Chloroplast-generated reactive oxygen species contribute decisively to localised cell death during a plant-microorganism nonhost interaction

ZURBRIGGEN M; TOGNETTI V; VALLE E; HAJIREZAEI MR; CARRILLO N

Águas de Lindóia, São Paulo, Brazil

Congreso; XXXVII Annual Meeting of the Brazilian Society for Biochemistry and Molecular Biology (SBBq), and the XI Congress of the Panamerican Association for Biochemistry and Molecular Biology (PABMB); 2008

Brazilian Society for Biochemistry and Molecular Biology (SBBq), and the XI Congress of the Panamerican Association for Biochemistry and Molecular Biology (PABMB)

Attempted infection of plants by pathogenic microorganisms elicits a complex battery of defensive responses. In many nonhost and incompatible host interactions, they include induction of defence-related genes and a form of localised cell death to restrict further 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. To gain further insights into the mechanism of the HR and the role played by ROS in its activation, we evaluated the response of tobacco plants expressing a cyanobacterial flavodoxin during challenge with Xanthomonas campestris pv vesicatoria, a nonhost pathogen. Flavodoxin is an electron shuttle present in prokaryotes and some algae that, when expressed in chloroplasts, acts as a general antioxidant avoiding ROS formation and conferring tolerance to various sources of abiotic stress. Infiltration of wild-type (WT) leaves with Xcv resulted in the appearance of necrotic lesions typical of the HR, that were almost entirely prevented in the transformants. Metabolic routes inhibited by pathogen infection were preserved in transgenic plants, as reflected by rates of photosynthesis and respiration, normal levels of amino acids and accumulation of reduced antioxidants. Other aspects of the HR such as induction of pathogenesis-related genes and jasmonic acid synthesis proceeded as in WT plants. The results indicate that a combination of oxidants and/or the chloroplast redox status are important for development of cell death upon pathogen infection.