Chloroplast-generated reactive oxygen species play a major role in localized cell death during the non-host interaction between tobacco and Xanthomonas campestris pv. vesicatoria

• Published in: The Plant journal : for cell and molecular biology 2009-12, Vol.60 (6), p.962-973
• Main Authors: Zurbriggen, Matias D, Carrillo, Néstor, Tognetti, Vanesa B, Melzer, Michael, Peisker, Martin, Hause, Bettina, Hajirezaei, Mohammad-Reza
• Format: Article
• Language: English
• Subjects: Apoptosis; Cell Death; Chloroplasts; Chloroplasts - metabolism; Cyclopentanes - metabolism; flavodoxin; Flavodoxin - metabolism; Gene expression; Gene Expression Regulation, Plant; Nicotiana - genetics; Nicotiana - metabolism; Nicotiana - microbiology; non-host resistance; oxidative stress; Oxygen; Oxylipins - metabolism; Plant biology; Plant Diseases; Plant Leaves - genetics; Plant Leaves - metabolism; Plant Leaves - microbiology; plant-pathogen interactions; Plants, Genetically Modified - genetics; Plants, Genetically Modified - metabolism; Plants, Genetically Modified - microbiology; reactive oxygen species; Reactive Oxygen Species - metabolism; RNA, Plant - genetics; Salicylic Acid - metabolism; Tobacco; Xanthomonas campestris - physiology
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313x.2009.04010.x

Attempted infection of plants by pathogens elicits a complex defensive response. In many non-host and incompatible host interactions it includes the induction of defence-associated genes and a form of localized cell death (LCD), purportedly designed to restrict pathogen advance, collectively known as the hypersensitive response (HR). It is preceded by an oxidative burst, generating reactive oxygen species (ROS) that are proposed to cue subsequent deployment of the HR, although neither the origin nor the precise role played by ROS in the execution of this response are completely understood. We used tobacco plants expressing cyanobacterial flavodoxin to address these questions. Flavodoxin is an electron shuttle present in prokaryotes and algae that, when expressed in chloroplasts, specifically prevents ROS formation in plastids during abiotic stress episodes. Infiltration of tobacco wild-type leaves with high titres of Xanthomonas campestris pv. vesicatoria (Xcv), a non-host pathogen, resulted in ROS accumulation in chloroplasts, followed by the appearance of localized lesions typical of the HR. In contrast, chloroplast ROS build-up and LCD were significantly reduced in Xcv-inoculated plants expressing plastid-targeted flavodoxin. Metabolic routes normally inhibited by pathogens were protected in the transformants, whereas other aspects of the HR, including the induction of defence-associated genes and synthesis of salicylic and jasmonic acid, proceeded as in inoculated wild-type plants. Therefore, ROS generated in chloroplasts during this non-host interaction are essential for the progress of LCD, but do not contribute to the induction of pathogenesis-related genes or other signalling components of the response.