AUTHOR=Dogra Vivek , Duan Jianli , Lee Keun Pyo , Lv Shanshan , Liu Renyi , Kim Chanhong 

TITLE=FtsH2-Dependent Proteolysis of EXECUTER1 Is Essential in Mediating Singlet Oxygen-Triggered Retrograde Signaling in Arabidopsis thaliana

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.01145

DOI=10.3389/fpls.2017.01145

ISSN=1664-462X

ABSTRACT=<p>Photosystem II reaction center (PSII RC) and light-harvesting complex inevitably generate highly reactive singlet oxygen (<sup>1</sup>O<sub>2</sub>) that can impose photo-oxidative damage, especially when the rate of generation exceeds the rate of detoxification. Besides being toxic, <sup>1</sup>O<sub>2</sub> has also been ascribed to trigger retrograde signaling, which leads to nuclear gene expression changes. Two distinctive molecular components appear to regulate <sup>1</sup>O<sub>2</sub> signaling: a volatile signaling molecule β-cyclocitral (β-CC) generated upon oxidation of β-carotene by <sup>1</sup>O<sub>2</sub> in PSII RC assembled in grana core, and a thylakoid membrane-bound FtsH2 metalloprotease that promotes <sup>1</sup>O<sub>2</sub>-triggered signaling through the proteolysis of EXECUTER1 (EX1) proteins associated with PSII in grana margin. The role of FtsH2 protease in <sup>1</sup>O<sub>2</sub> signaling was established recently in the conditional <italic>fluorescent</italic> (<italic>flu</italic>) mutant of <italic>Arabidopsis thaliana</italic> that generates <sup>1</sup>O<sub>2</sub> upon dark-to-light shift. The <italic>flu</italic> mutant lacking functional FtsH2 significantly impairs <sup>1</sup>O<sub>2</sub>-triggered and EX1-mediated cell death. In the present study, the role of FtsH2 in the induction of <sup>1</sup>O<sub>2</sub> signaling was further clarified by analyzing the FtsH2-dependent nuclear gene expression changes in the <italic>flu</italic> mutant. Genome-wide transcriptome analysis showed that the inactivation of FtsH2 repressed the majority (85%) of the EX1-dependent <sup>1</sup>O<sub>2</sub>-responsive genes (SORGs), providing direct connection between FtsH2-mediated EX1 degradation and <sup>1</sup>O<sub>2</sub>-triggered gene expression changes. Furthermore, the overlap between β-CC-induced genes and EX1-FtsH2-dependent genes was very limited, further supporting the coexistence of two distinctive <sup>1</sup>O<sub>2</sub> signaling pathways.</p>