Nitric Oxide as a Beneficial Signaling Molecule in Trichoderma atroviride TRS25-Induced Systemic Defense Responses of Cucumber Plants Against Rhizoctonia solani.

Justyna Nawrocka,Urszula Małolepsza,Aleksandra Gromek

doi:10.3389/fpls.2019.00421

Justyna Nawrocka, Urszula Małolepsza + Show 1 more

Open Access

https://doi.org/10.3389/fpls.2019.00421

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Journal: Frontiers in plant science	Publication Date: Apr 17, 2019
Citations: 29	License type: CC BY 4.0

Affiliation: University of Łódź

Abstract

In the present study, Trichoderma atroviride TRS25 is presented as a biological control agent, which significantly limits the development of infection and reduces the disease caused by the pathogenic fungus Rhizoctonia solani in cucumber plants (Cucumis sativus L.). The systemic disease suppression is related to oxidative, signaling, and biochemical changes, that are triggered in response to a pathogen. Induction of systemic defense in cucumber by TRS25 greatly depends on the accumulation of signaling molecules including hydrogen peroxide (H2O2) and nitric oxide (NO) as well as salicylic acid (SA) and its derivatives including methyl salicylate (MeSA) and octyl salicylate (OSA). The study established that NO was accumulated in leaves and shoots of the cucumber plants, especially those pretreated with Trichoderma and inoculated with R. solani, where the compound was accumulated mainly in the cells localized in the vascular bundles and in epidermal tissues. We suggest, for the first time, that in the plants pretreated with TRS25, the accumulation of H2O2 and NO may be related to catalase (CAT) and S-nitrosoglutathione reductase (GSNOR) activity decrease. On the other hand, excessive accumulation of NO and SA may be controlled by forming their inactive forms, S-nitrosothiols (SNO) and salicylic acid glucosylated conjugates (SAGC), respectively. The obtained results suggest that the mentioned molecules may be an important component of the complex signaling network activated by TRS25, which is positively involved in systemic defense responses of cucumber plants against R. solani.

Highlights

Trichoderma spp. are the most common saprophytic fungi in the rhizosphere and they are very effective biological control agents (BCAs) impairing pathogens with different antagonistic strategies
Disease symptoms were identified in all Rs plants based on the formation of extensive brown lesions and rot symptoms on the roots followed by shoot and leaf dark brown blight blotches and plant collapse (Figure 1A)
We present results which show that T. atroviride TRS25 is BCA, which significantly limits the development of infection and disease caused by the pathogenic fungus R. solani in cucumber plants (C. sativus L.)

Summary

Introduction

Trichoderma spp. are the most common saprophytic fungi in the rhizosphere and they are very effective biological control agents (BCAs) impairing pathogens with different antagonistic strategies. Induction of plant defense mechanisms or “sensitization” of plants by prior application of Trichoderma is thought to be a promising plant protection strategy. Their beneficial influence on plants depends on the Trichoderma strain, plant species, pathogen, and TRS25-Induced Defense Against R. solani soil-climate conditions (Harman et al, 2004; Singh et al, 2010; Hermosa et al, 2012; Yousef et al, 2013; Gomes et al, 2017). Trichoderma may induce accumulation of antimicrobial compounds such as phenolics as well as it may cause cell wall reinforcement by lignin and callose deposition (Bolton, 2009; Salas-Marina et al, 2011; Harman et al, 2012; Mayo et al, 2015)

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