Plant Defense Pathways Research Articles

Unravelling Cotton Nonexpressor of Pathogenesis-Related 1(NPR1)-Like Genes Family: Evolutionary Analysis and Putative Role in Fiber Development and Defense Pathway.

The nonexpressor of pathogenesis-related 1 (NPR1) family plays diverse roles in gene regulation in the defense and development signaling pathways in plants. Less evidence is available regarding the significance of the NPR1-like gene family in cotton (Gossypium species). Therefore, to address the importance of the cotton NPR1-like gene family in the defense pathway, four Gossypium species were studied: two tetraploid species, G. hirsutum and G. barbadense, and their two potential ancestral diploids, G. raimondii and G. arboreum. In this study, 12 NPR1-like family genes in G. hirsutum were recognized, including six genes in the A-subgenome and six genes in the D-subgenome. Based on the phylogenetic analysis, gene and protein structural features, cotton NPR-like proteins were grouped into three different clades. Our analysis suggests the significance of cis-regulatory elements in the upstream region of cotton NPR1-like genes in hormonal signaling, biotic stress conditions, and developmental processes. The quantitative expression analysis for different developmental tissues and fiber stages (0 to 25 days post-anthesis), as well as salicylic acid induction, confirmed the distinct function of different cotton NPR genes in defense and fiber development. Altogether, this study presents specifications of conservation in the cotton NPR1-like gene family and their functional divergence for development of fiber and defense properties.

Defects in the Ferroxidase That Participates in the Reductive Iron Assimilation System Results in Hypervirulence in Botrytis Cinerea.

The plant pathogen Botrytis cinerea is responsible for gray-mold disease, which infects a wide variety of species. The outcome of this host-pathogen interaction, a result of the interplay between plant defense and fungal virulence pathways, can be modulated by various environmental factors. Among these, iron availability and acquisition play a crucial role in diverse biological functions. How B. cinerea obtains iron, an essential micronutrient, during infection is unknown. We set out to determine the role of the reductive iron assimilation (RIA) system during B. cinerea infection. This system comprises the BcFET1 ferroxidase, which belongs to the multicopper oxidase (MCO) family of proteins, and the BcFTR1 membrane-bound iron permease. Gene knockout and complementation studies revealed that, compared to the wild type, the bcfet1 mutant displays delayed conidiation, iron-dependent sclerotium production, and significantly reduced whole-cell iron content. Remarkably, this mutant exhibited a hypervirulence phenotype, whereas the bcftr1 mutant presents normal virulence and unaffected whole-cell iron levels and developmental programs. Interestingly, while in iron-starved plants wild-type B. cinerea produced slightly reduced necrotic lesions, the hypervirulence phenotype of the bcfet1 mutant is no longer observed in iron-deprived plants. This suggests that B. cinerea bcfet1 knockout mutants require plant-derived iron to achieve larger necrotic lesions, whereas in planta analyses of reactive oxygen species (ROS) revealed increased ROS levels only for infections caused by the bcfet1 mutant. These results suggest that increased ROS production, under an iron sufficiency environment, at least partly underlie the observed infection phenotype in this mutant.IMPORTANCE The plant-pathogenic fungus B. cinerea causes enormous economic losses, estimated at anywhere between $10 billion and $100 billion worldwide, under both pre- and postharvest conditions. Here, we present the characterization of a loss-of-function mutant in a component involved in iron acquisition that displays hypervirulence. While in different microbial systems iron uptake mechanisms appear to be critical to achieve full pathogenic potential, we found that the absence of the ferroxidase that is part of the reductive iron assimilation system leads to hypervirulence in this fungus. This is an unusual and rather underrepresented phenotype, which can be modulated by iron levels in the plant and provides an unexpected link between iron acquisition, reactive oxygen species (ROS) production, and pathogenesis in the Botrytis-plant interaction.

Leaf metabolic profiles of two soybean genotypes differentially affect the survival and the digestibility of Anticarsia gemmatalis caterpillars

Insect pests such as Anticarsia gemmatalis cause defoliation and yield losses. Soybean breeding has obtained resistant genotypes, however the mechanism remains unknown. Studies indicated the presence of deterrents compounds in the resistant genotype IAC17, and their leaf metabolite profiles were compared to the susceptible genotype UFV105, which was elicited or not by caterpillar infestation. Cluster analysis indicated a significative distinction between these profiles as well as differences in plant defense pathways. Methylquercetins were constitutively present in the largest concentrations, specifically in the IAC17. Relationship between the resistance and the levels of phytohormones jasmonic acid, abscisic acid and salicylic acid was not observed. However, 1-aminocyclopropane -1carboxylic acid levels indicated that the ethylene may be involved in the constitutive biosynthesis of bioactive compounds. Extracts were added to the diets at three different concentrations to evaluate the effect on caterpillar survival. Lowest survival rates were observed when extracts from the resistant IAC 17 were used, at the lowest concentrations. Survival rates were not higher when IAC 17 infested by caterpillars were used. On the other hand, when extracts from the susceptible were used, the survival reductions were only observed in the highest extract concentrations. These supplementations of the diet reduced the digestive capacity, agreeing with the proteolytic activities, whereas malformations of the intestinal cells were dose dependent. The inhibitory effects persisted in higher dilutions only for the IAC17. Constitutive resistance was also explained by higher levels of protease inhibition. These results can be useful to elucidate the genes and cascades controlling the resistance.

Organic Farming Sharpens Plant Defenses in the Field.

Plants deploy a variety of chemical and physical defenses to protect themselves against herbivores and pathogens. Organic farming seeks to enhance these responses by improving soil quality, ultimately altering bottom up regulation of plant defenses. While laboratory studies suggest this approach is effective, it remains unclear whether organic agriculture encourages more-active plant defenses under real-world conditions. Working on the farms of cooperating growers, we examined gene expression in the leaves of two potato (Solanum tuberosum) varieties, grown on organic vs. conventional farms. For one variety, Norkotah, we found significantly heightened initiation of genes associated with plant-defense pathways in plants grown in organic vs. conventional fields. Organic Norkotah fields exhibited lower levels of nitrate in soil and of nitrogen in plant foliage, alongside differences in communities of soil bacteria, suggesting possible links between soil management and observed differences in plant defenses. Additionally, numbers of predatory and phloem-feeding insects were higher in organic than conventional fields. A second potato variety, Alturas, which is generally grown using fewer inputs and in poorer-quality soils, exhibited lower overall herbivore and predator numbers, few differences in soil ecology, and no differences in gene-activity in organic and conventional farming systems. Altogether, our results suggest that organic farming has the potential to increase plants' resistance to herbivores, possibly facilitating reduced need for insecticide applications. These benefits appear to be mediated by plant variety and/or farming context.

CamelliaPlant Resistance and Susceptibility to Petal Blight Disease Are Defined by the Timing of Defense Responses

The family Sclerotiniaceae includes important phytopathogens, such as Botrytis cinerea and Sclerotinia sclerotiorum, that activate plant immune responses to facilitate infection propagation. The mechanisms of plant resistance to these necrotrophic pathogens are still poorly understood. To discover mechanisms of resistance, we used the Ciborinia camelliae (Sclerotiniaceae)-Camellia spp. pathosystem. This fungus induces rapid infection of the blooms of susceptible cultivar Nicky Crisp (Camellia japonica × Camellia pitardii var. pitardii), while Camellia lutchuensis is highly resistant. Genome-wide analysis of gene expression in resistant plants revealed fast modulation of host transcriptional activity 6 h after ascospore inoculation. Ascospores induced the same defense pathways in the susceptible Camellia cultivar but much delayed and coinciding with disease development. We next tested the hypothesis that differences in defense timing influences disease outcome. We induced early defense in the susceptible cultivar using methyl jasmonate and this strongly reduced disease development. Conversely, delaying the response in the resistant species, by infecting it with actively growing fungal mycelium, increased susceptibility. The same plant defense pathways, therefore, contribute to both resistance and susceptibility, suggesting that defense timing is a critical factor in plant health, and resistance against necrotrophic pathogens may occur during the initial biotrophy-like stages.

Arbuscular mycorrhizal fungi (AMF) influences growth and insect community dynamics in Sorghum-sudangrass (Sorghum x drummondii)

Beneficial plant–microbe interactions in the rhizosphere have been found to enhance plant growth and development. Arbuscular mycorrhizal fungi (AMF), a major group among these microbes, have been found to improve plant fitness through mycorrhizal symbiosis. Despite being well documented in various natural and domesticated study systems, few studies have examined whether AMF also has cascading effects on other traits, such as influencing insect community dynamics through attraction/repulsion of beneficial and harmful insects. To test this, we planted Sorghum-sudangrass (Sorghum x drummondii), a fast-growing annual grain/forage crop, either inoculated with commercial AMF mix or left as control in lab and field experiments. We hypothesized that AMF would enhance plant growth and influence the recruitment of insect herbivores and their natural enemies due to possible alterations in plant defense pathways. Our results suggest that while AMF-inoculated plants had significantly better germination, growth, and establishment; they also experienced a lower initial incidence of Spodoptera frugiperda, a major herbivore on Sorghum in the Lower Rio Grande Valley. In addition, our insect community trapping experiment revealed that AMF-inoculated plants attracted significantly more beneficial insects (predators and parasitoids) and a lower number of damaging herbivores. Taken together, our field and lab data show that AMF can not only positively influence plant growth traits but can also provide defenses against herbivores by selectively attracting beneficial insects and repelling herbivores, with implications for sustainable pest management strategies.

Putative Role of a Yet Uncharacterized Protein Elicitor PeBb1 Derived from Beauveria bassiana ARSEF 2860 Strain against Myzus persicae (Homoptera: Aphididae) in Brassica rapa ssp. pekinensis.

This study reports the characterization of protein elicitor PeBb1 derived from entomopathogenic fungus Beauveria bassiana ARSEF-2860 strain and its putative role in induced systemic resistance in Brassica rapa ssp. pekinensis against green peach aphid Myzus persicae. The sequence of purified elicitor protein was matched with the genomic sequence of a hypothetical protein BBA_10269 from B. bassiana ARSEF-2860 (GenBank Accession No. XP_008603588.1). The protein-encoding gene PeBb1 contained 534 bp cDNA encoding a polypeptide of 177 amino acids with a molecular mass of 19 kDa. The recombinant elicitor protein was expressed in Escherichia coli using pET-28a (+) expression vector and induced necrosis in the leaves of tobacco. The effects of elicitor protein on aphid M. persicae was determined by applying three different concentrations of PeBb1 (i.e., 26, 35, 53 μM) on B. rapa plants at 4-leaf stage and the treated plants were exposed to newly emerged (0–6 h old) apterous adult aphids. Bioassay results showed significant (p < 0.05) sub-lethal effects of the exogenous application of PeBb1 elicitor on M. persicae. Moreover, the RT-qPCR gene expression analyses showed a significant up-regulation of most of the key genes linked to ethylene (ET)- and jasmonic acid (JA)-associated plant defense pathways in elicitor-treated plants. These results not only recommend the putative utilization of PeBb1 elicitor protein in future biological pest control strategies against phloem-feeding insect pests such as M. persicae, but also help in better comprehension of the mechanisms through which beneficial fungi trigger the induced plant resistance.

Unraveling the metabolite signature of citrus showing defense response towards Candidatus Liberibacter asiaticus after application of endophyte Bacillus subtilis L1-21

Huanglongbing (HLB) is one of the most serious citrus diseases, caused by phloem limited endophytic bacteria Candidatus Liberibacter asiaticus (Clas), affecting worldwide citrus production. Metabolomics approaches were employed to gain insight into mechanisms involved in defense against Clas in endophyte Bacillus subtilis L1-21 treated diseased and healthy citrus plants. Using LC-ESI-MS/MS, we compared the metabolic profile of citrus plants before and after treatment with endophyte L1-21. Our analysis indicated large differences in citrus metabolites after endophyte L1-21 application. In total, seven hundred and fourty two metabolites were detected with highest percentage recorded for organic acids, flavone, amino acid derivatives, flavone C-glycosides, nucleotide derivatives, and flavonol. Interestingly, differentially expressed metabolites (DEMs) analysis revealed the amino acids, such as lysine and tyrosine which are involved in plant defense agianst pathogen attack were regulated in diseased citrus plants after endophyte application (padj<0.05). In addition, other important metabolites up-regulated were xanthine, leucic acid, and α-Linolenic acid implicated in different plant defense pathways against Clas. Furhter, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed important pathways related to purine metabolism, biotin metabolism, and betalain biosynthesis, terpenoid-quinone biosynthesis, phenylalanine, tyrosine and lysine biosynthesis, isoflavonoid biosynthesis (padj<0.05). Taken together, this is the first study using native endophytes in diseased and healthy state of citrus which has proven to be useful in disease management by strengthening the defense of citrus to Clas pathogen.

Transcriptomic analysis reveals recovery strategies in strawberry roots after using a soil amendment in continuous cropping soil

BackgroundIn strawberry cultivation, continuous cropping (CC) obstacles seriously threaten production. A patented soil amendment (SA) can effectively relieve the CC obstacles to strawberry cultivation, but knowledge of the recovery mechanisms underlying this phenomenon is limited.ResultsIn this study, transcriptomic profiling of strawberry roots in soil with and without the SA was conducted using RNA-Seq technology to reveal gene expression changes in response to SA treatment. In total, 188 differentially expressed genes (DEGs), including 144 upregulated and 44 downregulated DEGs, were identified. SA treatment resulted in genotype-dependent responses, and the response pattern, including an overall increase in the expression of nutrient transport genes and a decrease in the expression of defense response genes, may be a possible mechanism underlying recovery strategies in strawberry roots after the application of the SA to CC soil. We also found that 9 Hsp genes involved in plant defense pathways were all downregulated in the SA-treated roots.ConclusionsThis research indicated that strawberry plants reallocated defense resources to development when SA treatment alleviated the stress caused by a CC soil environment. The present study provides an opportunity to reveal the fundamental mechanisms of the tradeoff between growth and defense in strawberry.

Host plant defense produces species-specific alterations to flight muscle protein structure and flight-related fitness traits of two armyworms.

Insects manifest phenotypic plasticity in their development and behavior in response to plant defenses, via molecular mechanisms that produce tissue-specific changes. Phenotypic changes might vary between species that differ in their preferred hosts and these effects could extend beyond larval stages. To test this, we manipulated the diet of southern armyworm (SAW; Spodoptera eridania) and fall armyworm (FAW; Spodoptera frugiperda) using a tomato mutant for jasmonic acid plant defense pathway (def1), and wild-type plants, and then quantified gene expression of Troponin t (Tnt) and flight muscle metabolism of the adult insects. Differences in Tnt spliceform ratios in insect flight muscles correlate with changes to flight muscle metabolism and flight muscle output. We found that SAW adults reared on induced def1 plants had a higher relative abundance (RA) of the A isoform of Troponin t (Tnt A) in their flight muscles; in contrast, FAW adults reared on induced def1 plants had a lower RA of Tnt A in their flight muscles compared with adults reared on def1 and controls. Although mass-adjusted flight metabolic rate showed no independent host plant effects in either species, higher flight metabolic rates in SAW correlated with increased RA of Tnt A Flight muscle metabolism also showed an interaction of host plants with Tnt A in both species, suggesting that host plants might be influencing flight muscle metabolic output by altering Tnt This study illustrates how insects respond to variation in host plant chemical defense by phenotypic modifications to their flight muscle proteins, with possible implications for dispersal.

Transcriptome Analysis Identifies Candidate Genes and Functional Pathways Controlling the Response of Two Contrasting Barley Varieties to Powdery Mildew Infection.

Powdery mildew caused by Blumeria graminis f. sp. hordei (Bgh) is one of the most serious diseases in barley. The numerous barley varieties across China provide valuable genetic resources to screen the resistant germplasm and to discover the primary genes of resistance to powdery mildew. In this study, Chinese barley variety Feng 7 was identified as a highly resistant genotype which limited Bgh colonization by cell apoptosis using leaf staining assay, while another variety Hua 30 showed high susceptibility. The performance of high resistance to Bgh in F1 plants from the two varieties suggested dominant gene(s) controlled the resistance to powdery mildew in Feng 7. To understand the host transcriptional response to Bgh infection, these two barley varieties Feng 7 and Hua 30 were inoculated with Bgh, and their transcriptional profiling using RNA sequencing (RNA-seq) at four time points (12 h post-inoculation (hpi), 24 hpi, 48 hpi, and 72 hpi) were compared. 4318 differentially expressed genes (DEGs), including 2244 upregulated and 2074 downregulated genes, were detected in Feng 7, compared with Hua 30 at 12 hpi. 4907 DEGs (2488 upregulated and 2419 downregulated) were detected at 24 hpi. 4758 DEGs (2295 upregulated and 2463 downregulated) were detected at 48 hpi. 3817 DEGs (2036 upregulated and 1781 downregulated) were detected at 72 hpi. The results showed the number of DEGs between two varieties peaked at 24 hpi (for the upregulated) or 48 hpi (for the downregulated), which is matched with the processing of Bgh infection. In addition, the number of upregulated DEGs involved in the functional pathways of plant defense (mitogen-activated protein kinase (MAPK) pathway and plant hormone signal transduction) is elevated remarkably at 24 hpi. Six candidate genes (PR13, glutaredoxin, alcohol dehydrogenase, and cytochrome P450) were identified in Feng 7. All of them present continuous expression at higher levels upon Bgh infection, compared with the performance in Hua 30, which revealed the potential contribution to Feng 7 mediate resistance to Bgh. In conclusion, the candidate genes and relevant pathways provided key information towards understanding the defense of barley to Bgh attack and the molecular mechanisms of different genetic resistance to powdery mildew.

Disruption of Arabidopsis neutral ceramidases 1 and 2 results in specific sphingolipid imbalances triggering different phytohormone-dependent plant cell death programmes.

Sphingolipids act as regulators of programmed cell death (PCD) and the plant defence response. The homeostasis between long-chain base (LCB) and ceramide (Cer) seems to play an important role in executions of PCD. Therefore, deciphering the role of neutral ceramidases (NCER) is crucial to identify the sphingolipid compounds that trigger and execute PCD. We performed comprehensive sphingolipid and phytohormone analyses of Arabidopsis ncer mutants, combined with gene expression profiling and microscopic analyses. While ncer1 exhibited early leaf senescence (developmentally controlled PCD - dPCD) and an increase in hydroxyceramides, ncer2 showed spontaneous cell death (pathogen-triggered PCD-like - pPCD) accompanied by an increase in LCB t18:0 at 35d, respectively. Loss of NCER1 function resulted in accumulation of jasmonoyl-isoleucine (JA-Ile) in the leaves, whereas disruption of NCER2 was accompanied by higher levels of salicylic acid (SA) and increased sensitivity to Fumonisin B1 (FB1 ). All mutants were also found to activate plant defence pathways. These data strongly suggest that NCER1 hydrolyses ceramides whereas NCER2 functions as a ceramide synthase. Our results reveal an important role of NCER in the regulation of both dPCD and pPCD via a tight connection between the phytohormone and sphingolipid levels in these two processes.

Variation in both host defense and prior herbivory can alter plant-vector-virus interactions

BackgroundWhile virus-vector-host interactions have been a major focus of both basic and applied ecological research, little is known about how different levels of plant defense interact with prior herbivory to affect these relationships. We used genetically-modified strains of tomato (Solanum lycopersicum) varying in the jasmonic acid (JA) plant defense pathways to explore how plant defense and prior herbivory affects a plant virus (tomato yellow leaf curl virus, ‘TYLCV’), its vector (the whitefly Bemisia tabaci MED), and the host.ResultsVirus-free MED preferred low-JA over high-JA plants and had lower fitness on high-JA plants. Viruliferous MED preferred low-JA plants but their survival was unaffected by JA levels. While virus-free MED did not lower plant JA levels, viruliferous MED decreased both JA levels and the expression of JA-related genes. Infestation by viruliferous MED reduced plant JA levels. In preference tests, neither virus-free nor viruliferous MED discriminated among JA-varying plants previously exposed to virus-free MED. However, both virus-free and viruliferous MED preferred low-JA plant genotypes when choosing between plants that had both been previously exposed to viruliferous MED. The enhanced preference for low-JA genotypes appears linked to the volatile compound neophytadiene, which was found only in whitefly-infested plants and at concentrations inversely related to plant JA levels.ConclusionsOur findings illustrate how plant defense can interact with prior herbivory to affect both a plant virus and its whitefly vector, and confirm the induction of neophytadiene by MED. The apparent attraction of MED to neophytadiene may prove useful in pest detection and management.

The Ecology of Salicylic Acid Signaling: Primary, Secondary and Tertiary Effects with Applications in Agriculture.

The salicylic acid pathway is one of the primary plant defense pathways, is ubiquitous in vascular plants, and plays a role in rapid adaptions to dynamic abiotic and biotic stress. Its prominence and ubiquity make it uniquely suited for understanding how biochemistry within plants can mediate ecological consequences. Induction of the salicylic acid pathway has primary effects on the plant in which it is induced resulting in genetic, metabolomic, and physiologic changes as the plant adapts to challenges. These primary effects can in turn have secondary consequences for herbivores and pathogens attacking the plant. These secondary effects can both directly influence plant attackers and mediate indirect interactions between herbivores and pathogens. Additionally, stimulation of salicylic acid related defenses can affect natural enemies, predators and parasitoids, which can recruit to plant signals with consequences for herbivore populations and plant herbivory aboveground and belowground. These primary, secondary, and tertiary ecological consequences of salicylic acid signaling hold great promise for application in agricultural systems in developing sustainable high-yielding management practices that adapt to changing abiotic and biotic environments.

Comparative Studies on Gene Expression of Rice and Wheat in Response to Fungal Infection

Cereals are the foremost necessary foods for growing population of human. Wheat (Triticum aestivum) is the first important and strategic cereal crop for the majority of world’s populations. It is the most necessary staple food. Although rice (oryzae sativa) has the second place because of planted area but it serves as the most important food source for Asian countries. Wheat and rice production may be severely restricted by biotic and abiotic constraints. Disease is the major biotic stress in several regions.Comparative sequence analysis is a powerful tool to study homologous gene families, define conserved gene functions between orthologs, and identify lineage- and species-specific genes. Most annotations of newly sequenced genomes are based on similarity with sequences for which functional information is available. Apart from conserved sequences, inter-species differences provide important clues about evolutionary history and species-specific adaptations. In our study, two RNA-sequencing data sets of resistant variety of wheat (Triticum aestivum L.,) after infection with leaf rust fungus, Puccinia triticina and resistant variety of rice (Oryza sativa L.,) after infection with blast fungus, Magnaporthe oryzae were compared. 31768 up-regulated genes in wheat and 3902 up-regulated genes in rice were filtered according to fold change more than 3 and removing variants, 250 upregulated genes of wheat and rice were aligned and phylogenetic tree was generated. The result of phylogenetic tree showed close relationship between ten aligned gene pairs of wheat and rice. Two pairs of aligned gene pairs were selected randomly, super family of these pairs were obtained, the result showed that each aligned pair of proteins shared the same protein family and the same annotation and all pairs participate in plant defense pathways. Then, the gene expression of the two pairs were validated by Real-time PCR after infecting wheat with Puccinia triticina and rice with Magnaporthe grisea. Each aligned pair of the two pairs shared the same manner of expression with few exceptions in rice.

Small RNA profiling of Cavendish banana roots inoculated with Fusarium oxysporum f. sp. cubense race 1 and tropical race 4

Fusarium wilt, caused by the soil-borne fungal pathogen, Fusarium oxysporum f. sp. cubense (Foc), is considered as one of the most threatening diseases of banana. The Cavendish variety, resistant to Foc race 1 (R1), is susceptible to tropical race 4 (TR4), an aggressive race of the pathogen which is of increasing concern worldwide. Previous studies have revealed that plant small RNAs (sRNAs) play crucial roles in the host response to pathogen infection. To investigate the roles of sRNAs involved in the interaction of the banana-Foc pathosystem, small RNA profiles of Cavendish banana roots inoculated with Foc TR4 and Foc R1 were obtained and analyzed in the present study using Next-Generation Sequencing (NGS) technology. A total of 112 discrete mature microRNAs (miRNAs) belonging to 22 known miRNA families were found across all constructed sRNA libraries. The expression of miR166, miR159 and miR156 was up-regulated in TR4-inoculated samples as compared to mock-inoculated samples, while the expression of these miRNAs was approximately the same in R1-inoculated and mock-inoculated samples. Consistent with the sequencing data, qRT-PCR results demonstrated up-regulation of these miRNAs and down-regulation of their target genes in TR4-inoculated samples, but not in R1-inoculated samples. Considering Cavendish banana is resistant to R1 and susceptible to TR4, it is possible that these sRNAs and their target genes are involved in particular plant defence pathways such as salicylic acid-based defence. The findings will pave way for future investigations of the defence mechanism and potential approaches of resistance improvement.

A genome‐wide association study for partial resistance to southern corn rust in tropical maize

AbstractSouthern corn rust (SCR) is a fungal disease found on corn in several countries worldwide. In Brazil, the disease can result in productivity losses of 65%, especially in areas with a history of the disease. In this study, the genetic architecture and identification of genomic regions associated with SCR resistance was investigated by performing a genome‐wide association study. Genotyping‐by‐sequencing was performed to carry out the association between single nucleotide polymorphism (SNP) markers and phenotypic data from two environments on a panel of 164 maize inbred lines. Eight SNPs were identified as significant for SCR resistance. These SNPs were colocalized with QTL regions, some of which underlie candidate resistance genes with functions that play an important role in the stress response during pathogen recognition. These candidate genes, involved in plant defense pathways, could be associated with partial resistance to SCR and provide a partial comprehensive insight into the genetic architecture of this trait. After validation of the SNPs, they will be useful for marker–assisted selection and for a better understanding of maize resistance to SCR.

Rice susceptibility to root-knot nematodes is enhanced by the Meloidogyne incognita MSP18 effector gene.

This study revealed novel insights into the function of MSP18 effector during root-knot nematode parasitism in rice roots. MSP18 may modulate host immunity and enhance plant susceptibility to Meloidogyne spp. Rice (Oryza sativa) production is seriously impacted by root-knot nematodes (RKN), including Meloidogyne graminicola, Meloidogyne incognita, and Meloidogyne javanica, in upland and irrigated culture systems. Successful plant infection by RKN is likely achieved by releasing into the host cells some effector proteins to suppress the activation of immune responses. Here, we conducted a series of functional analyses to assess the role of the Meloidogyne-secreted protein (MSP) 18 from M. incognita (Mi-MSP18) during rice infection by RKN. Developmental expression profiles of M. javanica and M. graminicola showed that the MSP18 gene is up-regulated throughout nematode parasitic stages in rice. Reproduction of M. javanica and M. graminicola is enhanced in rice plants overexpressing Mi-MSP18, indicating that the Mi-MSP18 protein facilitates RKN parasitism. Transient expression assays in onion cells suggested that Mi-MSP18 is localized to the cytoplasm of the host cells. In tobacco, Mi-MSP18 suppressed the cell death induced by the INF1 elicitin, suggesting that Mi-MSP18 can interfere with the plant defense pathways. The data obtained in this study highlight Mi-MSP18 as a novel RKN effector able to enhance plant susceptibility and modulate host immunity.

Effect of polyamines and nitric oxide in Piriformospora indica-induced resistance and basal immunity of wheat against Fusarium pseudograminearum

Fusarium crown rot of wheat is an important disease worldwide. The lack of commercial resistant cultivars and effective fungicides against Fusarium, make controlling the disease very difficult. Biocontrol can be an environmentally friendly method to reduce the progress of various diseases caused by Fusarium species. Piriformospora indica is a root endophytic fungus with a wide range of host plants, which increases their growth and tolerance to biotic and abiotic stresses. In this study, capability of P. indica to protect wheat seedlings against Fusarium pseudograminearum, causing crown rot, was investigated and the role of polyamines (PAs) and nitric oxide (NO) as signal molecules involved in plant defense pathways in induced resistance by this endophytic fungus was evaluated in this pathosystem for the first time. Our results showed that P. indica did not have any antagonistic effect on F. pseudograminearum in vitro but considerably reduced the disease progress on wheat seedlings and detached leaves. Also, P. indica increased plant growth parameters compared to the controls in greenhouse. Application of spermidine (Spd; a polyamine) and sodium nitroprusside (SNP; a NO donor) revealed that PAs and NO had significant effect on basal immunity and P. indica-induced resistance (Pi-IR) via elevation of H2O2 levels, guaiacol peroxidase (GPX) and catalase (CAT) activity, callose deposition, relative water content (RWC) and membrane stability index (MSI) compared to the plants only inoculated with F. pseudograminearum and uninoculated controls. In addition, our data demonstrated that PAs and NO synergistically enhanced basal resistance and Pi-IR against Fusarium crown rot in wheat plants.

Transcriptomic and proteomic response of Manihot esculenta to Tetranychus urticae infestation at different densities.

Tetranychus urticae (Acari: Tetranychidae) is an extremely serious cassava (Manihot esculenta) pest. Building a genomic resource to investigate the molecular mechanisms of cassava responses to T. urticae is vital for characterizing cassava resistance to mites. Based on the tolerance of cassava varieties to mite infestation (focusing on mite development rate, fecundity and physiology), cassava variety SC8 was selected to analyze transcriptomic and proteomic changes after 5days of T. urticae feeding. Transcriptomic analysis revealed 698 and 2140 genes with significant expression changes under low and high mite infestation, respectively. More defense-related genes were found in the enrichment pathways at high mite density than at low density. In addition, iTRAQ-labeled proteomic analysis revealed 191 proteins with significant expression changes under low mite infestation. Differentially expressed genes and proteins were mainly found in the following defense-related pathways: flavonoid biosynthesis, phenylpropanoid biosynthesis, and glutathione metabolism under low-density mite feeding and plant hormone signal transduction and plant-pathogen interaction pathways under high-density mite feeding. The plant hormone signal transduction network, involving ethylene, jasmonic acid, and salicylic acid transduction pathways, was explored in relation to the M. esculenta response to T. urticae. Correlation analysis of the transcriptome and proteome generated a Pearson correlation coefficients of R = 0.2953 (P < 0.01), which might have been due to post-transcriptional or post-translational regulation resulting in many genes being inconsistently expressed at both the transcript and protein levels. In summary, the M. esculenta transcriptome and proteome changed in response to T. urticae, providing insight into the general activation of plant defense pathways in response to mite infestation.