Eliciting transcriptomic and antioxidant defensive responses against Rhizoctonia root rot of sorghum using the endophyte Aspergillus oryzae YRA3.

Environmental pollution due to the improper use of the chemical fungicides represents a vital ecological problem, which affects human and animal health, as well as the microbial biodiversity and abundance in the soil. In this study, an endophytic fungus Aspergillus oryzae YRA3, isolated from the wild plant Atractylis carduus (Forssk.) C.Chr, was tested for its biocontrol activity against Rhizoctonia root rot of sorghum. The antagonistic potential of A. oryzae YRA3 was tested against Rhizoctonia solani in vitro. A full inhibition in the growth of R. solani was recorded indicating a strong antagonistic potential for this endophyte. To investigate the chemical composition of its metabolites, GC/MS analysis was used and thirty-two compounds in its culture filtrate were identified. Among these metabolites, some compounds with an antifungal background were detected including palmitic acid, 2-heptanone, and 2,3-butanediol. To these antifungal metabolites the antagonistic activity of A. oryzae YRA3 can be attributed. In the greenhouse experiment, treating of the infected sorghum plants with A. oryzae YRA3 significantly reduced severity of the Rhizoctonia root rot by 73.4%. An upregulation of the defensive genes (JERF3), (POD) and (CHI II) was recorded in sorghum roots when were inoculated with A. oryzae YRA3. In addition, an increment in the activity of peroxidase and polyphenol oxidase, as well as the total phenolic content in the sorghum roots was also recorded. Furthermore, the results obtained from the greenhouse experiment revealed a growth-promoting effect for inoculating the sorghum plants with A. oryzae YRA3. It can be concluded that A. oryzae YRA3 can be a probable biological agent to control this disease in sorghum. However, its evaluation under field conditions is highly needed in the future studies.

Taxonomical, functional, and cytopathological characterization of Bacillus spp. from Lake Magadi, Kenya, against Rhizoctonia solani Kühn in Phaseolus vulgaris L.

A decline in common bean production and the ineffectiveness of synthetic chemical products in managing plant pathogens has led to exploiting Kenyan soda lakes as an alternative search for biocontrol agents. This study aimed to identify phylogenetically Bacillus spp. from Lake Magadi and their antagonistic activity against Rhizoctonia solani under in vitro and in vivo conditions. The 16 S ribosomal RNA (rRNA) subunit sequences of six bacterial strains isolated from Lake Magadi showed diversity similar to the Bacillus genus; Bacillus velezensis, Bacillus subtilis, and Bacillus pumilus. In vitro, antagonism showed varied mycelium inhibition rates of fungi in the coculture method. Enzymatic assays showed the varied ability of isolates to produce phosphatase, pectinase, chitinase, protease, indole-3-acetic acid (IAA), and hydrogen cyanide (HCD). The in vivo assay showed M09 (B. velezensis) with the lowest root mortality and incidence of postemergence wilt. Pre-emergence wilt incidence was recorded as lowest in M10 (B. subtilis). Isolate M10 had the highest phenylalanine ammonia-lyase (PAL) for defense enzymes, while polyphenol oxidase (PPO) and peroxidase were recorded as highest in M09. For the phenolic content, M10 recorded the highest phenolic content. In conclusion, Lake Magadi harbors Bacillus spp, which can be used as a potential biocontrol of R. solani.

Biochemical defense mechanism associated with host-specific disease resistance pathways against Rhizoctonia solani AG3-PT potatoes canker disease.

MAIN CONCLUSION: Screening for resistance in 40 potato genotypes to Rhizoctonia solani AG-3PT-stem-canker, antioxidant enzymes activity as well as total phenol compounds were documented. Rhizoctonia solani AG-3PT-stem-canker is one of the most devastating diseases that leads to severe economic losses in potatoes, Solanum tuberosum globally. Crop management and eugenic practices, especially the use of resistance can be effective in reducing the disease incidence. However, the information about potato-R. Solani interaction is still limited. This study explored screening for resistance in forty potato genotypes to R. solani, analyzing biomass growth parameters (BGPs), as well as antioxidant enzymes activity of which peroxidase/peroxide-reductases (POXs), superoxide dismutase (SOD), polyphenol oxidase (PPO), catalase (CAT), phenylalanine ammonia-lyase (PAL), ß-1,3-glucanase (GLU) and total phenol compounds (TPCs) were taken into account. In addition, we analyzed up-regulation of two gene markers (PR-1 and Osmotin), using reverse transcription quantitative PCR (RT-qPCR). For which, the resistant 'Savalan', partially resistant 'Agria', partially susceptible 'Sagita' and susceptible 'Pashandi' were selected to explore the trails in their roots and leaves over the time courses of 1, 2 and 3-weeks post inoculation (wpi) following inoculation. Cluster analysis divided potatoes into four distinct groups, based on disease severity scales (0-100%) significance. The BGPs, shoot and root length, fresh and dry weight, and root volume were also significantly higher in infected potatoes compared to non-inoculated controls. Antioxidant enzymes activity also indicated the highest increased levels for POX (fourfold at 3wpi), CAT (1.5-fold at 3wpi), SOD (6.8-fold at 1wpi), and PAL (2.7-fold at 3wpi) in the resistant genotype, 'Savalan', whereas the highest activity was recorded in TPC (twofold at 1 wpi), PPO (threefold at 3wpi), and GLU (2.3-fold at 1wpi) in partially resistant genotypes. Although the defense-related enzymatic activities were sharply elevated in the resistant and partially resistant genotypes following inoculation, no significant correlations were between the activity trends of the related enzymes. The two related gene markers also showed comprehensive transcriptional responses up to 3.4-fold, predominantly in resistant genotypes. Surprisingly, the PR-1 gene marker, basically resistant to Wilting agent Verticillium dahlia was overexpressed in resistant 'Savalan' and 'Agria' against R. solani AG3-PT. Similar results were obtained on Osmotin gene marker resistant to late-blight P. infestans, and early-blight Alternaria solani that similarly modulates immunity against R. solani. Furthermore, there was a significant correlation between resistance, enzyme activity, and gene expression in the aforesaid cultivars. Studying the physiological metabolic pathways of antioxidant enzymes activity appears to be an important direction in research to elucidate resistance to R. solani in potatoes.

Defense Surveillance System at the Interface: Response of Rice Towards Rhizoctonia solani During Sheath Blight Infection.

Sheath blight of rice caused by necrotrophic plant pathogen Rhizoctonia solani is one of the most common fungal diseases of rice leading to significant yield loss. Among the defense responses exhibited by the host plants towards fungal infections, those functional within the apoplast contribute significantly. Here, we have studied apoplastic defense response of rice towards R. solani during sheath blight infection. The transcriptome of R. solani-infected rice plants was compared with that of uninfected rice, to identify the set of defense genes that undergo differential expression and code for proteins with a predicted N-terminal signal peptide. Significant changes in the stress-responsive, molecular signal perception, protein modification, and metabolic process pathways represented by a group of differentially expressed genes were observed. Our data also revealed two secreted protease inhibitors from rice that exhibit increased expression during R. solani infection and induce disease resistance when expressed in Nicotiana benthamiana. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The RsRlpA Effector Is a Protease Inhibitor Promoting Rhizoctonia solani Virulence through Suppression of the Hypersensitive Response.

Rhizoctonia solani (Rs) is a soil-borne pathogen with a broad host range. This pathogen incites a wide range of disease symptoms. Knowledge regarding its infection process is fragmented, a typical feature for basidiomycetes. In this study, we aimed at identifying potential fungal effectors and their function. From a group of 11 predicted single gene effectors, a rare lipoprotein A (RsRlpA), from a strain attacking sugar beet was analyzed. The RsRlpA gene was highly induced upon early-stage infection of sugar beet seedlings, and heterologous expression in Cercospora beticola demonstrated involvement in virulence. It was also able to suppress the hypersensitive response (HR) induced by the Avr4/Cf4 complex in transgenic Nicotiana benthamiana plants and functioned as an active protease inhibitor able to suppress Reactive Oxygen Species (ROS) burst. This effector contains a double-psi beta-barrel (DPBB) fold domain, and a conserved serine at position 120 in the DPBB fold domain was found to be crucial for HR suppression. Overall, R. solani seems to be capable of inducing an initial biotrophic stage upon infection, suppressing basal immune responses, followed by a switch to necrotrophic growth. However, regulatory mechanisms between the different lifestyles are still unknown.

Evaluation of plant growth promotion properties and induction of antioxidative defense mechanism by tea rhizobacteria of Darjeeling, India.

A total of 120 rhizobacteria were isolated from seven different tea estates of Darjeeling, West Bengal, India. Based on a functional screening of in vitro plant growth-promoting (PGP) activities, thirty potential rhizobacterial isolates were selected for in-planta evaluation of PGP activities in rice and maize crops. All the thirty rhizobacterial isolates were identified using partial 16S rRNA gene sequencing. Out of thirty rhizobacteria, sixteen (53.3%) isolates belong to genus Bacillus, five (16.6%) represent genus Staphylococcus, three (10%) represent genus Ochrobactrum, and one (3.3%) isolate each belongs to genera Pseudomonas, Lysinibacillus, Micrococcus, Leifsonia, Exiguobacterium, and Arthrobacter. Treatment of rice and maize seedlings with these thirty rhizobacterial isolates resulted in growth promotion. Besides, rhizobacterial treatment in rice triggered enzymatic [ascorbate peroxidase (APX), catalase (CAT), chitinase, and phenylalanine ammonia-lyase (PAL)], and non-enzymatic [proline and polyphenolics] antioxidative defense reactions indicating their possible role in the reduction of reactive oxygen species (ROS) burden and thereby priming of plants towards stress mitigation. To understand such a possibility, we tested the effect of rhizobacterial consortia on biotic stress tolerance of rice against necrotrophic fungi, Rhizoctonia solani AG1-IA. Our results indicated that the pretreatment with rhizobacterial consortia increased resistance of the rice plants towards the common foliar pathogen like R. solani AG1-IA. This study supports the idea of the application of plant growth-promoting rhizobacterial consortia in sustainable crop practice through the management of biotic stress under field conditions.

The Cysteine-Rich Repeat Protein TaCRR1 Participates in Defense against Both Rhizoctonia cerealis and Bipolaris sorokiniana in Wheat.

The domain of unknown function 26 (DUF26), harboring a conserved cysteine-rich motif (C-X8-C-X2-C), is unique to land plants. Several cysteine-rich repeat proteins (CRRs), belonging to DUF26-containing proteins, have been implicated in the defense against fungal pathogens in ginkgo, cotton, and maize. However, little is known about the functional roles of CRRs in the important staple crop wheat (Triticum aestivum). In this study, we identified a wheat CRR-encoding gene TaCRR1 through transcriptomic analysis, and dissected the defense role of TaCRR1 against the soil-borne fungi Rhizoctonia cerealis and Bipolaris sorokiniana, causal pathogens of destructive wheat diseases. TaCRR1 transcription was up-regulated in wheat towards B. Sorokiniana or R. cerealis infection. The deduced TaCRR1 protein contained a signal peptide and two DUF26 domains. Heterologously-expressed TaCRR1 protein markedly inhibited the mycelia growth of B. sorokiniana and R. cerealis. Furthermore, the silencing of TaCRR1 both impaired host resistance to B. sorokiniana and R. cerealis and repressed the expression of several pathogenesis-related genes in wheat. These results suggest that the TaCRR1 positively participated in wheat defense against both B. sorokiniana and R. cerealis through its antifungal activity and modulating expression of pathogenesis-related genes. Thus, TaCRR1 is a candidate gene for improving wheat resistance to B. sorokiniana and R. cerealis.

Inhibition of Rhizoctonia solani RhCh-14 and Pythium ultimum PyFr-14 by Paenibacillus polymyxa NMA1017 and Burkholderia cenocepacia CACua-24: A proposal for biocontrol of phytopathogenic fungi.

Biocontrol has emerged in recent years as an alternative to pesticides. Given the importance of environmental preservation using biocontrol, in this study two antagonistic bacteria against phytopathogenic fungi were isolated and evaluated. These bacterial strains, identified as Paenibacillus polymyxa NMA1017 and Burkholderia cenocepacia CACua-24, inhibited (70 to 80%) the development of two phytopathogens of economic importance: the fungus Rhizoctonia solani RhCh-14, isolated from chili pepper, and the oomycete Pythium ultimum PyFr-14, isolated from tomato. The spectrum was not limited to the previous pathogens, but also to other phytopathogenic fungus, some bacteria and other oomycetes. Fungi-bacteria microcultures observed with optical and scanning electron microscopy revealed hyphae disintegration and pores formation. The antifungal activity was found also in the supernatant, suggesting a diffusible compound is present. Innocuous tests on tobacco leaves, blood agar, bean seed germination and in Galleria mellonella larvae showed that strain NMA1017 has the potential to be a biocontrol agent. Greenhouse experiments with bean plants inoculated with P. polymyxa exhibited the efficacy to inhibit the growth of R. solani and P. ultimum. Furthermore, P. polymyxa NMA1017 showed plant growth promotion activities, such as siderophore synthesis and nitrogen fixation which can contribute to the crop development.

Co-inoculation of different antagonists can enhance the biocontrol activity against Rhizoctonia solani in tomato.

Biological control by using microbial inoculants is adopted as the best alternative to chemical pesticides to manage plant diseases. In the present study, a microbial consortia based management strategy involving the microbes Bacillus velezensis MB101 (BV), Streptomyces atrovirens N23 (SA) and Trichoderma lixii NAIMCC-F-01760 (TL), was evaluated for the management of Rhizoctonia solani (RS), the causal agent of tomato root rot. The efficacy of these microbial inoculants was evaluated in glasshouse and field experiments. Plant defense-related enzymes were assayed in the glasshouse, and biocontrol effect was evaluated in the field with RS infected soil. In the glasshouse experiment, co-inoculated SA + TL treated plants showed maximum disease resistance in comparison to control. Also, the plant defense-related enzymes such as chitinase, ß-1,3-glucanase, peroxidases, polyphenol oxidase, and phenylalanine ammonia lyase were increased in this treatment. Furthermore, three application methods were assessed in the field, and SA + TL showed maximum disease reduction (76%) by the dual application. Based on glasshouse and field study results, it was concluded that co-inoculation of SA + TL activated plant defense against RS as compared to the individual microbes, and co-inoculation could be a new effective strategy to manage the root rot pathogen in an eco-compatible manner.

First report of a novel alphapartitivirus in the basidiomycete Rhizoctonia oryzae-sativae.

Rhizoctonia oryzae-sativae is a soil-borne basidiomycete fungus that causes aggregate sheath spot disease on rice worldwide. Here, we report the complete genome sequence of a partitivirus designated as Rhizoctonia oryzae-sativae partitivirus 1 (RosPV1) infecting this fungus. The genome of RosPV1 consists of two double-stranded RNA (dsRNA) segments. The larger segment, designated as dsRNA-1 (1,961 bp), contains a single open reading frame (ORF) that encodes a putative polypeptide with a conserved RNA-dependent RNA polymerase (RdRp) domain. The smaller segment, dsRNA-2 (1,819 bp), also has a single ORF, which is predicted to encode the capsid protein (CP). BLAST searches and phylogenetic analyses suggested that RosPV1 is a representative member of a new species within the genus Alphapartitivirus. This is the first report of an alphapartitivirus infecting the fungus R. oryzae-sativae.

RAVL1 Activates Brassinosteroids and Ethylene Signaling to Modulate Response to Sheath Blight Disease in Rice.

Rhizoctonia solani causes sheath blight disease in rice; however, the defense mechanism of rice plants against R. solani remains elusive. To analyze the roles of brassinosteroid (BR) and ethylene signaling on rice defense to R. solani, wild-type (WT) rice and several mutants and overexpressing (OX) lines were inoculated with R. solani. Mutants d61-1 and d2 were less susceptible to sheath blight disease, bri1-D was more susceptible, and ravl1 and d61-1/EIL1 Ri5 were similarly susceptible compared with WT. The double mutant ravl1/d61-1 was phenotypically similar to the ravl1 mutant. Transcriptome analysis, chromatin immunoprecipitation assay, electrophoretic mobility shift assay, and transient assays indicted that RAVL1 might directly activate Ethylene insensitive 3-like 1 (EIL1), a master regulator of ethylene signaling. Mutants ers1 and d61-1/RAVL1 OX were resistant to sheath blight disease, whereas EIL1 RNAi mutants and RAVL1 OX were more susceptible than WT. BRI1 and D2 expression in EIL1 Ri5/RAVL1 OX and EIL1 expression in d61-1/RAVL1 OX indicated that RAVL1 activates BRI1/D2 and EIL1, respectively, independent of BR and ethylene signaling. Our analyses provide information on how BR and ethylene signaling regulate sheath blight disease and on the regulatory function of RAVL1 in rice sheath blight disease.

Deep Sequencing Uncovers Rice Long siRNAs and Its Involvement in Immunity Against Rhizoctonia solani.

Small RNA (sRNA) is a class of noncoding RNA that can silence the expression of target genes. In rice, the majority of characterized sRNAs are within the range of 21 to 24 nucleotides (nt) long, whose biogenesis and function are associated with a specific sets of components, such as Dicer-like (OsDCLs) and Argonaute proteins (OsAGOs). Rice sRNAs longer than 24 nt are occasionally reported, with biogenesis and functional mechanism uninvestigated, especially in a context of defense responses against pathogen infection. By using deep sequencing, we identified a group of rice long small interfering RNAs (lsiRNAs) that are within the range of 25 to 40 nt in length. Our results show that some rice lsiRNAs are differentially expressed upon infection of Rhizoctonia solani, the causal agent of the rice sheath blight disease. Bioinformatic analysis and experimental validation indicate that some rice lsiRNAs can target defense-related genes. We further demonstrate that rice lsiRNAs are neither derived from RNA degradation nor originated as secondary small interfering RNAs (siRNAs). Moreover, lsiRNAs require OsDCL4 for biogenesis and OsAGO18 for function. Therefore, our study indicates that rice lsiRNAs are a unique class of endogenous sRNAs produced in rice, which may participate in response against pathogens.

Ethylene Signaling Is Important for Isoflavonoid-Mediated Resistance to Rhizoctonia solani in Roots of Medicago truncatula.

The root-infecting necrotrophic fungal pathogen Rhizoctoniasolani causes significant disease to all the world's major food crops. As a model for pathogenesis of legumes, we have examined the interaction of R. solani AG8 with Medicago truncatula. RNAseq analysis of the moderately resistant M. truncatula accession A17 and highly susceptible sickle (skl) mutant (defective in ethylene sensing) identified major early transcriptional reprogramming in A17. Responses specific to A17 included components of ethylene signaling, reactive oxygen species metabolism, and consistent upregulation of the isoflavonoid biosynthesis pathway. Mass spectrometry revealed accumulation of the isoflavonoid-related compounds liquiritigenin, formononetin, medicarpin, and biochanin A in A17. Overexpression of an isoflavone synthase in M. truncatula roots increased isoflavonoid accumulation and resistance to R. solani. Addition of exogenous medicarpin suggested this phytoalexin may be one of several isoflavonoids required to contribute to resistance to R. solani. Together, these results provide evidence for the role of ethylene-mediated accumulation of isoflavonoids during defense against root pathogens in legumes. The involvement of ethylene signaling and isoflavonoids in the regulation of both symbiont-legume and pathogen-legume interactions in the same tissue may suggest tight regulation of these responses are required in the root tissue.

Metabolomic study of two rice lines infected by Rhizoctonia solani in negative ion mode by CE/TOF-MS.

Rhizoctonia solani is a fungal pathogen that causes sheath blight disease in rice plants. In this study, metabolomic analysis using CE/TOF-MS in negative ion mode was used to investigate the resistance response of resistant and susceptible rice lines (32R and 29S, respectively) due to R. solani infection. Two rice lines showed different responses to the infection of R. solani. In 32R, R. solani infection induced significant increases in adenosine diphosphate (ADP), glyceric acid, mucic acid and jasmonic acid. In 29S, inosine monophosphate (IMP) was involved in the plant response to R. solani infection. Phenol compounds showed an increase as a response of the rice lines to R. solani infection. The study suggests that R. solani infection effects in 32R are associated with the induction of plant metabolic processes such as respiration, photorespiration, pectin synthesis, and lignin accumulation. In 29S, the R. solani infection is suggested to correlate with nitrogen metabolism.

Antibiosis functions during interactions of Trichoderma afroharzianum and Trichoderma gamsii with plant pathogenic Rhizoctonia and Pythium.

Trichoderma afroharzianum is one of the best characterized Trichoderma species, and strains have been utilized as plant disease suppressive inoculants. In contrast, Trichoderma gamsii has only recently been described, and there is limited knowledge of its disease suppressive efficacies. Comparative studies of changes in gene expression during interactions of these species with their target plant pathogens will provide fundamental information on pathogen antibiosis functions. In the present study, we used complementary DNA amplified fragment length polymorphism (cDNA-AFLP) analysis to investigate changes in transcript profiling of T. afroharzianum strain LTR-2 and T. gamsii strain Tk7a during in vitro interactions with plant pathogenic Rhizoctonia solani and Pythium irregulare. Considerable differences were resolved in the overall expression profiles of strains LTR-2 and Tk7a when challenged with either plant pathogen. In strain LTR-2, previously reported mycoparasitism-related genes such as chitinase, polyketide synthase, and non-ribosomal peptide synthetase were found to be differentially expressed. This was not so for strain Tk7a, with the only previously reported antibiosis-associated genes being small secreted cysteine-rich proteins. Although only one differentially expressed gene was common to both strains LTR-2 and Tk7a, numerous genes reportedly associated with pathogen antibiosis processes were differentially expressed in both strains, including degradative enzymes and membrane transport proteins. A number of novel potential antibiosis-related transcripts were found from strains LTR-2 and Tk7a and remain to be identified. The expression kinetics of 20 Trichoderma (10 from strain LTR-2, 10 from strain Tk7a) transcript-derived fragments (TDFs) were quantified by quantitative reverse transcription PCR (RT-qPCR) at pre- and post-mycelia contact stages of Trichoderma-prey interactions, thereby confirming differential gene expression. Collectively, this research is providing information to elucidate the antibiosis mechanisms and disease suppressive activities of T. afroharzianum and T. gamsii against soilborne fungal and oomycete plant pathogens.

Stress-Responsive Expression, Subcellular Localization and Protein-Protein Interactions of the Rice Metacaspase Family.

Metacaspases, a class of cysteine-dependent proteases like caspases in animals, are important regulators of programmed cell death (PCD) during development and stress responses in plants. The present study was focused on comprehensive analyses of expression patterns of the rice metacaspase (OsMC) genes in response to abiotic and biotic stresses and stress-related hormones. Results indicate that members of the OsMC family displayed differential expression patterns in response to abiotic (e.g., drought, salt, cold, and heat) and biotic (e.g., infection by Magnaporthe oryzae, Xanthomonas oryzae pv. oryzae and Rhizoctonia solani) stresses and stress-related hormones such as abscisic acid, salicylic acid, jasmonic acid, and 1-amino cyclopropane-1-carboxylic acid (a precursor of ethylene), although the responsiveness to these stresses or hormones varies to some extent. Subcellular localization analyses revealed that OsMC1 was solely localized and OsMC2 was mainly localized in the nucleus. Whereas OsMC3, OsMC4, and OsMC7 were evenly distributed in the cells, OsMC5, OsMC6, and OsMC8 were localized in cytoplasm. OsMC1 interacted with OsLSD1 and OsLSD3 while OsMC3 only interacted with OsLSD1 and that the zinc finger domain in OsMC1 is responsible for the interaction activity. The systematic expression and biochemical analyses of the OsMC family provide valuable information for further functional studies on the biological roles of OsMCs in PCD that is related to abiotic and biotic stress responses.

Pathogen-induced SGT1 of Arachis diogoi induces cell death and enhanced disease resistance in tobacco and peanut.

We have identified a transcript derived fragment (TDF) corresponding to SGT1 in a study of differential gene expression on the resistant wild peanut, Arachis diogoi, upon challenge from the late leaf spot pathogen, Phaeoisariopsis personata, and cloned its full-length cDNA followed by subsequent validation through q-PCR. Sodium nitroprusside, salicylic acid, ethephon and methyl jasmonate induced the expression of AdSGT1, while the treatment with abscisic acid did not elicit its up-regulation. AdSGT1 is localized to both nucleus and cytoplasm. Its overexpression induced hypersensitive-like cell death in tobacco under transient conditional expression using the estradiol system, and this conditional expression of AdSGT1 was also associated with the up-regulation of NtHSR203J, HMGR and HIN1, which have been shown to be associated with hypersensitive response in tobacco in earlier studies. Expression of the cDNA in a susceptible cultivated peanut variety enhanced its resistance against the late leaf spot pathogen, Phaeoisariopsis personata, while the heterologous expression in tobacco enhanced its resistance against Phytophthora parasitica var. nicotianae, Alternaria alternata var. nicotianae and Rhizoctonia solani. Constitutive expression in peanut was associated with the co-expression of resistance-related genes, CC-NB-LRR and some protein kinases.

The wheat ethylene response factor transcription factor pathogen-induced ERF1 mediates host responses to both the necrotrophic pathogen Rhizoctonia cerealis and freezing stresses.

Sharp eyespot disease (primarily caused by the pathogen Rhizoctonia cerealis) and freezing stress are important yield limitations for the production of wheat (Triticum aestivum). Here, we report new insights into the function and underlying mechanisms of an ethylene response factor (ERF) in wheat, Pathogen-Induced ERF1 (TaPIE1), in host responses to R. cerealis and freezing stresses. TaPIE1-overexpressing transgenic wheat exhibited significantly enhanced resistance to both R. cerealis and freezing stresses, whereas TaPIE1-underexpressing wheat plants were more susceptible to both stresses relative to control plants. Following both stress treatments, electrolyte leakage and hydrogen peroxide content were significantly reduced, and both proline and soluble sugar contents were elevated in TaPIE1-overexpressing wheat, whereas these physiological traits in TaPIE1-underexpressing wheat exhibited the opposite trend. Microarray and quantitative reverse transcription-polymerase chain reaction analyses of TaPIE1-overexpressing and -underexpressing wheat plants indicated that TaPIE1 activated a subset of defense- and stress-related genes. Assays of DNA binding by electrophoretic mobility shift and transient expression in tobacco (Nicotiana tabacum) showed that the GCC boxes in the promoters of TaPIE1-activated genes were essential for transactivation by TaPIE1. The transactivation activity of TaPIE1 and the expression of TaPIE1-activated defense- and stress-related genes were significantly elevated following R. cerealis, freezing, and exogenous ethylene treatments. TaPIE1-mediated responses to R. cerealis and freezing were positively modulated by ethylene biosynthesis. These data suggest that TaPIE1 positively regulates the defense responses to R. cerealis and freezing stresses by activating defense- and stress-related genes downstream of the ethylene signaling pathway and by modulating related physiological traits in wheat.

Overexpression of cotton GhMKK4 enhances disease susceptibility and affects abscisic acid, gibberellin and hydrogen peroxide signalling in transgenic Nicotiana benthamiana.

Mitogen-activated protein kinase (MAPK) cascades are involved in plant development, stress responses and hormonal signal transduction. MAPK kinases (MAPKKs), as the key nodes in these cascades, link MAPKs and MAPKK kinases (MAPKKKs). In this study, GhMKK4, a novel group C MAPKK gene from cotton (Gossypium hirsutum), was isolated and identified. Its expression can be induced by various stresses and signalling molecules. The overexpression of GhMKK4 in Nicotiana benthamiana enhanced its susceptibility to bacterial and fungal pathogens, but had no significant effects on salt or drought tolerance. Notably, the overexpressing plants showed increased sensitivity to abscisic acid (ABA) and gibberellin A3 (GA3), and ABA and gibberellin (GA) signalling were affected on infection with Ralstonia solanacearum bacteria. Furthermore, the overexpressing plants showed more reactive oxygen species (ROS) accumulation and stronger inhibition of catalase (CAT), a ROS-scavenging enzyme, than control plants after salicylic acid (SA) treatment. Interestingly, two genes encoding ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC), the key enzymes in polyamine synthesis, exhibited reduced R. solanacearum-induced expression in overexpressing plants. These findings broaden our knowledge about the functions of MAPKKs in diverse signalling pathways and the negative regulation of disease resistance in the cotton crop.

Lactoferrin-derived resistance against plant pathogens in transgenic plants.

Lactoferrin (LF) is a ubiquitous cationic iron-binding milk glycoprotein that contributes to nutrition and exerts a broad-spectrum primary defense against bacteria, fungi, protozoa, and viruses in mammals. These qualities make lactoferrin protein and its antimicrobial motifs highly desirable candidates to be incorporated in plants to impart broad-based resistance against plant pathogens or to economically produce them in bulk quantities for pharmaceutical and nutritional purposes. This study introduced bovine LF (BLF) gene into tobacco ( Nicotiana tabacum var. Xanthi), Arabidopsis ( A. thaliana ) and wheat ( Triticum aestivum ) via Agrobacterium -mediated plant transformation. Transgenic plants or detached leaves exhibited high levels of resistance against the damping-off causing fungal pathogen Rhizoctonia solani and the head blight causing fungal pathogen Fusarium graminearum . LF also imparted resistance to tomato plants against a bacterial pathogen, Ralstonia solanacearum . Similarly, other researchers demonstrated expression of LF and LF-mediated high-quality resistance to several other aggressive fungal and bacterial plant pathogens in transgenic plants and against viral pathogens by foliar applications of LF or its derivatives. Taken together, these studies demonstrated the effectiveness of LF for improving crop quality and its biopharming potentials for pharmaceautical and nutritional applications.