Down-regulation of free riboflavin content induces hydrogen peroxide and a pathogen defense in Arabidopsis

Abstract

Riboflavin mediates many bioprocesses associated with the generation of hydrogen peroxide (H₂O₂), a cellular signal that regulates defense responses in plants. Although plants can synthesize riboflavin, the levels vary widely in different organs and during different stages of development, indicating that changes in riboflavin levels may have physiological effects. Here, we show that changing riboflavin content affects H₂O₂ accumulation and a pathogen defense in Arabidopsis thaliana. Leaf content of free riboflavin was modulated by ectopic expression of the turtle gene encoding riboflavin-binding protein (RfBP). The RfBP-expressing Arabidopsis thaliana (REAT) plants produced the RfBP protein that possessed riboflavin-binding activity. Compared with the wild-type plant, several tested REAT lines had >70% less flavins of free form. This change accompanied an elevation in the level of H₂O₂ and an enhancement of plant resistance to a bacterial pathogen. All the observed REAT characters were eliminated due to RfBP silencing (RfBPi) under REAT background. When an H₂O₂ scavenger was applied, H₂O₂ level declined in all the plants, and REAT no longer exhibited the phenotype of resistance enhancement. However, treatment with an NADPH oxidase inhibitor diminished H₂O₂ content and pathogen defense in wild-type and RfBPi but not in REAT. Our results suggest that the intrinsic down-regulation of free flavins is responsible for NADPH oxidase-independent H₂O₂ accumulation and the pathogen defense.

Plant Aquaporin AtPIP1;4 Links Apoplastic H2O2 Induction to Disease Immunity Pathways

“…To (Ashtamker et al, 2007;Rhee et al, 2010;Deng et al, 2011;Sang et al, 2012). By laser confocal microscopy performed on leaves 1 hpi, we found that AUR and AR probing well visualized the H 2 O 2 present in the apoplast and cytoplasm, respectively (Fig.…”

Plant amino acid-derived vitamins: biosynthesis and function

“…Riboflavin-deficient tobacco plants present compromised radical production (ROS and reactive nitrogen species) and hypersensitive cell death response (Asai et al 2010), while increased levels of riboflavin act as an elicitor of SAR (Dong and Beer 2000) via the induction of ROS and hormonal signaling transduction pathways, promoting the phenylpropanoid pathway and phenolics accumulation Taheri and Tarighi 2011;Li et al 2012b). Curiously, diminishing free flavins (through the ectopic expression of a flavin-binding protein) also elevates the levels of H 2 O 2 enhancing plant resistance to bacterial pathogens (Deng et al 2011).…”

Downregulation of leaf flavin content induces early flowering and photoperiod gene expression in Arabidopsis

“…Foliar application of riboflavin increases the intrinsic concentrations of all flavins (riboflavin, FMN, and FAD), alters cellular redox, and induces defense responses to pathogens [6–10]. The foliar flavin content can be also modulated by transgenic expression of the turtle ( Trionyx sinensis japonicus ) gene encoding riboflavin-binding protein (RfBP) [11]. The protein contains a nitroxyl-terminal (N-terminal) ligand-binding domain, which is implicated in molecular interactions, and a carboxyl-terminal (C-terminal) phosphorylated domain, which accommodates the riboflavin molecule [12–15].…”

“…The protein contains a nitroxyl-terminal (N-terminal) ligand-binding domain, which is implicated in molecular interactions, and a carboxyl-terminal (C-terminal) phosphorylated domain, which accommodates the riboflavin molecule [12–15]. In the RfBP -expressing (RfBP + ) Arabidopsis thaliana line, the RfBP protein localizes to chloroplasts, binds with riboflavin to decrease free flavin concentrations in leaves, and enhances the plant resistance to diseases [11]. The induction of disease resistance accompanies elevated cytosolic levels of hydrogen peroxide (H 2 O 2 ), a cellular signal that can regulate defense responses [7,10,11,16].…”

“…In the RfBP -expressing (RfBP + ) Arabidopsis thaliana line, the RfBP protein localizes to chloroplasts, binds with riboflavin to decrease free flavin concentrations in leaves, and enhances the plant resistance to diseases [11]. The induction of disease resistance accompanies elevated cytosolic levels of hydrogen peroxide (H 2 O 2 ), a cellular signal that can regulate defense responses [7,10,11,16]. All of these RfBP-conferred responses can be eliminated by nullifying RfBP expression and abolishing production of the RfBP protein.…”