Effect of powdery mildew infection on some physiological and molecular markers of wild type and hormone mutant barley plants

BackgroundGrapevine (Vitis vinifera) productivity has been severely affected by various bacterial, viral and fungal diseases worldwide. When a plant is infected with the pathogen, various defense mechanisms are subsequently activated in plants at various molecular levels. Thus, for substantiating the disease control in an eco-friendly way, it is essential to understand the molecular mechanisms governing pathogen resistance in grapes.ResultsIn our study, we performed genome-wide identification of various defensive genes expressed during powdery mildew (PM) and downy mildew (DM) infections in grapevine. Consequently, we identified 6, 21, 2, 5, 3 and 48 genes of Enhanced Disease Susceptibility 1 (EDS1), Non-Race-specific Disease Resistance (NDR1), Phytoalexin deficient 4 (PAD4), Nonexpressor of PR Gene (NPR), Required for Mla-specified resistance (RAR) and Pathogenesis Related (PR), respectively, in the grapevine genome. The phylogenetic study revealed that V. vinifera defensive genes are evolutionarily related to Arabidopsis thaliana. Differential expression analysis resulted in identification of 2, 4, 7, 2, 4, 1 and 7 differentially expressed Nucleotide-binding leucine rich repeat receptor (NLR), EDS1, NDR1, PAD4, NPR, RAR1 and PR respectively against PM infections and 28, 2, 5, 4, 1 and 19 differentially expressed NLR, EDS1, NDR1, NPR, RAR1 and PR respectively against DM infections in V. vinifera. The co-expression study showed the occurrence of closely correlated defensive genes that were expressed during PM and DM stress conditions.ConclusionThe PM and DM responsive defensive genes found in this study can be characterized in future for impelling studies relaying fungal and oomycete resistance in plants, and the functionally validated genes would then be available for conducting in-planta transgenic gene expression studies for grapes.

Under field conditions, plants are often exposed to more than one stress factor at the same time, and therefore need to adapt to different combinations of stresses. Crosstalk between responses to abiotic and biotic stresses is known to occur, and the interaction between stress responses can be positive or negative. We studied the interaction of drought stress and powdery mildew (PM) infection in tomatoes using near-isogenic tomato lines (NILs) carrying the Ol-1, ol-2, or Ol-4 gene that confers resistance to tomato PM caused by Oidium neolycopersici. Our study demonstrated that drought-induced growth reduction was not further reduced by powdery mildew infection. Drought stress, however, decreased fungal infection in the susceptible genotype Moneymaker (MM) with fungal biomass tending to decrease further as the drought severity increased. Drought stress did not affect PM resistance levels of resistant NIL carrying ol-2 (a mutant of the tomato susceptibility Mlo gene) and Ol-4 an NLR (nucleotide-binding site-LRR) R gene associated with a fast hypersensitivity response (HR) but tended to slightly decrease disease levels of NIL-Ol-1 (no gene characterized yet, associated with a slow HR following PM infection). At the molecular level, genes involved in abscisic acid (ABA), salicylic acid (SA), and ethylene pathways were highly induced under combined stress indicating the involvement of ABA, SA, and ethylene in the crosstalk between abiotic and biotic stress. Messenger RNA expression of the ABA-responsive dehydrin SlTAS14 was induced under drought and combined stress with the highest induction under combined stress, and resistant NIL lines showed higher expression levels than MM. The expression of SlNCED (involved in ABA synthesis) was also upregulated under drought and highly induced under combined stress. Expression levels of pathogen responsive gene SlPR1 (an indicator of the SA pathway) and SlACS (involved in ethylene synthesis) were highly induced under powdery mildew infection in MM and the Ol-1 and were induced the most under combined stress in these lines. Taken together, these findings indicate that drought stress can interact with and influence PM infection in tomatoes in a resistance type-dependent manner. The role of hormonal signaling pathways in the crosstalk between drought stress and PM infection is further discussed.

Impact of Elevated Atmospheric CO2 Level on Powdery Mildew (Blumeria graminis f.sp. tritici) Severity in Wheat Depends on the Pathotype × Genotype Interaction

Multiple fungal diseases resistance induction in Cucumis melo through co-transformation of different pathogenesis related (PR) protein genes

Reactions of tobacco genotypes with different antioxidant capacities to powdery mildew and Tobacco mosaic virus infections

Cultivated wheat varieties have different degrees of resistance against powdery mildew. Cyclic hydroxamic acids are key defence chemicals of wheat. Examinations comprised the measurement of cyclic hydroxamic acid content and powdery mildew infection of three varieties (Lukullus, Lennox, Ispan) and a hybrid (Hystar) of field cultivated wheat, and the effectivity of two biological (Polyversum and Trifender) and one conventional fungicide (Solyom) on powdery mildew. Sample collection and measurement of fungus infection were carried out on three occasions: at BBCH 23-24, BBCH 32-33 and BBCH 77-83 phenological phases. Variety/hybrid and sampling time has significant effect on cyclic hydroxamic acid content, but there was no direct correlation between hydroxamic acid content and powdery mildew infection. Differences were found amongst varieties/hybrid in powdery mildew infection too. Only the hybrid, Hystar, showed considerable infection at every sampling time. The conventional chemical out of fungicides alone proved to be effective, and its effectivity lasted for five weeks.

The relationship between N nutrition, plant metabolism and powdery mildew infection, an important disease in glasshouse cucumber production, was studied on plants grown in nutrient solution. Strong N deficiency did not restrain infection but instead restrained growth of the fungus after successful infection. This was presumably due to a shortage of some amino acids. NO3 excess diminished hyphae development. This was not caused by factors which are generally discussed in relation to powdery mildew development like carbohydrate content and activity of enzymes of phenol metabolism. Powdery mildew infection could not be reduced by controlled N nutrition without yield reduction.

Silicon supply in soilless cultivations of zucchini alleviates stress induced by salinity and powdery mildew infections

Germin gene expression is induced in wheat (Triticum aestivum L.) leaves by powdery mildew (Erysiphe graminis f. sp. tritici) infection. Germin is a protein marker for early cereal development and is an oxalate oxidase, an enzyme that catalyzes the conversion of oxalate to CO2 and H2O2. The induction of germin gene expression by powdery mildew infection is consistent with the importance of H2O2 to plant defense and identifies a mechanism for the elevation of H2O2 levels in wheat leaves. Germin mRNA levels increased 2 d after inoculation of seedlings with powdery mildew and continued to increase throughout an 8-d time course. The increase in accumulation of germin mRNA was accompanied by an increase in the germin oligomer, which reached maximal levels by d 6. An increase in oxalate oxidase activity paralleled germin oligomer accumulation. Germin gene expression was induced in a relatively resistant cultivar (Bobwhite) as well as in a susceptible cultivar (Cheyenne), suggesting that the induction of germin gene expression is an indicator of powdery mildew infection rather than cultivar resistance.

Watermelon is an important vegetable crop and is widely cultivated in USA with an approximate global production of > 100 million tons. Powdery mildew (PM) caused by Podosphaera xanthii is a major production-limiting factor on watermelon and other cucurbits. Numerous PM and multiple disease resistant (MDR) watermelon germplasm lines have been developed by the USDA in Charleston, SC. To gain a better understanding of the innate and activated molecular defense mechanisms involved during compatible and incompatible PM-watermelon interactions, we inoculated PM susceptible (USVL677-PMS) and resistant (USVL531-MDR) watermelon plants with 105 conidia ml−1 of P. xanthii. RNA-seq profiling was done on leaf samples collected at 0, 1, 3, and 8 days post inoculation (DPI). A total of 2,566 unique differentially expressed genes (DEGs) were identified between compatible and incompatible interactions with P. xanthii. The compatible interactions resulted in distinct plant gene activation (> twofold unique transcripts, 335:191:1762 :: 1:3:8 DPI) as compared to incompatible interaction (> twofold unique transcripts, 314:681:487 :: 1:3:8 DPI). Further, comparative whole-genome resequencing analysis of USVL531-PMR, USVL677-PMS and four introgressed PM resistant recombinant inbred lines (RIL, USVL531-PMR × USVL677-PMS) were performed to identify the region of PM resistance introgressed break points along with other traits inherent by USVL531-PMR by comparing the SNPs and InDels. Based on SNPs identification and CAPS markers, the resistance gene was identified as ClaPMR2, Citrullus lanatus PM Resistance gene 2 {Chr2 : 26750001 .. 26753327 (−)}, a NBS-LRR resistance protein (R) with homology to the Arabidopsis thaliana PM resistance protein, RPW8. The transcriptome data also revealed a complex regulatory network associated with the introgressed junctions mediated by PM resistance R proteins (R genes) that may involve multiple signal regulators and transducers, carbohydrate metabolism, cell wall modifications and the hormone-signaling pathway.

Previous work has demonstrated that glycerol-3-phosphate (G3P) and oleic acid (18:1) are two important signal molecules associated with plant resistance to fungi. In this article, we provide evidence that a 3% glycerol spray application 1–2 days before powdery mildew infection and subsequent applications once every 4 days was sufficient to stimulate the plant defense responses without causing any significant damage to wheat leaves. We found that G3P and oleic acid levels were markedly induced by powdery mildew infection. In addition, TaGLI1 (encoding a glycerol kinase) and TaSSI2 (encoding a stearoylacyl carrier protein fatty acid desaturase), two genes associated with the glycerol and fatty acid (FA) pathways, respectively, were induced by powdery mildew infection, and their promoter regions contain some fungal response elements. Moreover, exogenous application of glycerol increased the G3P level and decreased the level of oleic acid (18:1). Glycerol application induced the expression of pathogenesis-related (PR) genes (TaPR-1, TaPR-2, TaPR-3, TaPR-4, and TaPR-5), induced the generation of reactive oxygen species (ROS) before powdery mildew infection, and induced salicylic acid (SA) accumulation in wheat leaves. Further, we sprayed glycerol in a wheat field and found that it significantly (p < 0.05) reduced the severity of powdery mildew disease and lessened disease-associated kernel weight loss, all without causing any noticeable degradation in wheat seed quality.

The enhanced disease resistance 1 (edr1) mutant of Arabidopsis confers enhanced resistance to bacterial and fungal pathogens. To better understand how edr1-mediated resistance occurs, we performed transcriptome analyses on wild-type and edr1 plants inoculated with the fungal pathogen Golovinomyces cichoracearum (powdery mildew). The expression of many known and putative defence-associated genes was more rapidly induced, and to higher levels, in edr1 plants relative to the wild-type. Many of the genes with elevated expression encoded WRKY transcription factors and there was enrichment for their binding sites in promoters of the genes upregulated in edr1. Confocal microscopy of transiently expressed EDR1 protein showed that a significant fraction of EDR1 was localized to the nucleus, suggesting that EDR1 could potentially interact with transcription factors in the nucleus. Analysis of gene ontology annotations revealed that genes associated with the endomembrane system, defence, reactive oxygen species (ROS) production and protein kinases were induced early in the edr1 mutant, and that elevated expression of the endomembrane system, defence and ROS-related genes was maintained for at least 4 days after infection.

In grape (Vitis), stilbene phytoalexins can either be in situ synthesized or transported to the site of response during powdery mildew infection, enhancing disease resistance. Resveratrol is a phytoprotective stilbenoid compound that is synthesized by stilbene synthase (STS) in response to biotic and abiotic stresses, and is also known to have health benefits in the human diet. We have previously shown that transgenic Vitis vinifera cv. Thompson Seedless plants overexpressing a stilbene synthase gene, VqSTS6, from wild Chinese Vitis quinquangularis had a higher stilbenoid content, leading to an enhanced resistance to powdery mildew (Uncinula necator (Schw.) Burr). However, the biosynthesis and transportation in the plant tissue under powdery mildew infection are still unclear. Here, inhibitor and micro-grafting technologies were used to study the accumulation of resveratrol following powdery mildew infection. We observed that the levels of STS expression and stilbenoids increased in response to powdery mildew infection. Powdery mildew and inhibitor treatment on detached grape branches showed that resveratrol was in situ synthesized. Experiments with grafted plantlets showed that the abundance of stilbenoid compounds increased in the shoot during VqSTS6 overexpression in the root, while VqSTS6-Flag fusion was not tranported to the scions and only expressedin thetransgenic rootstocks. Compared with wild-type Thompson Seedless plants, the non-transgenic/VqSTS6 transgenic (scion/rootstock) grafted Thompson Seedless plantlets exhibited increased resistance to powdery mildew. In addition, overexpression of VqSTS6 in roots led to increased levels of stilbenoid compounds in five other European grape varieties (V. vinifera cvs. Chardonnay, Perlette, Cabernet Sauvignon, Riesling and Muscat Hamburg). In conclusion, stilbenoid compounds can be either in situ synthesized or transported to the site of powdery mildew infection, and overexpression of VqSTS6 in the root promotes stilbenoids accumulation and disease resistance in European grapevine varieties.

Powdery mildew pathogen [Erysiphe necator (Schw.) Burrill.] induced physiological and biochemical alterations in leaf tissue of grapevines (Vitis spp.)

Histo-chemical and biochemical analysis reveals association of er1 mediated powdery mildew resistance and redox balance in pea