Temporary heat stress suppresses PAMP‐triggered immunity and resistance to bacteria in Arabidopsis thaliana

Abstract

Summary Recognition of pathogen‐associated molecular patterns (PAMPs) is crucial for plant defence against pathogen attack. The best characterized PAMP is flg22, a 22 amino acid conserved peptide from flagellin protein. In Arabidopsis thaliana, flg22 is recognized by the flagellin sensing 2 (FLS2) receptor. In this study, we focused on biotic stress responses triggered by flg22 after exposure to temporary heat stress (HS). It is important to study the reactions of plants to multiple stress conditions because plants are often exposed simultaneously to a combination of both abiotic and biotic stresses. Transient early production of reactive oxygen species (ROS) is a well‐characterized response to PAMP recognition. We demonstrate the strong reduction of flg22‐induced ROS production in A. thaliana after HS treatment. In addition, a decrease in FLS2 transcription and a decrease of the FLS2 presence at the plasma membrane are shown after HS. In summary, our data show the strong inhibitory effect of HS on flg22‐triggered events in A. thaliana . Subsequently, temporary HS strongly decreases the resistance of A. thaliana to Pseudomonas syringae . We propose that short exposure to high temperature is a crucial abiotic stress factor that suppresses PAMP‐triggered immunity, which subsequently leads to the higher susceptibility of plants to pathogens.

Fight hard or die trying: when plants face pathogens under heat stress

“…Alternatively, TpE represses FLS2 expression, salicyclic acid (SA) biosynthesis and signalling and SAR‐related gene expression. Also, TpE impairs PTI‐related ROS production and decreases SA levels (Rasmussen et al ., 2013; Huot et al ., 2017; Janda et al ., 2019). At the chromatin level, TpE promotes the rapid replacement of H2A.Z, mediated by HSFA1, allowing the expression of heat‐responsive and defence‐related genes (Cheng et al ., 2013; Cortijo et al ., 2017).…”

“…Two studies that were performed in A. thaliana reported the repression of systemic acquired resistance (SAR)‐related gene expression of the ICS1‐mediated SA biosynthesis and signalling pathway, as well as a lower SA accumulation level upon TpE and flg22 treatment (Rasmussen et al ., 2013; Huot et al ., 2017). Conversely, a recent study showed that a short, but extremely high, TpE combined with flg22 treatment represses the expression of flagelin sensing 2 ( FLS2 ) receptor gene and transiently inhibits ROS production, whereas the expression of FRK1 and ICS1 , two PTI‐responsive genes, was not induced (Janda et al ., 2019). By contrast, TpE combined with flg22 treatment of A. thaliana protoplasts leads to the induction of WRK29 and FRK1 PTI‐responsive genes and to increased phosphorylation of the serine/threonine kinase BIK1 and of MAPKs (Cheng et al ., 2013).…”

Every cloud has a silver lining: how abiotic stresses affect gene expression in plant-pathogen interactions

“…In the present context of climate change, understanding how hormone-dependent gene expression is altered by ever-changing temperatures is of great interest. In the past few years, several reports have shown that the defensive responses mediated by SA during the interaction between Arabidopsis and Pseudomonas syringae are increased at low temperature (16 °C; Li et al , 2020 ), and compromised under high (28 °C; Wang et al , 2009 ) and extreme temperatures (37 °C and 42 °C; Janda et al , 2019 ). Interestingly, extreme temperatures compromise defense even when the exposure is short ( Janda et al , 2019 ).…”

“…In the past few years, several reports have shown that the defensive responses mediated by SA during the interaction between Arabidopsis and Pseudomonas syringae are increased at low temperature (16 °C; Li et al , 2020 ), and compromised under high (28 °C; Wang et al , 2009 ) and extreme temperatures (37 °C and 42 °C; Janda et al , 2019 ). Interestingly, extreme temperatures compromise defense even when the exposure is short ( Janda et al , 2019 ). An elegant study by Huot et al , (2017) reported that at an elevated temperature of 30 °C, Arabidopsis plants exposed to the synthetic SA analogue benzothiadiazole did not accumulate mRNA of the two SA-marker genes ICS1 and PR1 (see Supplementary Table S1 for a list of all Arabidopsis genes mentioned in this review).…”

Phospholipase Dα1 mediates the high-Mg2+ stress response partially through regulation of K+ homeostasis

“…Roots from 6 plants were used to prepare one sample. The soluble fraction was prepared according to Janda et al(2019). Briefly, roots were homogenized using homogenization buffer (50 mM HEPES-NaOH, pH 7.5, 0.4 M sucrose, 0.1 M KCl, 0.1 M MgCl 2 ) with a protease inhibitor cocktail (P 9599, Sigma) and Pierce Phosphatase Inhibitor Mini Tablets (A23957, Thermo Fisher Scientific).…”