AUTHOR=Xu Zhen , Song Na , Ma Lan , Wu Jinsong 

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

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.00263

DOI=10.3389/fpls.2019.00263

ISSN=1664-462X

ABSTRACT=<p>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 <italic>Nicotiana attenuata</italic> resistance to necrotic fungal pathogen, <italic>Alternaria alternata</italic>. In this study, transcriptional levels of chaperone protein genes, including <italic>luminal binding protein</italic> (<italic>BiP</italic>), <italic>protein disulfide isomerase</italic> (<italic>PDI</italic>), <italic>calnexin 1-like</italic> (<italic>CNX 1-like</italic>), and <italic>calreticulin</italic> (<italic>CRT</italic>), and genes involved in IRE1-bZIP60 pathway, were all significantly induced in <italic>N. attenuata</italic> leaves after <italic>A. alternata</italic> inoculation. Silencing <italic>IRE1</italic> or <italic>bZIP60</italic> led to <italic>N. attenuata</italic> plants more susceptible to <italic>A. alternata</italic>, which were associated with reduced gene expressions of <italic>Feruloyl-CoA 6′-hydroxylase 1</italic> (<italic>F6′H1</italic>), 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 <italic>F6′H1 in vitro</italic>. JA signaling pathway is required for <italic>N. attenuata</italic> resistance to <italic>A. alternata</italic>. Interestingly, the fungus-elicited transcriptional levels of <italic>BiP</italic>, <italic>PDI</italic>, <italic>CNX 1-like</italic>, <italic>CRT</italic>, <italic>IRE1</italic>, and <italic>bZIP60</italic>(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 <italic>allene oxide synthase</italic> (<italic>AOS</italic>) and <italic>lipoxygenease 3</italic> (<italic>LOX3</italic>) were not affected in plants impaired with IRE1-bZIP60 pathway. Thus, it is concluded that IRE1-bZIP60 pathway is required for <italic>N. attenuata</italic> resistance to <italic>A. alternata</italic>, and JA signaling pathway plays an important role in the elicitation of chaperone protein genes and IRE1-bZIP60 pathway.</p>