Reactive oxygen species and plant resistance to fungal pathogens

Reactive oxygen species (ROS) have been studied for their role in plant development as well as in plant immunity. ROS were consistently observed to accumulate in the plant after the perception of pathogens and microbes and over the years, ROS were postulated to be an integral part of the defence response of the plant. In this article we will focus on recent findings about ROS involved in the interaction of plants with pathogenic fungi. We will describe the ways to detect ROS, their modes of action and their importance in relation to resistance to fungal pathogens. In addition we include some results from works focussing on the fungal interactor and from studies investigating roots during pathogen attack

The innate immune signaling system as a regulator of disease resistance and induced systemic resistance activity against Verticillium dahliae

In the last decades, the plant innate immune responses against pathogens have been extensively studied, while biocontrol interactions between soilborne fungal pathogens and their hosts have received much less attention. Treatment of Arabidopsis thaliana with the nonpathogenic bacterium Paenibacillus alvei K165 was shown previously to protect against Verticillium dahliae by triggering induced systemic resistance (ISR). In the present study, we evaluated the involvement of the innate immune response in the K165-mediated protection of Arabidopsis against V. dahliae. Tests with Arabidopsis mutants impaired in several regulators of the early steps of the innate immune responses, including fls2, efr-1, bak1-4, mpk3, mpk6, wrky22, and wrky29 showed that FLS2 and WRKY22 have a central role in the K165-triggered ISR, while EFR1, MPK3, and MPK6 are possible susceptibility factors for V. dahliae and bak1 shows a tolerance phenomenon. The resistance induced by strain K165 is dependent on both salicylate and jasmonate-dependent defense pathways, as evidenced by an increased transient accumulation of PR1 and PDF1.2 transcripts in the aerial parts of infected plants treated with strain K165

The bacterial biocontrol agent Paenibacillus alvei K165 confers inherited resistance against Verticillium dahliae

The biocontrol agent Paenibacillus alvei K165 was previously shown to protect Arabidopsis thaliana plants against Verticillium dahliae. Here we show that K165 also confers inherited immune resistance against V. dahliae. By performing a histone acetyltransferases mutant screen, ChIP-assays and transcriptomic experiments we were able to show that histone acetylation significantly contributes to the K165 biocontrol activity and establishment of inheritable resistance against V. dahliae. K165 treatment primed the expression of immune-related marker genes and the cinnamyl alcohol dehydrogenases CAD3 through the function of histone acetyltransferases. Our results reveal that offspring of plants treated with K165 have primed immunity and enhanced lignification both contributing towards the K165-mediated inherited immune resistance. Thus, our study paves that way for the use of biocontrol agents for the establishment of inheritable resistance against agronomically important pathogens

Insights into the role of ethylene perception in tomato resistance to vascular infection by Verticillium dahliae

A Tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS) system was employed to investigate the role of the tomato ethylene receptor ETR4. By comparing wilting symptoms of verticillium wilt in wild-type, ethylene-insensitive Never ripe (Nr) mutant tomato plants and ETR4-silenced plants, it was demonstrated that disease severity in the Nr and ETR4-silenced plants was statistically reduced compared to wild-type plants. Disease incidence and severity were reduced by 11 and 20%, respectively, in the Nr plants compared to the wild-type plants, at 33 days post-inoculation (d.p.i.). In the ETR4-silenced plants, disease incidence and severity were reduced by 14 and 15%, respectively, compared to the TRV-only-inoculated plants, at 37 d.p.i. Quantification of Verticillium dahliae by qPCR revealed that the reduction in symptom severity in the Nr plants was associated with significant reduction of growth of the pathogen in the vascular tissues of the Nr plants compared to that in the wild-type plants, suggesting that impaired perception of ethylene via the Never-ripe receptor results in increased disease resistance. Fungal reduction was evident at each sampling day in the Nr plants, ranging from 1·5 to 1·75 times less than that in the wild-type plants. Fungal quantification in the ETR4-silenced and TRV-only-inoculated plants showed similar levels of fungal biomas

Mode of action of a non-pathogenic Fusarium oxysporum strain against Verticillium dahliae using Real Time QPCR analysis and biomarker transformation

Verticillium wilt is a devastating disease of a wide range of herbaceous and woody plant hosts. It is incited by the soilborne fungus Verticillium dahliae. Management strategies are mainly focused on preventive measures. In a previous study, the efficacy of a non-pathogenic Fusarium oxysporum strain, designated as F2, isolated from a suppressive compost amendment, has been reported to reduce Verticillium wilt symptom development in eggplants under greenhouse and field conditions; in addition, antibiosis or parasitism were ruled out by using a dual culture test. In the present study, we investigated the mode of action of F2 against V. dahliae. For this purpose, the F2 and V. dahliae strains were transformed with the EGFP and DsRed2 reporter genes respectively, so as to visualize their presence on the root surface of eggplants. In addition, the ramification of both fungi into the plant vascular system was monitored by Real Time QPCR analysis. It was shown that F2 colonizes the root surface along the intercellular junctions excluding V. dahliae from the same ecological niche. In parallel, QPCR analysis showed that application of F2 reduces the levels of V. dahliae vascular colonization along with the disease severity. In a split root experiment it was demonstrated that F2 does not trigger the defense mechanisms of eggplants against V. dahliae. Therefore, it seems that competition for space or nutrients on the root surface are the main mechanism of action of F2 against V. dahlia

Ethylene perception via ETR1 is required in Arabidopsis infection by Verticillium dahliae

Vascular wilts caused by Verticillium spp. are very difficult to control and, as a result, are the cause of severe yield losses in a wide range of economically important crops. The responses of Arabidopsis thaliana mutant plants impaired in known pathogen response pathways were used to explore the components in defence against Verticillium dahliae. Analysis of the mutant responses revealed enhanced resistance in etr1-1 [ethylene (ET) receptor mutant] plants, but not in salicylic acid-, jasmonic acid- or other ET-deficient mutants, indicating a crucial role of ETR1 in defence against this pathogen. Quantitative polymerase chain reaction analysis revealed that the decrease in symptom severity shown in etr1-1 plants was associated with significant reductions in the growth of the pathogen in the vascular tissues of the plants, suggesting that impaired perception of ET via ETR1 results in increased disease resistance. Furthermore, the activation and increased accumulation of the PR-1, PR-2, PR-5, GSTF12, GSTU16, CHI-1, CHI-2 and Myb75 genes, observed in etr1-1 plants after V. dahliae inoculation, indicate that the outcome of the induced defence response of etr1-1 plants seems to be dependent on a set of defence genes activated on pathogen attac

Thermal inactivation of compost suppressiveness implicates possible biological factors in disease management

Verticillium wilt is a devastating disease of a wide range of herbaceous and woody plant hosts, incited by the soilborne fungus Verticillium dahliae. Since there are no chemical treatments to control the pathogen, management strategies are focused on preventive measures. In the present study, the microbial nature involved in the suppressiveness of a compost amendment (GR6, fabricated of horse manure, unbroken bedding hay + wood shavings and municipal green waste) against V. dahliae was investigated. For this purpose, eggplants grown in sterilised or non-sterilised compost were transplanted in soil infested with V. dahliae microsclerotia, amended or not with sterilised or non-sterilised compost. The most efficient treatments were those that included non-sterilised compost; therefore, the observed suppressiveness could be attributed to microbial agents. Several microbes were isolated from the root system of eggplants grown in the compost and tested in vitro against V. dahliae. Two bacterial strains identified as members of the Pseudomonas fluorescens complex and two fungal isolates belonging to Fusarium oxysporum were selected for further evaluation under glasshouse conditions. The ability of the microbial agents to reduce the percentage of diseased leaves compared to the control treatment was demonstrated. Moreover, it was shown that the most efficient bacterial strain was a rhizosphere and endophyte inhabitant. In a field experiment, the treatment where compost was applied both in the nursery and the field and treatments with F. oxysporum and P. fluorescens strains exhibited reduced disease severity; however, an increase in yield compared to the untreated control was not observe

The ethylene receptor ETR1 is required for Fusarium oxysporum pathogenicity

Fusarium oxysporum is a ubiquitous vascular wilt plant pathogen causing severe yield losses in a wide range of economically important crops. In this study, the interaction between Fusarium oxysporum f. sp. raphani and Arabidopsis thaliana plants impaired in the salicylate (SA), jasmonate (JA) and ethylene (ET) defence signalling pathways was investigated to better understand the nature of this plant-microbe interaction. The in planta bioassays revealed a key role for the ETR1 receptor as the etr1-1 mutant plants exhibited statistically less Fusarium wilt symptoms compared to the other mutant and Col-0 plants. Quantitative polymerase chain reaction (qPCR) analysis associated the decrease in symptom severity shown in etr1-1 plants with reduced vascular growth of the pathogen, suggesting the activation of defence mechanisms in etr1-1 plants against F. oxysporum. Furthermore, the early activation and increased accumulation of the SA-responsive PR1, PR2 and PR5 genes in the etr1-1 plants, in contrast to the Col-0 plants that showed higher transcript levels of the JA/ET-responsive PR3, PR4 and PDF1.2 genes after F. oxysporum inoculation, can lead to speculation that F. oxysporum hijacks ETR1-mediated ethylene signalling to promote disease development in plants

The ethylene receptor ETR1 is required for Fusarium oxysporum pathogenicity

Fusarium oxysporum is a ubiquitous vascular wilt plant pathogen causing severe yield losses in a wide range of economically important crops. In this study, the interaction between Fusarium oxysporum f. sp. raphani and Arabidopsis thaliana plants impaired in the salicylate (SA), jasmonate (JA) and ethylene (ET) defence signalling pathways was investigated to better understand the nature of this plant-microbe interaction. The in planta bioassays revealed a key role for the ETR1 receptor as the etr1-1 mutant plants exhibited statistically less Fusarium wilt symptoms compared to the other mutant and Col-0 plants. Quantitative polymerase chain reaction (qPCR) analysis associated the decrease in symptom severity shown in etr1-1 plants with reduced vascular growth of the pathogen, suggesting the activation of defence mechanisms in etr1-1 plants against F. oxysporum. Furthermore, the early activation and increased accumulation of the SA-responsive PR1, PR2 and PR5 genes in the etr1-1 plants, in contrast to the Col-0 plants that showed higher transcript levels of the JA/ET-responsive PR3, PR4 and PDF1.2 genes after F. oxysporum inoculation, can lead to speculation that F. oxysporum hijacks ETR1-mediated ethylene signalling to promote disease development in plants