IRE1-bZIP60 Pathway Is Required for Nicotiana attenuata Resistance to Fungal Pathogen Alternaria alternata

Abstract

As an endoplasmic reticulum (ER) stress sensor, inositol-requiring enzyme 1 (IRE1) splices the bZIP60 mRNA, and produces an active bZIP60 transcription factor that regulates genes involved in the unfolded protein response (UPR) during ER stresses. This IRE1-bZIP60 pathway is conserved in plant species and recently implicated in plant-pathogen interaction. However, it is unclear whether this IRE1-bZIP60 pathway is involved in Nicotiana attenuata resistance to necrotic fungal pathogen, Alternaria alternata. In this study, transcriptional levels of chaperone protein genes, including luminal binding protein (BiP), protein disulfide isomerase (PDI), calnexin 1-like (CNX 1-like), and calreticulin (CRT), and genes involved in IRE1-bZIP60 pathway, were all significantly induced in N. attenuata leaves after A. alternata inoculation. Silencing IRE1 or bZIP60 led to N. attenuata plants more susceptible to A. alternata, which were associated with reduced gene expressions of Feruloyl-CoA 6′-hydroxylase 1 (F6′H1), a gene encoding a key enzyme for phytoalexin scopoletin and scopolin biosynthesis. Further, electromobility shift assays (EMSA) indicated that bZIP60 protein of spliced form could directly bind to the promoter region of F6′H1 in vitro. JA signaling pathway is required for N. attenuata resistance to A. alternata. Interestingly, the fungus-elicited transcriptional levels of BiP, PDI, CNX 1-like, CRT, IRE1, and bZIP60(s) were all significantly decreased in JA-deficient or JA-insensitive plants. Meanwhile, those genes were significantly induced by methyl jasmonate (MeJA) when applied exogenously. However, the transcriptional levels of JA-regulated genes allene oxide synthase (AOS) and lipoxygenease 3 (LOX3) were not affected in plants impaired with IRE1-bZIP60 pathway. Thus, it is concluded that IRE1-bZIP60 pathway is required for N. attenuata resistance to A. alternata, and JA signaling pathway plays an important role in the elicitation of chaperone protein genes and IRE1-bZIP60 pathway.

Effects of Jasmonic Acid in ER Stress and Unfolded Protein Response in Tomato Plants

“…Our results showed that the micromolar concentration of exogenous JA significantly induced the transcript accumulation of BiP within 6 h in the leaves of tomato plants. This could have great importance because earlier, it has been found only that the exogenous application of JA or SA in millimolar concentration increased the expression of BiP genes in Arabidopsis [33] or in soybean [30]. In this work, JA was applied in two different micromolar concentrations, which could be closer to the natural endogenous changes in plants upon pathogen infection [74,75].…”

“…Firstly, Moreno et al [42] tested the effects of methyl jasmonate (MeJA) in Arabidopsis. Their results showed that 0.03 mM MeJA failed to activate bZIP60 mRNA processing within 5 h. More recently, Xu et al [33] demonstrated that MeJA in the concentration of 1 mM can transiently induce UPR marker genes within 3 h. The expression of BiP, protein disulfide isomerase (PDI), calnexin (CNX), and calreticulin (CRT) was at its maximum after 3 h but the transcript levels of bZIP60 were significantly higher after 12 h in Arabidopsis exposed to 1 mM MeJA [33]. These gene expression data suggest a rapid and concentration-dependent effect of MeJA, but the biochemical and physiological changes have neither been investigated in Arabidopsis nor in crops.…”

“…In conjugation with these, it has been demonstrated that several phytohormones are involved in the induction of ER stress and regulation of UPR, such as auxin or salicylic acid (SA) [29][30][31]. Although the role of SA in ER stress signalling and UPR has been almost fully characterised recently, the underlying mechanisms, interactions, and the potential molecular and physiological role of other defence-related phytohormones such as jasmonic acid (JA) has not yet been completely described [4,12,32,33]. Besides SA, JA also plays a crucial role during the plant-pathogen interactions and in resistance processes upon abiotic stressors [34][35][36][37][38][39].…”

Brassinosteroid Signaling Converges With Auxin-Mediated C3H17 to Regulate Xylem Formation in Populus

“…Biotin-labeled synthetic oligonucleotide was annealed with unlabeled oligonucleotides and then used as probes. A DNA protein-binding reaction was performed using a LightShift R Chemiluminescent EMSA Kit (Pierce) according to the previous description (Xu Z. et al, 2019). Briefly, the labeled DNA fragments were incubated for 25 min with 180 ng of the recombinant protein in binding buffer [10 mM Tris (pH 7.5), 1 mM DTT, 2.5% glycerol, 50 mM KCL, 10 mM MgCl 2 , 0.1% Nonidet P-40, and 50 ng/µL poly (dI-dC)].…”

Genome-wide identification and characterization ofSolanum tuberosum BiPgenes reveals the role of the promoter architecture in BiP gene diversity

“…Solanum species treated leaves with DTT or NaCl and carried out time course experiments to demonstrate that the transcriptional response of several UPR related genes including BiP can be seen as early as between 1 and 4 h after treatment using RT-qPCR [25][26][27][28][29][30] . For simplicity in this study, we infiltrated potato leaves with 2 mM DTT or 150 mM NaCl to induce ER stress and measured BiP transcript levels after 4 h of treatment 30,31 .…”