S-nitrosylation may inhibit the activity of COP1 in plant photomorphogenesis.

Protein S-nitrosylation, which is defined by the covalent attachment of nitric oxide (NO) to the thiol group of cysteine residues, is known to play critical roles in plant development and stress responses. NO promotes seedling photomorphogenesis and NO emission is enhanced by light. However, the function of protein S-nitrosylation in plant photomorphogenesis is largely unknown. E3 ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) and transcription factor ELONGATED HYPOCOTYL 5 (HY5) antagonistically regulate seedling photomorphogenesis. COP1 inhibits plant photomorphogenesis by targeting photomorphogenic promoters like HY5 for 26S proteasome degradation. Here, we report that COP1 is S-nitrosylated in vitro. Mass spectrometry analyses revealed that two evolutionarily well conserved residues, cysteine 425 and cysteine 607, in the WD40 domain of COP1 are S-nitrosylated. S-nitrosylated glutathione (GSNO) is an important physiological NO donor for protein S-nitrosylation. The Arabidopsis (Arabidopsis thaliana) gsnor1-3 mutant, which accumulates higher level of GSNO, accumulated higher HY5 levels than wildtype (WT), indicating that COP1 activity is inhibited. Protein S-nitrosylation can be reversed by Thioredoxin-h5 (TRXh5) in plants. Indeed, COP1 interacts directly with TRXh5 and its close homolog TRXh3. Moreover, catalase 3 (CAT3) acts as a transnitrosylase that transfers NO to its target proteins like GSNO reductase (GSNOR). We found that CAT3 interacts with COP1 in plants. Taken together, our data indicate that the activity of COP1 is likely inhibited by NO via S-nitrosylation to promote the accumulation of HY5 and photomorphogenesis.

Perturbations in nitric oxide homeostasis promote Arabidopsis disease susceptibility towards Phytophthora parasitica.

Phytophthora species can infect hundreds of different plants, including many important crops, causing a number of agriculturally relevant diseases. A key feature of attempted pathogen infection is the rapid production of the redox active molecule nitric oxide (NO). However, the potential role(s) of NO in plant resistance against Phytophthora is relatively unexplored. Here we show that the level of NO accumulation is crucial for basal resistance in Arabidopsis against Phytophthora parasitica. Counterintuitively, both relatively low or relatively high NO accumulation leads to reduced resistance against P. parasitica. S-nitrosylation, the addition of a NO group to a protein cysteine thiol to form an S-nitrosothiol, is an important route for NO bioactivity and this process is regulated predominantly by S-nitrosoglutathione reductase 1 (GSNOR1). Loss-of-function mutations in GSNOR1 disable both salicylic acid accumulation and associated signalling, and also the production of reactive oxygen species, leading to susceptibility towards P. parasitica. Significantly, we also demonstrate that secreted proteins from P. parasitica can inhibit Arabidopsis GSNOR1 activity.

Persulfidation-based Modification of Cysteine Desulfhydrase and the NADPH Oxidase RBOHD Controls Guard Cell Abscisic Acid Signaling.

Hydrogen sulfide (H2S) is a gaseous signaling molecule that regulates diverse cellular signaling pathways through persulfidation, which involves the post-translational modification of specific Cys residues to form persulfides. However, the mechanisms that underlie this important redox-based modification remain poorly understood in higher plants. We have, therefore, analyzed how protein persulfidation acts as a specific and reversible signaling mechanism during the abscisic acid (ABA) response in Arabidopsis (Arabidopsis thaliana). Here we show that ABA stimulates the persulfidation of l-CYSTEINE DESULFHYDRASE1, an important endogenous H2S enzyme, at Cys44 and Cys205 in a redox-dependent manner. Moreover, sustainable H2S accumulation drives persulfidation of the NADPH oxidase RESPIRATORY BURST OXIDASE HOMOLOG PROTEIN D (RBOHD) at Cys825 and Cys890, enhancing its ability to produce reactive oxygen species. Physiologically, s-persulfidation-induced RBOHD activity is relevant to ABA-induced stomatal closure. Together, these processes form a negative feedback loop that fine-tunes guard cell redox homeostasis and ABA signaling. These findings not only expand our current knowledge of H2S function in the context of guard cell ABA signaling, but also demonstrate the presence of a rapid signal integration mechanism involving specific and reversible redox-based post-translational modifications that occur in response to changing environmental conditions.

Effects of abscisic acid, gibberellin, ethylene and their interactions on production of phenolic acids in salvia miltiorrhiza bunge hairy roots.

Salvia miltiorrhiza is one of the most important traditional Chinese medicinal plants because of its excellent performance in treating coronary heart disease. Phenolic acids mainly including caffeic acid, rosmarinic acid and salvianolic acid B are a group of active ingredients in S. miltiorrhiza. Abscisic acid (ABA), gibberellin (GA) and ethylene are three important phytohormones. In this study, effects of the three phytohormones and their interactions on phenolic production in S. miltiorrhiza hairy roots were investigated. The results showed that ABA, GA and ethylene were all effective to induce production of phenolic acids and increase activities of PAL and TAT in S. miltiorrhiza hairy roots. Effects of phytohormones were reversed by their biosynthetic inhibitors. Antagonistic actions between the three phytohormones played important roles in the biosynthesis of phenolic acids. GA signaling is necessary for ABA and ethylene-induced phenolic production. Yet, ABA and ethylene signaling is probably not necessary for GA3-induced phenolic production. The complex interactions of phytohormones help us reveal regulation mechanism of secondary metabolism and scale-up production of active ingredients in plants.