Airborne signals from Trichoderma fungi stimulate iron uptake responses in roots resulting in priming of jasmonic acid‐dependent defences in shoots of Arabidopsis thaliana and Solanum lycopersicum

Abstract

Root colonization by Trichoderma fungi can trigger induced systemic resistance (ISR). In Arabidopsis, Trichoderma-ISR relies on the transcription factor MYB72, which plays a dual role in the onset of ISR and the activation of Fe uptake responses. Volatile compounds (VCs) from rhizobacteria are important elicitors of MYB72 in Arabidopsis roots. Here, we investigated the mode of action of VCs from Trichoderma fungi in the onset of ISR and Fe uptake responses. VCs from Trichoderma asperellum and Trichoderma harzianum were applied in an in vitro split-plate system with Arabidopsis or tomato seedlings. Locally, Trichoderma-VCs triggered MYB72 expression and molecular, physiological and morphological Fe uptake mechanisms in Arabidopsis roots. In leaves, Trichoderma-VCs primed jasmonic acid-dependent defences, leading to an enhanced resistance against Botrytis cinerea. By using Arabidopsis micrografts of VCs-exposed rootstocks and non-exposed scions, we demonstrated that perception of Trichoderma-VCs by the roots leads to a systemic signal that primes shoots for enhanced defences. Trichoderma-VCs also elicited Fe deficiency responses and shoot immunity in tomato, suggesting that this phenomenon is expressed in different plant species. Our results indicate that Trichoderma-VCs trigger locally a readjustment of Fe homeostasis in roots, which links to systemic elicitation of ISR by priming of jasmonic acid-dependent defences.

The role of volatiles in plant communication

“…However, when multiple volatile signals have to be integrated, the immune (or defence) response can also be reduced. Hormonal cross‐talk has a role in balancing trade‐offs, which can also result in the suppression of volatile emission (Martínez‐Medina et al ., ; Erb, ). Therefore, plants can produce specific volatiles upon microbial interactions but, in turn, microbes have been shown to be able to suppress VOC biosynthesis through the use of effectors (Sharifi et al ., ).…”

Root transcriptional dynamics induced by beneficial rhizobacteria and microbial immune elicitors reveal signatures of adaptation to mutualists

“…Besides promoting plant growth, WCS417 is also a potent elicitor of ISR. Recently, it was demonstrated that the onset of ISR in Arabidopsis and tomato coincides with the activation of the iron deficiency response in colonized roots Martinez-Medina et al, 2017). The onset of both ISR and the iron deficiency response by ISR-inducing rhizobacteria is marked by the activation of the root-specific transcription factor gene MYB72 and the high-affinity iron transporter gene IRON-REGULATED TRANSPORTER1 (IRT1; Van der Ent et al, 2008;Zamioudis et al, 2015).…”

Microbes Attaching to Endoparasitic Phytonematodes in Soil Trigger Plant Defense Upon Root Penetration by the Nematode

“…Root border cells and root exudates play a crucial role in shaping the microbial communities in the rhizosphere, eventually resulting in a positive plant-soil feedback (Bertin et al, 2003;Bais et al, 2006;Doornbos et al, 2012;De-la-Peña and Loyola-Vargas, 2014;Ma et al, 2017). Evidence is accumulating that certain beneficial microorganisms suppress plant-parasitic nematodes by inducing systemic resistance (ISR) in plants (Reitz et al, 2000;Munif et al, 2001;Siddiqui and Shaukat, 2004;Dababat and Sikora, 2007;Adam et al, 2014b;Selim et al, 2014;Martínez-Medina et al, 2017b;Elhady et al, 2018;Kang et al, 2018;Silva et al, 2018;. In the initial phase of microbially induced plant defense the pattern recognition receptors localized on the plant cell membranes recognize molecular structures on the microbe/ pathogen surface that are referred to as microbe/pathogenassociated molecular patterns (MAMP/PAMP) (Jones and Dangl, 2006).…”