Interplay between ROS and RNS in tobacco response to cryptogein

Cryptogein is a 10 kDa protein secreted by Phytophthora cryptogea triggering a systemic acquired resistance as well as a hypersensitive response in tobacco. The signaling events induced by cryptogein have been studied intensively and include, production of reactive oxygen species and nitric oxide. While the origin for NO production is still unknown, NtRBOHD has been reported as the primary source for O2•─ and derived H2O2. In this study, we investigated the cross-talks between NO and ROS in cryptogein signaling. Using antisense tobacco Xanthi suspension cells impaired in NtRBOHD expression as well as a pharmacological-based approach, we showed that NO synthesis is partly regulated through a ROS-dependent mechanism. Conversely, scavenging of NO leads to a slight increase of ROS accumulation, suggesting that NO might regulate its pool by interaction with O2•─. We further defined NO as a major determinant of cryptogein-induced cell death. To better assess the role of NO in tobacco response to cryptogein, a search for NO-responsive genes was performed. Fifteen NO-dependent genes of interest were selected. Expression of some of them was regulated by H2O2 either, reinforcing the hypothesis of shared signaling pathways for these two reactive species