP1 to manipulate plant immunity. In planta expression of UvCBP1 led to compromised chitin-induced defense responses in Arabidopsis and rice, including burst of reactive oxygen species (ROS), callose deposition, and expression of defense-related genes. In vitro-purified UvCBP1 protein competes with rice chitin receptor OsCEBiP to bind to free chitin, thus impairing chitin-triggered rice immunity. Moreover, UvCBP1 could significantly promote infection of U. virens in rice flowers. Our results uncover a mechanism of a floral fungus suppressing plant immunity and pinpoint a universal role of chitin-battlefield during plant–fungi interactions.

Exogenously Applied Chitosan and Chitosan Nanoparticles Improved Apple Fruit Resistance to Blue Mold, Upregulated Defense-Related Genes Expression, and Maintained Fruit Quality

Blue rot disease caused by Penicillium expansum is one of the most widespread fungal diseases that affects apples worldwide. This work was to verify the effect of chitosan (2 and 4 g/L) and its nano-form (0.2 and 0.4 g/L) against blue rot disease on apples and their effect on the expression of six defense-related genes as well as fruit quality parameters. Regarding disease incidence, in most cases, chitosan NPs performed better as compared to their raw materials for both artificial and natural infections. The highest efficacy was obtained for chitosan NPs at 0.4 g/L for artificial and natural infection in both 2019 and 2020 seasons. All treatments kept fruit quality parameters regarding firmness, total soluble solids, and titratable acidity for artificial and natural infection in both seasons. As expected, the exogenous application of chitosan NPs and bulk form triggered an increase in the expression levels of six defense-related genes including chitinase, peroxidase, β-1,3-glucanase, Xyloglucan endotransglycosylase (XET), pathogenesis-related protein (PR8), and phenylalanine ammonia lyase-1 (PAL1). Moreover, the highest mRNA quantity of all the studied genes was detected in leaves treated with chitosan NPs at both concentrations compared to other treatments. Chitosan NPs can be considered an eco-friendly and effective approach against blue mold of apples and can be integrated into management programs to maintain postharvest quality and extend the shelf life of fruits.