Phytohormone Priming of Tomato Plants Evoke Differential Behavior in Rhizoctonia solani During Infection, With Salicylate Priming Imparting Greater Tolerance Than Jasmonate

Abstract

In the field of phytohormone defense, the general perception is that salicylate (SA)-mediated defense is induced against biotrophic pathogens while jasmonate (JA)-mediated defense functions against necrotrophic pathogens. Our goals were to observe the behavior of the necrotrophic pathogen Rhizoctonia solani in the vicinity, on the surface, and within the host tissue after priming the host with SA or JA, and to see if priming with these phytohormones would affect the host defense differently upon infection. It was observed for the first time, that R. solani could not only distinguish between JA versus SA-primed tomato plants from a distance, but surprisingly avoided SA-primed plants more than JA-primed plants. To corroborate these findings, early infection events were monitored and compared through microscopy, Scanning Electron Microscopy, and Confocal Laser Scanning Microscopy using transformed R. solani expressing green fluorescence protein gene (gfp). Different histochemical and physiological parameters were compared between the unprimed control, JA-primed, and SA-primed plants after infection. The expression of a total of fifteen genes, including the appressoria-related gene of the pathogen and twelve marker genes functioning in the SA and JA signaling pathways, were monitored over a time course during early infection stages. R. solani being traditionally designated as a necrotroph, the major unexpected observations were that Salicylate priming offered better tolerance than Jasmonate priming and that it was mediated through the activation of SA-mediated defense during the initial phase of infection, followed by JA-mediated defense in the later phase. Hence, the present scenario of biphasic SA-JA defense cascades during R. solani infection, with SA priming imparting maximum tolerance, indicate a possible hemibiotrophic pathosystem that needs to be investigated further.

Physio‐biochemical and histological alterations in response to sheath blight disease of rice (Oryza sativaL.)

“…These genes are induced by a fungal attack and are involved in the SA defence response pathway (Agati et al, 2012). Previously, the expression profiles of two flavonoid synthesizing genes (CHS1 & CHS2) were analysed during R. solani infection by Koley et al (2022), and their results indicate that these genes have been linked to the early induced defence response in hosts against the pathogen. The synthesis of an important rice flavonoid, i.e., sakuranetin, is also dependent on CHS activation (Koley et al, 2022).…”

“…Previously, the expression profiles of two flavonoid synthesizing genes (CHS1 & CHS2) were analysed during R. solani infection by Koley et al (2022), and their results indicate that these genes have been linked to the early induced defence response in hosts against the pathogen. The synthesis of an important rice flavonoid, i.e., sakuranetin, is also dependent on CHS activation (Koley et al, 2022). However, Samal et al (2022) recorded a significantly higher accumulation of CHS transcripts in CR 1014 (the international tolerant variety) than in the Swarna‐Sub1 (the susceptible variety).…”

“…These genes are induced by a fungal attack and are involved in the SA defence response pathway (Agati et al, 2012). Previously, the expression profiles of two flavonoid synthesizing genes (CHS1 & CHS2) were analysed during R. solani infection by Koley et al (2022),…”

Chemical priming of plant defense responses to pathogen attacks

“…Chemical priming (of SAR) can be achieved via direct application of SA and NHP ( Kauss et al., 1992b ; Yi et al., 2014 ; Yi et al., 2015 ; Hartmann and Zeier, 2019 ; Yildiz et al., 2021 ), application of their precursors ( Bernsdorff et al., 2016 ; Hartmann et al., 2018 ), or induction of their biosynthesis pathways ( Návarová et al., 2012 ; Hartmann et al., 2018 ; Koley et al., 2022 ). The mobilization of SA and NHP is important in the process of chemical priming.…”

Comparative Study of Three Biological Control Agents and Two Conventional Fungicides against Coriander Damping-off and Root Rot Caused by Rhizoctonia solani

“…On the other hand, R. solani-infected plants reduced SA production, causing an increment in disease severity. The protective action of Trichoderma may go back to its role in mediating the signal pathways of ethylene/jasmonate and salicylic acid [71]. Niu et al [72] stated that B. cereus-induced Arabidopsis systematically acquired resistance through the SA signaling pathway to enhance its disease resistance.…”