Hydrogen Peroxide Generation by the Pepper Extracellular Peroxidase CaPO2 Activates Local and Systemic Cell Death and Defense Response to Bacterial Pathogens

Abstract

Reactive oxygen species (ROS) are responsible for mediating cellular defense responses in plants. Controversy has existed over the origin of ROS in plant defense. We have isolated a novel extracellular peroxidase gene, CaPO2, from pepper (Capsicum annuum). Local or systemic expression of CaPO2 is induced in pepper by avirulent Xanthomonas campestris pv vesicatoria (Xcv) infection. We examined the function of the CaPO2 gene in plant defense using the virus-induced gene silencing technique and gain-of-function transgenic plants. CaPO2-silenced pepper plants were highly susceptible to Xcv infection. Virus-induced gene silencing of the CaPO2 gene also compromised hydrogen peroxide (H 2 O 2 ) accumulation and hypersensitive cell death in leaves, both locally and systemically, during avirulent Xcv infection. In contrast, overexpression of CaPO2 in Arabidopsis (Arabidopsis thaliana) conferred enhanced disease resistance accompanied by cell death, H 2 O 2 accumulation, and PR gene induction. In CaPO2-overexpression Arabidopsis leaves infected by Pseudomonas syringae pv tomato, H 2 O 2 generation was sensitive to potassium cyanide (a peroxidase inhibitor) but insensitive to diphenylene iodonium (an NADPH oxidase inhibitor), suggesting that H 2 O 2 generation depends on peroxidase in Arabidopsis. Together, these results indicate that the CaPO2 peroxidase is involved in ROS generation, both locally and systemically, to activate cell death and PR gene induction during the defense response to pathogen invasion.

Reactive oxygen species and plant resistance to fungal pathogens

“…ROS formation dependent on an apoplastic peroxidase was later confirmed in other plants (bean, Arabidopsis, pepper, lettuce, cotton) (Bestwick et al, 1998;Bindschedler et al, 2006;Bolwell, 1999;Choi et al, 2007;Martinez et al, 1998). The relevance of apoplastic peroxidase was explored in A. thaliana expressing an antisense construct of the heme-containing cell-wall-bound class III peroxidase FBP1 of French bean.…”

Dual Roles of Reactive Oxygen Species and NADPH Oxidase RBOHD in an Arabidopsis-Alternaria Pathosystem

“…Newly generated knockout mutants or sense and antisense transgenic lines provided impressive genetic evidence for the significance of these enzymes in the response of plants to pathogens. Cell wall peroxidases have been reported to function as resistance factors conferring defense to plants against various invading pathogens and also as positive regulators of cell death (Bindschedler et al, 2006;Choi et al, 2007). Interestingly, results about the role of NADPH oxidases in the interaction of plants with invading pathogens have presented a less uniform, more complex picture.…”

Unraveling the Tapestry of Networks Involving Reactive Oxygen Species in Plants

“…With a diverse arsenal of ROS-generating enzymes, such as the plant orthologs of the respiratory burst NADPH oxidases (RBOHs), plant cells, like mammalian cells, can initiate and most probably amplify ROS production for the purpose of ROS signaling. A newly identified extracellular peroxidase and two type III peroxidases play an active role in H 2 O 2 production and subsequent cell death in the local and systemic response to pathogen attack (Bindschedler et al, 2006;Choi et al, 2007). During pathogenesis or wounding, ROS production is mainly apoplastic, whereas during salt stress ROS also can be produced from internalized membranes (endosomes) by NADPH oxidase in a phosphatidylinositol 3-kinase-dependent manner (Leshem et al, 2006(Leshem et al, , 2007.…”