Redox modulation of Rubisco conformation and activity through its cysteine residues

Differential modulation of S-nitrosoproteome of Brassica juncea by low temperature: change in S-nitrosylation of Rubisco is responsible for the inactivation of its carboxylase activity

Nitric oxide (NO), a new addition to plant hormones, affects numerous processes in planta. It is produced as a part of stress response, but its signaling is poorly understood. S-nitrosylation, a PTM, is currently the most investigated modification of NO. Recent studies indicate significant modulation of metabolome by S-nitrosylation, as the identified targets span major metabolic pathways and regulatory proteins. Identification of S-nitrosylation targets is necessary to understand NO signaling. By combining biotin switch technique and MS, 20 S-nitrosylated proteins including four novel ones were identified from Brassica juncea. Further, to know if the abiotic stress-induced NO evolution contributes to S-nitrosothiols (SNO), the cellular NO reservoirs, SNO content was measured by Saville method. Low temperature (LT)-stress resulted in highest (1.4-fold) SNO formation followed by drought, high temperature and salinity. LT induced differentially nitrosylated proteins were identified as photosynthetic, plant defense related, glycolytic and signaling associated. Interestingly, both the subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) showed an increase as well as a decrease in nitrosylation by LT. Inactivation of Rubisco carboxylase by LT is well documented but the mechanism is not known. Here, we show that LT-induced S-nitrosylation is responsible for significant ( approximately 40%) inactivation of Rubisco. This in turn could explain cold stress-induced photosynthetic inhibition.

Protein nitration during defense response in Arabidopsis thaliana

Nitric oxide and reactive oxygen species play a key role in the plant hypersensitive disease resistance response, and protein tyrosine nitration is emerging as an important mechanism of their co-operative interaction. Up to now, the proteins targeted by this post-translational modification in plants are still totally unknown. In this study, we analyzed for the first time proteins undergoing nitration during the hypersensitive response by analyzing via 1D- and 2D-western blot the protein extracts from Arabidopsis thaliana plants challenged with an avirulent bacterial pathogen (Pseudomonas syringae pv. Tomato). We show that the plant disease resistance response is correlated with a modulation of nitration of proteins involved in important cellular process, such as photosynthesis, glycolysis and nitrate assimilation. These findings shed new light on the signaling functions of nitric oxide and reactive oxygen species, paving the way on studies on the role of this post-translational modification in plants.

Redox regulation in photosynthetic organisms: signaling, acclimation, and practical implications

Reactive oxygen species (ROS) have multifaceted roles in the orchestration of plant gene expression and gene-product regulation. Cellular redox homeostasis is considered to be an "integrator" of information from metabolism and the environment controlling plant growth and acclimation responses, as well as cell suicide events. The different ROS forms influence gene expression in specific and sometimes antagonistic ways. Low molecular antioxidants (e.g., ascorbate, glutathione) serve not only to limit the lifetime of the ROS signals but also to participate in an extensive range of other redox signaling and regulatory functions. In contrast to the low molecular weight antioxidants, the "redox" states of components involved in photosynthesis such as plastoquinone show rapid and often transient shifts in response to changes in light and other environmental signals. Whereas both types of "redox regulation" are intimately linked through the thioredoxin, peroxiredoxin, and pyridine nucleotide pools, they also act independently of each other to achieve overall energy balance between energy-producing and energy-utilizing pathways. This review focuses on current knowledge of the pathways of redox regulation, with discussion of the somewhat juxtaposed hypotheses of "oxidative damage" versus "oxidative signaling," within the wider context of physiological function, from plant cell biology to potential applications.