Activation of Local and Systemic Defence Responses by Flg22 Is Dependent on Daytime and Ethylene in Intact Tomato Plants.

Attila Ördög,Kamirán Áron Hamow,Zalán Czékus,András Kukri,Péter Poór,Gabriella Szalai,Irma Tari

doi:10.3390/ijms22158354

Abstract

The first line of plant defence responses against pathogens can be induced by the bacterial flg22 and can be dependent on various external and internal factors. Here, we firstly studied the effects of daytime and ethylene (ET) using Never ripe (Nr) mutants in the local and systemic defence responses of intact tomato plants after flg22 treatments. Flg22 was applied in the afternoon and at night and rapid reactions were detected. The production of hydrogen peroxide and nitric oxide was induced by flg22 locally, while superoxide was induced systemically, in wild type plants in the light period, but all remained lower at night and in Nr leaves. Flg22 elevated, locally, the ET, jasmonic acid (JA) and salicylic acid (SA) levels in the light period; these levels did not change significantly at night. Expression of Pathogenesis-related 1 (PR1), Ethylene response factor 1 (ERF1) and Defensin (DEF) showed also daytime- and ET-dependent changes. Enhanced ERF1 and DEF expression and stomatal closure were also observable in systemic leaves of wild type plants in the light. These data demonstrate that early biotic signalling in flg22-treated leaves and distal ones is an ET-dependent process and it is also determined by the time of day and inhibited in the early night phase.

Highlights

Accepted: 31 July 2021Plants have co-evolved with microbes, including bacterial and fungal pathogens, under diverse environmental stimuli, which have resulted in the formation of a number of signalling pathways regulating local and systemic defence responses in higher plants
This increment in superoxide production was neither detected in the evening (Figure 1B) nor in Never ripe (Nr) leaves at all (Figure 1A,B), suggesting a daytime- and ethylenedependent regulation of superoxide production
Treatment with flg22 significantly increased this after 30 min in wild type (WT) leaves, but it did not change upon flg22 one hour later in WT plants (Figure 1C)

Summary

Introduction

Plants have co-evolved with microbes, including bacterial and fungal pathogens, under diverse environmental stimuli, which have resulted in the formation of a number of signalling pathways regulating local and systemic defence responses in higher plants. Defence responses of plants are regulated by several phytohormones which orchestrate the production of defensive proteins (e.g., pathogenesis-related (PR) proteins, defensins) or secondary metabolites (e.g., phytoalexins). SA plays a pivotal role in many plant–pathogen interactions, typically in defence against biotrophs and in the biotrophic stage of hemibiotrophs, by inducing localized death of infected cells, the hypersensitive response (HR) and the systemic acquired resistance (SAR) in long-distance tissues [5,6,7,8,9,10,11]

Objectives

Methods

Results

Discussion

Conclusion