Graminicola Infection Research Articles

A maize enzyme from the 2-oxoglutarate-dependent oxygenase family with unique kinetic properties, mediates resistance against pathogens and regulates senescence.

In plants, salicylic acid (SA) hydroxylation regulates SA homoeostasis, playing an essential role during plant development and response to pathogens. This reaction is catalysed by SA hydroxylase enzymes, which hydroxylate SA producing 2,3-dihydroxybenzoic acid (2,3-DHBA) and/or 2,5-dihydroxybenzoic acid (2,5-DHBA). Several SA hydroxylases have recently been identified and characterised from different plant species, but no such activity has yet been reported in maize. In this work, we describe the identification and characterisation of a new SA hydroxylase in maize plants. This enzyme, with high sequence similarity to previously described SA hydroxylases from Arabidopsis and rice, converts SA into 2,5-DHBA; however, it has different kinetic properties to those of previously characterised enzymes, and it also catalysers the conversion of the flavonoid dihydroquercetin into quercetin in in vitro activity assays, suggesting that the maize enzyme may have different roles in vivo to those previously reported from other species. Despite this, ZmS5H can complement the pathogen resistance and the early senescence phenotypes of Arabidopsis s3h mutant plants. Finally, we characterised a maize mutant in the S5H gene (s5hMu) that has altered growth, senescence and increased resistance against Colletotrichum graminicola infection, showing not only alterations in SA and 2,5-DHBA but also in flavonol levels. Together, the results presented here provide evidence that SA hydroxylases in different plant species have evolved to show differences in catalytic properties that may be important to fine tune SA levels and other phenolic compounds such as flavonols, to regulate different aspects of plant development and pathogen defence.

Plant immunity suppression by an β-1,3-glucanase of the maize anthracnose pathogen Colletotrichum graminicola

BackgroundMany phytopathogens secrete a large number of cell wall degrading enzymes (CWDEs) to decompose host cell walls in order to penetrate the host, obtain nutrients and accelerate colonization. There is a wide variety of CWDEs produced by plant pathogens, including glycoside hydrolases (GHs), which determine the virulence, pathogenicity, and host specificity of phytopathogens. The specific molecular mechanisms by which pathogens suppress host immunity remain obscure.ResultIn this study, we found that CgEC124 encodes a glycosyl hydrolase with a signal peptide and a conserved Glyco_hydro_cc domain which belongs to glycoside hydrolase 128 family. The expression of CgEC124 was significantly induced in the early stage of Colletotrichum graminicola infection, especially at 12 hpi. Furthermore, CgEC124 positively regulated the pathogenicity, but it did not impact the vegetative growth of mycelia. Ecotopic transient expression of CgEC124 decreased the disease resistance and callose deposition in maize. Moreover, CgEC124 exhibited the β-1,3-glucanase activity and suppresses glucan-induced ROS burst in maize leaves.ConclusionsOur results indicate that CgEC124 is required for full virulence of C. graminicola but not for vegetative growth. CgEC124 increases maize susceptibility by inhibiting host reactive oxygen species burst as well as callose deposition. Meanwhile, our data suggests that CgEC124 explores its β-1,3-glucanase activity to prevent induction of host defenses.

Brown planthopper infestation on rice reduces plant susceptibility to Meloidogyne graminicola by reducing root sugar allocation.

Plants are simultaneously attacked by different pests that rely on sugars uptake from plants. An understanding of the role of plant sugar allocation in these multipartite interactions is limited. Here, we characterized the expression patterns of sucrose transporter genes and evaluated the impact of targeted transporter gene mutants and brown planthopper (BPH) phloem-feeding and oviposition on root sugar allocation and BPH-reduced rice susceptibility to Meloidogyne graminicola. We found that the sugar transporter genes OsSUT1 and OsSUT2 are induced at BPH oviposition sites. OsSUT2 mutants showed a higher resistance to gravid BPH than to nymph BPH, and this was correlated with callose deposition, as reflected in a different effect on M. graminicola infection. BPH phloem-feeding caused inhibition of callose deposition that was counteracted by BPH oviposition. Meanwhile, this pivotal role of sugar allocation in BPH-reduced rice susceptibility to M. graminicola was validated on rice cultivar RHT harbouring BPH resistance genes Bph3 and Bph17. In conclusion, we demonstrated that rice susceptibility to M. graminicola is regulated by BPH phloem-feeding and oviposition on rice through differences in plant sugar allocation.

Underlying Mechanisms of the Hedgehog-Like Panicle and Filamentous Leaf Tissue Symptoms Caused by Sclerospora graminicola in Foxtail Millet.

Downy mildew caused by Sclerospora graminicola is a systemic infectious disease affecting foxtail millet production in Africa and Asia. S. graminicola-infected leaves could be decomposed to a state where only the veins remain, resulting in a filamentous leaf tissue symptom. The aim of the present study was to investigate how S. graminicola influences the formation of the filamentous leaf tissue symptoms in hosts at the morphological and molecular levels. We discovered that vegetative hyphae expanded rapidly, with high biomass accumulated at the early stages of S. graminicola infection. In addition, S. graminicola could affect spikelet morphological development at the panicle branch differentiation stage to the pistil and stamen differentiation stage by interfering with hormones and nutrient metabolism in the host, resulting in hedgehog-like panicle symptoms. S. graminicola could acquire high amounts of nutrients from host tissues through secretion of β-glucosidase, endoglucanase, and pectic enzyme, and destroyed host mesophyll cells by mechanical pressure caused by rapid expansion of hyphae. At the later stages, S. graminicola could rapidly complete sexual reproduction through tryptophan, fatty acid, starch, and sucrose metabolism and subsequently produce numerous oospores. Oospore proliferation and development further damage host leaves via mechanical pressure, resulting in a large number of degraded and extinct mesophyll cells and, subsequently, malformed leaves with only veins left, that is, "filamentous leaf tissue." Our study revealed the S. graminicola expansion characteristics from its asexual to sexual development stages, and the potential mechanisms via which the destructive effects of S. graminicola on hosts occur at different growth stages.

Transcriptome analysis of foxtail millet inflorescence tissue in response to Sclerospora graminicola infection

Floral reversion caused by Sclerospora graminicola infection seriously affects development and grain formation of floral organs in foxtail millet. Herein, we observed morphological changes to infected panicles from stamen and pistil differentiation to flowering stages, and used RNA sequencing and weighted correlation network analysis (WGCNA) to analyse the key genes and pathways involved in interactions between foxtail millet and S. graminicola. All floral organs of infected panicles, including glume, lemma and palea, transformed into leaf-like structures, leading to malformed inflorescence. Transcriptome analysis showed that S. graminicola infection regulated host physiology and hormone metabolism, and differentially expressed genes (DEGs) were mainly enriched in disease resistance responses involving plant hormone metabolism, peroxidase activity and flavonoid biosynthesis pathways. Subsequently, 8 % of identified DEGs were predicted to be transcription factors, including bHLH and WRKY members related to biotic stress. Plant physiological measurements showed that infection and stress caused by S. graminicola led to changes in antioxidant enzymes superoxide dismutase and peroxidase, and defence hormones jasmonic acid, salicylic acid and 1-aminocyclopropane-1-carboxylic acid in foxtail millet. WGCNA identified 17 hub genes in four key modules (black, magenta, green and turquoise) including a MYB domain protein (Si2g07390), an ethylene-responsive transcription factor ERF094 (Si8g10010) and an NAC domain protein (Si5g40460). The results indicate that transcriptional expression, hormones and oxidation-reduction participate in inflorescence reversion in foxtail millet caused by S. graminicola.

First Report of Colletotrichum graminicola Causing Maize Anthracnose in Galicia, Northwestern Spain.

Maize (Zea mays) is one of the most important crops worldwide, and fungal diseases are responsible for major losses in food production. Anthracnose caused by Colletotrichum graminicola can infect all maize tissues, although stalk rot and seedling blight cause more significant economic damage (Munkvold and White, 2016). Anthracnose stalk rot is characterized by a distinctive external blackening of the lower stalks resulting in large black streaks, while the pith turns dark brown and has a shredded appearance. Like most stalk rots, the most obvious symptom is a sudden death of plants before grain maturity, and plant lodging. Symptoms commonly appear late in the season, suspicious maize stems of cultivar Tuy exhibiting symptoms of anthracnose stalk rot were collected from a field in Pontevedra, Galicia, Spain (Geographical coordinates: 42°23'27.1" N - 8°30'46.3" W) between June and December of 2022. Stem samples, approximately 50 mm2, were dissected and surface-disinfected for 90 seconds in 20% sodium hypochlorite (v/v) and rinsed three times in sterile distilled water. The samples were transferred to one half-strength acidified potato dextrose agar (PDA) supplemented with ampicillin (100 µg/mL) and lactic acid 90% (1.5 mL/L) and incubated for 5 days at 25 ºC (Sukno et al. 2008). Single spores were transferred to fresh PDA plates to obtain pure culture isolates. A total of six isolates were obtained, and among them, two were selected for further characterization (SP-36820-1 and SP-36820-3). Colonies grown on PDA have dark gray aerial mycelium with orange-colored spore masses. Conidia are falcate, slightly curved, tapered toward the tips, and are produced in acervuli with setae, measuring 37.65 to 24.84 x 8.02 to 4.67 µm, respectively (n = 100). These morphological characteristics are in agreement with C. graminicola previously described by Bergstrom and Nicholson (1999). Isolates were grown in potato dextrose broth (PDB) for 3 days at 25 ºC and total genomic DNA was extracted using a DNeasy Plant Mini Kit (Qiagen Inc., Valencia, CA, USA). The internal transcribed spacer region of rDNA and the manganese-type superoxide dismutase gene (SOD2) were amplified using primers ITS4/ITS5 (White et al. 1990) and SOD625/SOD507 (Fang et al. 2002) and consequently sequenced. GenBank BLAST analysis revealed that the sequences were 100% identical to strains of C. graminicola. All sequences were deposited in GenBank (see e-Xtra 1 for accession numbers). To confirm Koch's postulates, plants of a derivative of maize inbred line Mo940 (developmental stage V3) were placed horizontally in a tray for inoculation and 20 droplets (7.5 µL) of a suspension of 3 x 105 conidia per milliliter were placed on the surface of the third leaf. The trays were closed to retain moisture and incubated overnight at 23ºC. The next day, the plants were returned to a vertical position and incubated in a growth chamber at 25ºC with 80% humidity and a light cycle of 16 h of light and 8 h of dark (Vargas et al. 2012). After four days inoculated leaves presented brown elongated lesions with necrotic centers consistent with C. graminicola infection, whereas control plants remained asymptomatic. The strains reisolated from infected leaves were morphologically identical to the original isolates. To our knowledge, this is the first report of Colletotrichum graminicola causing maize anthracnose in Spain. Recently, maize anthracnose was also reported in Bosnia and Herzegovina and China (Duan et al. 2019; Cuevas-Fernández et al. 2019), suggesting the pathogen's geographic range is increasing, which may be a threat to maize cultivation in locations with optimal humid conditions for disease development.

Integrated transcriptome and metabolome analysis revealed that flavonoids enhanced the resistance of Oryza sativa against Meloidogyne graminicola.

Rice is a crucial food crop worldwide, but its yield and quality are significantly affected by Meloidogyne graminicola is a root knot nematode. No rice variety is entirely immune to this nematode disease in agricultural production. Thus, the fundamental strategy to combat this disease is to utilize rice resistance genes. In this study, we conducted transcriptome and metabolome analyses on two rice varieties, ZH11 and IR64. The results indicated that ZH11 showed stronger resistance than IR64. Transcriptome analysis revealed that the change in gene expression in ZH11 was more substantial than that in IR64 after M. graminicola infection. Moreover, GO and KEGG enrichment analysis of the upregulated genes in ZH11 showed that they were primarily associated with rice cell wall construction, carbohydrate metabolism, and secondary metabolism relating to disease resistance, which effectively enhanced the resistance of ZH11. However, in rice IR64, the number of genes enriched in disease resistance pathways was significantly lower than that in ZH11, which further explained susceptibility to IR64. Metabolome analysis revealed that the metabolites detected in ZH11 were enriched in flavonoid metabolism and the pentose phosphate pathway, compared to IR64, after M. graminicola infection. The comprehensive analysis of transcriptome and metabolome data indicated that flavonoid metabolism plays a crucial role in rice resistance to M. graminicola infection. The content of kaempferin, apigenin, and quercetin in ZH11 significantly increased after M. graminicola infection, and the expression of genes involved in the synthetic pathway of flavonoids also significantly increased in ZH11. Our study provides theoretical guidance for the precise analysis of rice resistance and disease resistance breeding in further research.

Comparative transcriptome profiling of resistant and susceptible foxtail millet responses to Sclerospora graminicola infection

BackgroundDowny mildew of foxtail millet, which is caused by the biotrophic oomycete Sclerospora graminicola (Sacc.) Schroeter, is one of the most disruptive diseases. The foxtail millet-S. graminicola interaction is largely unexplored. Transcriptome sequencing technology can help to reveal the interaction mechanism between foxtail millet and its pathogens.ResultsTransmission electron microscopy observations of leaves infected with S. graminicola showed that the structures of organelles in the host cells gradually became deformed and damaged, or even disappeared from the 3- to 7-leaf stages. However, organelles in the leaves of resistant variety were rarely damaged. Moreover, the activities of seven cell wall degrading enzymes in resistant and susceptible varieties were also quite different after pathogen induction and most of enzymes activities were significantly higher in the susceptible variety JG21 than in the resistant variety G1 at all stages. Subsequently, we compared the transcriptional profiles between the G1 and JG21 in response to S. graminicola infection at 3-, 5-, and 7-leaf stages using RNA-Seq technology. A total of 473 and 1433 differentially expressed genes (DEGs) were identified in the resistant and susceptible varieties, respectively. The pathway analysis of the DEGs showed that the highly enriched categories were related to glutathione metabolism, plant hormone signalling, phenylalanine metabolism, and cutin, suberin and wax biosynthesis. Some defence-related genes were also revealed in the DEGs, including leucine-rich protein kinase, Ser/Thr protein kinase, peroxidase, cell wall degrading enzymes, laccases and auxin response genes. Our results also confirmed the linkage of transcriptomic data with qRT-PCR data. In particular, LRR protein kinase encoded by Seita.8G131800, Ser/Thr protein kinase encoded by Seita.2G024900 and Seita. 2G024800, which have played an essential resistant role during the infection by S. graminicola.ConclusionsTranscriptome sequencing revealed that host resistance to S. graminicola was likely due to the activation of defence-related genes, such as leucine-rich protein kinase and Ser/Thr protein kinase. Our study identified pathways and genes that contribute to the understanding of the interaction between foxtail millet and S. graminicola at the transcriptomic level. The results will help us better understand the resistance mechanism of foxtail millet against S. graminicola.

CRISPR/Cas9-targeted mutagenesis of a representative member of a novel PR10/Bet v1-like protein subfamily significantly reduces rice plant height and defense against Meloidogyne graminicola

Plant PR10/Bet v1-like proteins are involved in defense against microbial pathogens, however, whether they participate in host defense against plant-parasitic animals including nematodes remains unknown. Here, according to the phylogeny, sequence-similarity, and secondary structure analyses, we found that the rice OsBet v1 protein and its homologs constitute a new subfamily of PR10/Bet v1-like protein. Reverse transcription-quantitative PCR assay showed that OsBet v1 was highly expressed in rice roots and induced by Meloidogyne graminicola infection. Using a transient expression assay in rice protoplasts, we demonstrated that OsBet v1 was localized in the cytoplasm and nucleus. Furthermore, CRISPR/Cas9-targeted mutagenesis of OsBet v1 significantly increased rice susceptibility to M. graminicola, but reduced rice plant height. In addition, the expression levels of two peroxidase genes (peroxidase 5 and peroxidase 56) were significantly down-regulated in OsBet v1 knockout mutants compared with those in wild-type rice plants. Taken together, this study identified a new PR10/Bet v1-like protein subfamily in plant and revealed the involvement of OsBet v1, a representative member of the subfamily, in rice growth and defense against M. graminicola. This provides a new insight into the role of plant PR10/Bet v1-like proteins in plant–nematode interactions.

Molecular Genetics of Anthracnose Resistance in Maize.

Maize (Zea mays), also called corn, is one of the top three staple food crops worldwide and is also utilized as feed (e.g., feed grain and silage) and a source of biofuel (e.g., bioethanol). Maize production is hampered by a myriad of factors, including although not limited to fungal diseases, which reduce grain yield and downgrade kernel quality. One such disease is anthracnose leaf blight and stalk rot (ALB and ASR) caused by the hemibiotrophic fungal pathogen Colletotrichum graminicola. The pathogen deploys a biphasic infection strategy to colonize susceptible maize genotypes, comprising latent (symptomless) biotrophic and destructive (symptomatic) necrotrophic phases. However, the resistant maize genotypes restrict the C. graminicola infection and in planta fungal proliferation during the biotrophic phase of the infection. Some studies on the inheritance of ASR resistance in the populations derived from biparental resistant and susceptible genotypes reveal that anthracnose is likely a gene-for-gene disease in which the resistant maize genotypes and C. graminicola recognize each other by their matching pairs of nucleotide-binding leucine-rich repeat resistance (NLR) proteins (whose coding genes are localized in disease QTL) and effectors (1–2 effectors/NLR) during the biotrophic phase of infection. The Z. mays genome encodes approximately 144 NLRs, two of which, RCg1 and RCg1b, located on chromosome 4, were cloned and functionally validated for their role in ASR resistance. Here, we discuss the genetic architecture of anthracnose resistance in the resistant maize genotypes, i.e., disease QTL and underlying resistance genes. In addition, this review also highlights the disease cycle of C. graminicola and molecular factors (e.g., virulence/pathogenicity factors such as effectors and secondary metabolites) that contribute to the pathogen’s virulence on maize. A detailed understanding of molecular genetics underlying the maize—C. graminicola interaction will help devise effective management strategies against ALB and ASR.

Meloidogyne graminicola’s Effect on Growth Performance of Rice under Low Population Density

Meloidogyne graminicola is a destructive soil-borne pathogen that causes rice yield losses (Oryza sativa L.) in tropical and subtropical areas. This study investigated the effect of M. graminicola population densities on plant height, heading, and the photosynthetic parameters of rice in a greenhouse. Two-week-old rice plants were inoculated with different M. graminicola densities (250, 500, 750, 1000, 1500, and 2000 J2s/plant) and observations were recorded at 30, 60, and 90 days after inoculation (DAI). Reductions in growth and photosynthetic parameters caused by M. graminicola densities were calculated in relation to a control (non-inoculated rice). Results revealed that M. graminicola infection with low population densities (0–500 J2s/plant) did not influence the rice plant height during 30–60 DAI, but significantly lowered the plant height, panicle growth rate, and panicle length of rice at 90 DAI. The chlorophyll content of rice inoculated with 500–2000 J2s was significantly lower than that of the control. Furthermore, M. graminicola infection with 500 J2s/plant significantly lowered the transpiration rate and net photosynthetic rate by 21.21% and 21.81%, respectively, compared with the control (p < 0.05). M. graminicola with a low population density significantly reduced the net photosynthetic rate of rice, which affected organic matter accumulation, resulting in growth retardation and lower yields (p < 0.05).

Impact of Sclerospora graminicola infection on physiological mechanisms and hormonal regulation of floral reversion in pearl millet [Pennisetum glaucum (L.) R. Br

The present study was undertaken to assess the impact of Sclerospora graminicola infection on the physiological and developmental changes in pearl millet. Disease progression of biotrophic pathogen Sclerospora graminicola causing downy mildew was determined to alter the anatomical, biochemical and photosynthetic characteristics of the flag leaf. The defense mechanism was initiated by the host plant in response to S. graminicola infection. The plugging of stomatal pores and vascular bundles with an increase in trichome density was observed post infection. The infection caused an increase in internal CO2 concentration, decrease in net photosynthetic rate, stomatal conductance and transpiration rate of the flag leaf. The disease infection reduced the total soluble sugar content of the host plant, whereas increased the starch and the total phenolic content. The increase in starch content in the downy mildew infected leaves might have imparted feedback inhibition leading to reduced photosynthetic activity. The leaf malondialdehyde (MDA) content and enzymatic antioxidants viz. peroxidase, polyphenol oxidase and indole-3-acetic acid (IAA) oxidase increased post infection. Hence, this imbalance in flag leaf metabolic activity affected the developing panicle and induced developmental alterations which redirected floral development and fate of the meristem. An increase in tiller number was possibly due to the release of apical dominance caused by fungal infection which regulated the endogenous auxin content to a three fold increase. Floral reversion due to the pathogen infection suggests that there was transport of auxin from the developing axillary buds that might have led to malformed ear proliferation. The information on carbon assimilation and hormone imbalance causing floral reversion in pearl millet by downy mildew pathogen can aid in management practices aimed at reducing the disease impact on the crop.

Physiological and biophysical alterations in maize plants caused by Colletotrichum graminicola infection verified by OJIP study

Physiological and biophysical alterations in maize plants caused by Colletotrichum graminicola infection verified by OJIP study

Molecular Characterization of the Purine Degradation Pathway Genes ALA1 and URE1 of the Maize Anthracnose Fungus Colletotrichum graminicola Identified Urease as a Novel Target for Plant Disease Control.

Fungal pathogenicity is governed by environmental factors, with nitrogen playing a key role in triggering pathogenic development. Spores germinating on the plant cuticle are exposed to a nitrogen-free environment, and reprograming of nitrogen metabolism is required for bridging the time needed to gain access to the nitrogen sources of the host. Although degradation of endogenous purine bases efficiently generates ammonium and may allow the fungus to bridge the preinvasion nitrogen gap, the roles of the purine degradation pathway and of the key genes encoding allantoicase and urease are largely unknown in plant pathogenic fungi. To investigate the roles of the allantoicase and urease genes ALA1 and URE1 of the maize anthracnose fungus Colletotrichum graminicola in pathogenic development, we generated ALA1:eGFP and URE1:eGFP fusion strains as well as allantoicase- and urease-deficient mutants. Virulence assays, live cell, and differential interference contrast imaging, chemical complementation and employment of a urease inhibitor showed that the purine degradation genes ALA1 and URE1 are required for bridging nitrogen deficiency at early phases of the infection process and for full virulence. Application of the urease inhibitor acetohydroxamic acid did not only protect maize from C. graminicola infection, but also interfered with the infection process of the wheat powdery mildew fungus Blumeria graminis f. sp. tritici, the maize and broad bean rusts Puccinia sorghi and Uromyces viciae-fabae, and the potato late blight pathogen Phytophthora infestans. Our data strongly suggest that inhibition of the purine degradation pathway might represent a novel approach to control plant pathogenic fungi and oomycetes.

Deep modifications of the microbiome of rice roots infected by the parasitic nematode Meloidogyne graminicola in highly infested fields in Vietnam.

Meloidogyne graminicola, also known as the rice root-knot nematode, is one of the most damaging plant-parasitic nematode, especially on rice. This obligate soilborne parasite induces the formation of galls that disturb the root morphology and physiology. Its impact on the root microbiome is still not well described. Here, we conducted a survey in Northern Vietnam where we collected infected (with galls) and non-infected root tips from the same plants in three naturally infested fields. Using a metabarcoding approach, we discovered that M. graminicola infection caused modifications of the root bacterial community composition and network structure. Interestingly, we observed in infected roots a higher diversity and species richness (+24% observed ESVs) as well as a denser and more complex co-occurrence network (+44% nodes and +136% links). We identified enriched taxa that include several hubs, which could serve as potential indicators or biocontrol agents of the nematode infection. Moreover, the community of infected roots is more specific suggesting changes in the functional capabilities to survive in the gall environment. We thus describe the signature of the gall microbiome (the 'gallobiome') with shifting abundances and enrichments that lead to a strong restructuration of the root microbiome.

Comparison of the penetration, development and reproduction of Meloidogyne javanica and M. graminicola on partially resistant Oryza sativa cultivars from East Africa

Summary The host response to Meloidogyne javanica infection of selected Oryza sativa and NERICA (New Rice for Africa) genotypes that are commonly grown in Tanzania and East Africa was examined. The O. sativa genotypes ‘Komboka’ and ‘Supa’ appeared to be partially resistant. A further experiment showed that both genotypes are also partially resistant to M. graminicola infection. The host response of ‘Komboka’ and ‘Supa’ to M. javanica and M. graminicola was further examined and compared in indoor growth chamber conditions. The genotypes ‘TOG5674’, ‘TOG5675’, ‘CG11’ and ‘CG14’ (both O. glaberrima) were included as the resistant reference genotypes for M. graminicola and the genotype ‘UPLRi-5’ (O. sativa) was included as the susceptible reference genotype for both species of root-knot nematodes. Meloidogyne graminicola was more aggressive on ‘Komboka’ and ‘Supa’ than M. javanica. Significantly less root galling was observed on ‘Komboka’ and ‘Supa’ than on ‘UPLRi-5’. In ‘Komboka’ and ‘Supa’ significantly fewer second-stage juveniles (J2) were able to penetrate the roots, to develop into adult females and to reproduce compared with ‘UPLRi-5’. Differential emigration of J2 from the roots of ‘Komboka’ and ‘Supa’ compared with ‘UPLRi-5’ contributed to the observed partial resistance in these genotypes to M. graminicola and M. javanica. Nematodes that successfully penetrated and developed in ‘Komboka’ and ‘Supa’ showed aberrant phenotypes. ‘Supa’ and ‘Komboka’ may be recommended for use by farmers in M. javanica and M. graminicola-infested fields.

Transcriptome Profiling Analysis Reveals Co-regulation of Hormone Pathways in Foxtail Millet during Sclerospora graminicola Infection.

Sclerospora graminicola (Sacc.) Schroeter is a biotrophic pathogen of foxtail millet (Setaria italica) and increasingly impacts crop production. We explored the main factors for symptoms such as dwarfing of diseased plants and the “hedgehog panicle” by determining panicle characteristics of varieties infected with S. graminicola and analyzing the endogenous hormone-related genes in leaves of Jingu 21. Results indicated that different varieties infected by S. graminicola exhibited various symptoms. Transcriptome analysis revealed that the ent-copalyl diphosphate synthetase (CPS) encoded by Seita.2G144900 and ent-kaurene synthase (KS) encoded by Seita.2G144400 were up-regulated 4.7-fold and 2.8-fold, respectively. Results showed that the biosynthesis of gibberellin might be increased, but the gibberellin signal transduction pathway might be blocked. The abscisic acid (ABA) 8′-hydroxylase encoded by Seita.6G181300 was continuously up-regulated by 4.2-fold, 2.7-fold, 14.3-fold, and 12.9-fold from TG1 to TG4 stage, respectively. Seita.2G144900 and Seita.2G144400 increased 79-fold and 51-fold, respectively, at the panicle development stage, promoting the formation of a “hedgehog panicle”. Jasmonic acid-related synthesis enzymes LOX2s, AOS, and AOC were up-regulated at the early stage of infection, indicating that jasmonic acid played an essential role in early response to S. graminicola infection. The expression of YUC-related genes of the auxin synthesis was lower than that of the control at TG3 and TG4 stages, but the amidase encoded by Seita.2G313400 was up-regulated by more than 30-fold, indicating that the main biosynthesis pathway of auxin had changed. The results suggest that there was co-regulation of the hormone pathways during the infection of foxtail millet by S. graminicola.

Systemic defense activation by COS-OGA in rice against root-knot nematodes depends on stimulation of the phenylpropanoid pathway

Activation of induced plant resistance to control pests and diseases is regaining attention in the current climate where chemical pesticides are being progressively banned. Formulations of chitosan oligomers (COS) and pectin-derived oligogalacturonides (OGA), COS-OGA, have previously been described to induce resistance against fungal diseases in different crop plants. Here, we investigated their potential and mode-of-action as preventive measures to control root-knot nematode Meloidogyne graminicola infection in rice.The results show a significant reduction in root-galling and nematode development in rice plants that were treated through foliar application with the COS-OGA formulations FytoSol® and FytoSave® 24 h before nematode inoculation. Hormone measurements, gene expression analyses, corroborated by treatments on salicylic acid (SA) and jasmonic acid (JA)-mutants indicated that the systemic COS-OGA induced defense mechanism against nematodes is not based on SA or JA activation. However, phenylalanine ammonia lyase (PAL) gene expression in roots as well as enzymatic PAL activity in the shoots were significantly induced 24 h after foliar COS-OGA spraying in comparison with untreated plants. COS-OGA-induced systemic defense was abolished in the rice OsPAL4-mutant, demonstrating that COS-OGA-induced defense is dependent on OsPAL4 activation in rice plants.

Strigolactones enhance root-knot nematode (Meloidogyne graminicola) infection in rice by antagonizing the jasmonate pathway.

Summary Strigolactones (SLs) are carotenoid‐derived plant hormones that also act in the rhizosphere to stimulate germination of root‐parasitic plants and enhance plant symbiosis with beneficial microbes. Here, the role of SLs was investigated in the interaction of rice (Oryza sativa) roots with the root‐knot nematode Meloidogyne graminicola.Genetic approaches and chemical sprays were used to manipulate SL signaling in rice before infection with M. graminicola. Then, nematode performance was evaluated and plant defense hormones were quantified. Meloidogyne graminicola infection induced SL biosynthesis and signaling and suppressed jasmonic acid (JA)‐based defense in rice roots, suggesting a potential role of SLs during nematode infection. Whereas the application of a low dose of the SL analogue GR24 increased nematode infection and decreased jasmonate accumulation, the SL biosynthesis and signaling d mutants were less susceptible to M. graminicola, and constitutively accumulated JA and JA‐isoleucine compared with wild‐type plants. Spraying with 0.1 μM GR24 restored nematode susceptibility in SL‐biosynthesis mutants but not in the signaling mutant. Furthermore, foliar application of the SL biosynthesis inhibitor TIS108 impeded nematode infection and increased jasmonate levels in rice roots.In conclusion, SL signaling in rice suppresses jasmonate accumulation and promotes root‐knot nematode infection.

T-DNA activation tagging in rice results in a variable response to Meloidogyne graminicola infection

Plant-parasitic nematodes (PPNs) are known to be devastating pests of agricultural crops; the rice root knot nematode Meloidogyne graminicola being the most damaging in rice. Variability in response to any trait is important not only to understand plant-stress interactions, but also its utility in stress mitigation. In this direction, the focus of the study was to exploit activation tagging, a well-established functional genomics approach in rice as a plausible strategy to assess variability in the phenotypic and molecular response to M. graminicola infection. T-DNA insertional mutants were developed in rice (acc. JBT 36/14) using an apical meristem-targeted in planta transformation strategy. A panel of 30 mutants that demonstrated molecular evidences for T-DNA integration and portraying a robust phenotype were chosen for the study. Vigorous phenotyping of these mutants against M. graminicola second stage juveniles both under in vitro pluronic gel medium and soil conditions depicted variable response based on four disease scoring parameters and the derived nematode reproductive factor. Among 30 mutants that were evaluated, five showed a resistant phenotype while 25 depicted a susceptible reaction. The resistant plants clearly demonstrated a reduction in all the disease parameters both under in vitro as well as greenhouse conditions. Quantification of transcripts of 25 genes associated with host defence responses belonging to salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) pathways also indicated corroboration with the phenotype exhibited by the mutants. Distinct pattern of gene expression profiles was observed not only between the susceptible and resistant mutants, but also amongst the resistant ones, demonstrating the possibility of lesser known defense pathways being operated in these plants, apparently depending upon the T-DNA integration loci. The variability in the response to nematode challenge demonstrated in this study can be a step towards deciphering of compatible/incompatible relationships that can form a knowledge base towards not only understanding plant-nematode interactions but also extrapolation of their utility in rice improvement programmes.