Light-dependent expression of flg22-induced defense genes in Arabidopsis.

Satoshi Sano,Takashi Shiina,Koji Shimotani,Daisuke Tojo,I Nengah Suwastika,Kanako Yamasaki,Hironari Nomura,Masa H Sato,Mayu Aoyama,Kana Nakai

doi:10.3389/fpls.2014.00531

Abstract

Chloroplasts have been reported to generate retrograde immune signals that activate defense gene expression in the nucleus. However, the roles of light and photosynthesis in plant immunity remain largely elusive. In this study, we evaluated the effects of light on the expression of defense genes induced by flg22, a peptide derived from bacterial flagellins which acts as a potent elicitor in plants. Whole-transcriptome analysis of flg22-treated Arabidopsis thaliana seedlings under light and dark conditions for 30 min revealed that a number of (30%) genes strongly induced by flg22 (>4.0) require light for their rapid expression, whereas flg22-repressed genes include a significant number of genes that are down-regulated by light. Furthermore, light is responsible for the flg22-induced accumulation of salicylic acid (SA), indicating that light is indispensable for basal defense responses in plants. To elucidate the role of photosynthesis in defense, we further examined flg22-induced defense gene expression in the presence of specific inhibitors of photosynthetic electron transport: 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-benzoquinone (DBMIB). Light-dependent expression of defense genes was largely suppressed by DBMIB, but only partially suppressed by DCMU. These findings suggest that photosynthetic electron flow plays a role in controlling the light-dependent expression of flg22-inducible defense genes.

Highlights

Over the course of their evolution, plants have developed defense systems against a broad-spectrum of pathogens
LIGHT-DEPENDENT EXPRESSION OF flg22-INDUCED DEFENSE GENES To identify genes rapidly responsive to flg22 whose expression is controlled by light, we performed microarray analysis of lightand dark-dependent gene expression in Arabidopsis seedlings treated with flg22 for 30 min
We previously demonstrated that the chloroplast Ca2+-binding protein CAS plays a role in flg22-induced immune responses through retrograde signals originating in chloroplasts to regulate defense gene expression in the nucleus (Nomura et al, 2012)

Summary

Introduction

Over the course of their evolution, plants have developed defense systems against a broad-spectrum of pathogens. Plant cells recognize pathogens through pattern-recognition receptors (PRRs) that recognize common features of microbial pathogens, termed pathogen-associated molecular patterns (PAMPs). The recognition of PAMPs by PRRs rapidly initiates downstream signaling events that result in the activation of an array of basal defense responses (PAMP-triggered immunity, PTI; Chisholm et al, 2006; Göhre and Robatzek, 2008). Effectortriggered immunity (ETI) induces cell death at infection sites to enclose the spread of pathogens, a process known as the hypersensitive reaction (HR). There are two distinct pathways that produce SA from chorismate in plants: the isochorismate (ICS) pathway in chloroplasts and the phenylalanine ammonia-lyase (PAL) pathway in the cytoplasm. It was demonstrated that SA is synthesized in chloroplasts via the ICS pathway, but not in the cytoplasm, in Arabidopsis (Fragnière et al, 2011)

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