Wheat Defense Response Research Articles

TaNAC8, a novel NAC transcription factor gene in wheat, responds to stripe rust pathogen infection and abiotic stresses

The plant-specific NAC domain proteins have been shown previously to play important roles in both abiotic and biotic stresses or in diverse developmental processes. In this research, the full-length cDNA sequence of a novel NAC (for NAM, ATAF1/2, CUC2) transcription factor gene, designated as TaNAC8, was isolated from wheat ( Triticum aestivum) using in silico cloning, reverse transcription polymerase chain reaction and 3’ rapid amplification of cDNA ends PCR methods. TaNAC8 was highly homologous to the rice OsNAC8 gene and predicted to encode a protein of 481 amino acids. The encoded TaNAC8 protein contained a NAC domain in the N-terminus and a transmembrane helices motif in the C-terminus. Using the yeast one-hybrid assay, we detected that the C-terminal region of the TaNAC8 protein had transcriptional activity. TaNAC8 was expressed strongly in the developing wheat seeds, but weakly in stems and flowers. The expression of TaNAC8 in leaves was induced by the infection of the stripe rust pathogen ( Puccinia striiformis f. sp. tritici) in the incompatible interaction at 24 h post inoculation, and also by treatments with methyl jasmonate and ethylene. However, salicylic acid and abscisic acid had no any significant effect on the gene expression. Several environmental stimuli, including high salinity, PEG (polyethylene glycol) treatment, and low-temperature, also enhanced the TaNAC8 expression. These results suggest that the novel TaNAC8 protein functions as a transcriptional activator involved in wheat defense responses to abiotic and biotic stresses.

Cloning and Characterization of a Pathogenesis-Related Protein Gene TaPR10 from Wheat Induced by Stripe Rust Pathogen

Pathogenesis-related proteins (PRs) play many important roles in plant defense response against pathogen attack. To better understand the molecular mechanism of PR genes involved in wheat adult plant resistance (APR) to stripe rust, based on a differentially expressed transcribed derived fragment (TDF), a novel PR gene from wheat cv. Xingzi 9104 infected by the Puccinia striiformis Westend f. sp. tritici Erikss. pathotype CY32, which was highly similar to the maize ZmPR10 gene and designated as TaPR10, was identified using in silico cloning and RT-PCR method. This novel TaPR10 gene was predicted to encode a 160-amino acid protein with a deduced molecular weight of 17.06 kDa and an isoelectronic point ( pI) of 5.19. An amino acid sequence analysis of TaPR10 demonstrated the presence of a typical conserved domain of pathogenesis related protein Bet_v_I family. Multiple alignment analysis based on the amino acids encoded by 10 different PR10 genes from maize ( Zea mays), rice ( Oryza sativa), broomcorn ( Sorghum bicolor), and wheat ( Triticum aestivum) indicated that PR proteins of class 10 was conserved among the 4 plant species with about 80% similarity. DNA sequence of TaPR10 suggested the presence of one 84-bp intron with the splicing sites of GT-AT bi-nucleotide sequence between 188 and 271 bp. Using a real-time quantitative RT-PCR (qRT-PCR), expression profiles of TaPR10 revealed that at the adult-plant stage, TaPR10 transcript was up-regulated as early as 12 h post-inoculation (hpi), with the occurrence of maximum induction at 24 hpi. At the seedling stage, TaPR10 was also slightly induced 18 hpi. However, the transcript amount was relatively lower than that of the adult-plant stage. Taken together, these results suggest that TaPR10 may participate in wheat defense response of APR to stripe rust.

Activation of Defense Mechanism in Wheat by Polyphenol Oxidase from Aphid Saliva

The saliva of two cereal aphids, Sitobion avenae and Schizaphis graminum in third-instar nymphs, was collected after 24 h of feeding by 30 aphids, separately, on artificial diet sachets, and the salivary enzymes were determined. The result showed that polyphenol oxidase (PPO) existed in the saliva of both aphid species, and the enzymatic activities were 6.2 x 10(-3) U/g for S. avenae and 2.37 x 10(-1) U/g for S. graminum, revealing a 38-fold higher activity in the saliva of S. graminum than in the saliva of S. avenae. It was speculated that the higher PPO activity in S. graminum saliva was a contributing factor to the light yellow spot left on the feeding site of the wheat leaf by S. graminum; no such spot was left by S. avenae. After treatment of a wheat seedling with the saliva of S. avenae and S. graminum and PPO at the concentration of aphid saliva, transcript profiling data showed that aphid saliva and PPO significantly induced expression of the genes aos and fps. Because genes aos and fps encode the key enzymes in the defense signal pathways jasmonic acid and terpene signal pathways, respectively, it was deduced that PPO from aphid saliva, as the main elicitor, triggers an appropriate defense response in wheat through jasmonic acid and terpene signal pathways.

Effects of -1,3-glucan from Septoria tritici on structural defence responses in wheat

The accumulation of the pathogenesis-related (PR) proteins beta-1,3-glucanase and chitinase and structural defence responses were studied in leaves of wheat either resistant or susceptible to the hemibiotrophic pathogen Septoria tritici. Resistance was associated with an early accumulation of beta-1,3-glucanase and chitinase transcripts followed by a subsequent reduction in level. Resistance was also associated with high activity of beta-1,3-glucanase, especially in the apoplastic fluid, in accordance with the biotrophic/endophytic lifestyle of the pathogen in the apoplastic spaces, thus showing the highly localized accumulation of defence proteins in the vicinity of the pathogen. Isoform analysis of beta-1,3-glucanase from the apoplastic fluid revealed that resistance was associated with the accumulation of an endo-beta-1,3-glucanase, previously implicated in defence against pathogens, and a protein with identity to ADPG pyrophosphatase (92%) and germin-like proteins (93%), which may be involved in cell wall reinforcement. In accordance with this, glycoproteins like extensin were released into the apoplast and callose accumulated to a greater extent in cell walls, whereas lignin and polyphenolics were not found to correlate with defence. Treatment of a susceptible wheat cultivar with purified beta-1,3-glucan fragments from cell walls of S. tritici gave complete protection against disease and this was accompanied by increased gene expression of beta-1,3-glucanase and the deposition of callose. Collectively, these data indicate that resistance is dependent on a fast, initial recognition of the pathogen, probably due to beta-1,3-glucan in the fungal cell walls, and this results in the accumulation of beta-1,3-glucanase and structural defence responses, which may directly inhibit the pathogen and protect the host against fungal enzymes and toxins.

Biochemical and molecular characterizations of Sitobion avenae-induced wheat defense responses

In this experiment, the aphid–wheat interaction system was chosen to study the changes in activity levels of key enzymes [lipoxygenase (LOX), polyphenoloxidase (PPO), phenylalanine ammonialyse (PAL) and β-1,3-glucanase] and in transcript level of key defense genes [encoding farnesyl pyrophosphate synthetase ( fps), encoding allene oxide synthase ( aos), and encoding phenylalanine ammonialyse ( pal)] under pressure of aphid-feeding, aphid-induced volatiles, as well as specific volatiles using enzymes assay, RT-PCR and real-time quantitative PCR techniques. At the same time, the induction of enzymatic and transcript levels of defense genes with artificial wounding, wounding-induced volatiles and inductive chemical agents (jasmonic acid and methyl salicylate) were also studied. Our results showed that the activities of key enzymes which belong to both jasmonic acid (JA) and salicylic acid (SA)-signaling pathways increased significantly with aphid-feeding. The relative transcript levels of key defense genes in the signaling pathways were also enhanced. So we propose that aphid-feeding could activate both jasmonic acid (JA) and salicylic acid (SA)-signaling transduction pathways. Mechanical wounding and aphid-feeding are not equivalent. Sitobion avenae-induced volatiles elicit the transcript of all three defense genes in neighboring plants, suggesting that the volatiles emitted from aphid-infested plants might induce the activity of LOX followed by activating the JA-signaling pathway and the transcript level of multiple defense genes that JA mediates. 6-Methyl-5-hepten-2-one, 2-tridecanone and ( E)-2-hexen-1-ol in S. avenae-induced volatiles not only activated the transcript level of defense genes, but also inhibited aphid-feeding behavior and population growth.

The Fusarium mycotoxin deoxynivalenol elicits hydrogen peroxide production, programmed cell death and defence responses in wheat

Fusarium species infect cereal crops worldwide and cause the important diseases Fusarium head blight and crown rot in wheat. Fusarium pathogens reduce yield and some species also produce trichothecene mycotoxins, such as deoxynivalenol (DON), during infection. These toxins play roles in pathogenesis on wheat and have serious health effects if present in grain consumed by humans or animals. In the present study, the response of wheat tissue to DON has been investigated. Infusion of wheat leaves with DON induced hydrogen peroxide production within 6 h followed by cell death within 24 h that was accompanied by DNA laddering, a hallmark of programmed cell death. In addition, real-time PCR analysis revealed that DON treatment rapidly induced transcription of a number of defence genes in a concentration-dependent manner. Co-treatment with DON and the antioxidant ascorbic acid reduced these responses, suggesting their induction may be at least partially mediated by reactive oxygen species (ROS), commonly known to be signalling molecules in plants. Wheat defence genes were more highly expressed in wheat stems inoculated with a DON-producing fungal strain than those inoculated with a DON-non-producing mutant, but only at a late stage of infection. Taken together, the results are consistent with a model in which DON production during infection of wheat induces ROS, which on the one hand may stimulate programmed host cell death assisting necrotrophic fungal growth, whereas, on the other hand, the ROS may contribute to the induction of antimicrobial host defences.

Fractionated Extracts of Russian Wheat Aphid Eliciting Defense Responses in Wheat

It is hypothesized that the interaction between aphids and plants follows a gene-for-gene model. The recent appearance of several new Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae), biotypes in the United States and the differential response of wheat, Triticum aestivum L., genotypes containing different resistance genes also suggest a gene-for-gene interaction. However, aphid elicitors remain unknown. This study was conducted to identify fractionated Russian wheat aphid extracts capable of eliciting differential responses between resistant and susceptible wheat genotypes. We extracted whole soluble compounds and separated proteins and metabolites from two Russian wheat aphid biotypes (1 and 2), injected these extracts into seedlings of susceptible wheat Gamtoos (dn7) and resistant 94M370 (Dn7), and determined phenotypic and biochemical plant responses. Injections of whole extract or protein extract from both biotypes induced the typical susceptible symptom, leaf rolling, in the susceptible cultivar, but not in the resistant cultivar. Furthermore, multiple injections with protein extract from biotype 2 induced the development of chlorosis, head trapping, and stunting in susceptible wheat. Injection with metabolite, buffer, or chitin, did not produce any susceptible symptoms in either genotype. The protein extract from the two biotypes also induced significantly higher activities of three defense-response enzymes (catalase, peroxidase, and β-glucanase) in 94M370 than in Gamtoos. These results indicate that a protein elicitor from the Russian wheat aphid is recognized by a plant receptor, and the recognition is mediated by the Dn7-gene product. The increased activities of defense-response enzymes in resistant plants after injection with the protein fraction suggest that defense response genes are induced after recognition of aphid elicitors by the plant.

Fractionated Extracts of Russian Wheat Aphid Eliciting Defense Responses in Wheat

It is hypothesized that the interaction between aphids and plants follows a gene-for-gene model. The recent appearance of several new Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae), biotypes in the United States and the differential response of wheat, Triticum aestivum L., genotypes containing different resistance genes also suggest a gene-for-gene interaction. However, aphid elicitors remain unknown. This study was conducted to identify fractionated Russian wheat aphid extracts capable of eliciting differential responses between resistant and susceptible wheat genotypes. We extracted whole soluble compounds and separated proteins and metabolites from two Russian wheat aphid biotypes (1 and 2), injected these extracts into seedlings of susceptible wheat Gamtoos (dn7) and resistant 94M370 (Dn7), and determined phenotypic and biochemical plant responses. Injections of whole extract or protein extract from both biotypes induced the typical susceptible symptom, leaf rolling, in the susceptible cultivar, but not in the resistant cultivar. Furthermore, multiple injections with protein extract from biotype 2 induced the development of chlorosis, head trapping, and stunting in susceptible wheat. Injection with metabolite, buffer, or chitin, did not produce any susceptible symptoms in either genotype. The protein extract from the two biotypes also induced significantly higher activities of three defense-response enzymes (catalase, peroxidase, and beta-glucanase) in 94M370 than in Gamtoos. These results indicate that a protein elicitor from the Russian wheat aphid is recognized by a plant receptor, and the recognition is mediated by the Dn7-gene product. The increased activities of defense-response enzymes in resistant plants after injection with the protein fraction suggest that defense response genes are induced after recognition of aphid elicitors by the plant.

The control of wheat defense responses during infection with Bipolaris sorokiniana by chitooligosaccharides

We studied the effects of low-molecular-weight water-soluble derivatives of chitin, chitooligsaccharides (ChOS) with a mol wt of 5–10 kD and the degree of acetylation of 65% on expression and molecular heterogeneity of peroxidase and the content of phytohormones in wheat plants differing in their resistance to the causal agents of root rots. Plant infection or their treatment with ChOS induced expression of the gene for anionic peroxidase and enhanced enzyme activity, and these processes depended on the degree of wheat resistance. They were more intense in the resistant cultivar. Treatment of susceptible plants with ChOS prevented a pathogen-induced drop in the cytokinin level, thus simulating defensive responses, which are characteristic of the resistant plants.

Cereal host interactions with Russian wheat aphid: A review

A lack of understanding the interaction between the Russian wheat aphid (RWA) and its host plant is a limitation in developing effective strategies for controlling the aphid. It is generally assumed that the interaction between aphid and plant is similar to that between plant and pathogen; that is, an elicitor from the insect is recognized by a protein from the host plant and a cascade of signal transduction events follows. However, evidence suggests that RWA feeding is eliciting both the SA- and JA/ethylene-dependent signaling pathways by mimicking aspects of both pathogen and herbivorous insect attacks. Results further suggest that phenotypic symptoms after RWA feeding are under regulation via two independent reactions, namely an immediate response (i.e., leaf rolling) and a downstream event (i.e., chlorosis). These defense responses enable a resistant host plant to defend itself and overcome the stress response, while their susceptible counterparts die. The processes involved in the onset of the defense response are discussed, and mechanisms enabling resistant plants to overcome the stress associated with the feeding process are presented as a working model for RWA-cereal host interaction. Knowledge of genes involved in wheat's defense responses against the RWA and an understanding of their functions may provide additional strategies for developing broad-spectrum resistance in plants.

The Canadian Phytopathological Society Annual Meeting, Montréal, Quebec, 2003

The Canadian Phytopathological Society Annual Meeting, Montréal, Quebec, 2003

Participation of ferulic acid in elicitation of winter wheat plants resistance against Septoria tritici infection

Aim. The usage of biotic elicitors for elicitation of defense responses may induce plant disease resistance and prevent increased environmental pollution by pesticides. The aim of research was to analyze in field trials participation of ferulic acid in elicitation of winter wheat resistance against Septoria tritici blotch agent. Methods. Content of endogenous H2O2, peroxidase, catalase and ascorbatperoxidase activities were measured in elicitor-treated and inoculated by S. tritici blotch winter wheat plants (cv. Poliska 90) during different ontogenesis phases. The extent of disease development, morphometric parameters and yield structure were analyzed. Results. The data obtained suggest that ferulic acid induced defense responses in winter wheat against S. tritici blotch agent. Initiation of defense responses in elicitor-treated plants occurred shortly. Hydrogen peroxide content was enhanced in elicitor-treated plants. Conclusions. Ferulic acid could be used as biotic elicitor. It increased the wheat grain quantity. Elicitation of biochemical nature of induced defense responses revealed increased peroxidase activities for lignin biosynthesis and mechanical strengthening of the plant cell walls.
 Keywords: winter wheat, biotic elicitors, induced resistance, ferulic acid, Triticum aestivum L., Septoria tritici.