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Nitric oxide in plant-pathogen interactions

Nitric oxide (NO) is a highly reactive molecule that rapidly diffuses and permeates cell membranes. In animals, NO is implicated in a number of diverse physiological processes such as neurotransmission, vascular smooth muscle relaxation, and platelet inhibition. It may have beneficial effects, for example as a messenger in immune responses, but is also potentially toxic when the antioxidant system is weak and an excess of reactive oxygen intermediates (ROI) accumuates. During the last few years NO has been detected also in several plant species, and the increasing number of reports on its function in plants have implicated NO as an important effector of growth, development, and defense. The broad chemistry of NO involves an array of interrelated redox forms with different chemical reactivities, and numerous potential targets of NO action exist in plants. NO signaling functions depend on its reactivity and ROI are key modulators of NO in triggering cell death, although through mechanisms different from those commonly observed in animals    

Between 1995 and 1998, in the lab of ChrisLamb at the Salk Institute we made pioneering work towards the discovery of NO function during the plant hypersensitive disease resistance response. We found that during the hypersensitive response plant cells accumulate NO, which co-operates with reactive oxygen species in the induction of hypersensitive cell death, and functions independently of such intermediates in the induction of defence related genes. We then demonstrated that the rates of production and dismutation of O2- generated during the oxidative burst play a crucial role in the modulation and integration of NO/H2O2 signalling in the hypersensitive response.

Due to the many possible mechanisms of NO action, a clear picture of its involvement in plant resistance to pathogens was far from being achieved. I have then dedicated about 10 years to the characterization and modulation of the signal transduction pathways leading to the hypersensitive disease resistance response. My lab went in deep in the analysis of genes involved in the hypersensitive cell death and in the establishment of disease resistance whose expression is under control of NO. 
   
We also focussed on the mechanisms regulating NO level in plant, and on the identification and characterization of signalling mechanisms that operate downstream of NO accumulation. In particular, we analysed the occurrence of NO-dependent posttranslational modifications of proteins (S-nitrosylation and Tyr-nitration) to clarify their biological function and to understand their functional consequences in physiological and pathophysiological conditions.

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