Coordinated regulation of the mitochondrial retrograde response by circadian clock regulators and ANAC017

Mitochondrial retrograde signaling (MRS) supports photosynthetic function under a variety of conditions. Induction of mitochondrial dysfunction with myxothiazol (a specific inhibitor of the mitochondrial bc1 com-plex) or antimycin A (an inhibitor of the mitochondrial bc1 complex and cyclic electron transport in the chlo-roplast under light conditions) in the light and dark revealed diurnal control of MRS. This was evidenced by (1) significantly enhanced binding of ANAC017 to promoters in the light compared with the dark in Arabi-dopsis plants treated with myxothiazol (but not antimycin A), (2) overlap in the experimentally determined binding sites for ANAC017 and circadian clock regulators in the promoters of ANAC013 and AOX1a, (3) a diurnal expression pattern for ANAC017 and transcription factors it regulates, (4) altered expression of ANAC017-regulated genes in circadian clock mutants with and without myxothiazol treatment, and (5) a decrease in the magnitude of LHY and CCA1 expression in an ANAC017-overexpressing line and pro-tein-protein interaction between ANAC017 and PIF4. This study also shows a large difference in transcrip-tome responses to antimycin A and myxothiazol in the dark: these responses are ANAC017 independent, observed in shoots and roots, similar to biotic challenge and salicylic acid responses, and involve ERF and ZAT transcription factors. This suggests that antimycin A treatment stimulates a second MRS pathway that is mediated or converges with salicylic acid signaling and provides a merging point with chloroplast retrograde signaling.

Automated summary

Mitochondrial retrograde signaling (MRS) regulates photosynthetic function under different conditions by controlling the binding of ANAC017 to promoters and the expression of related transcription factors. The study also found that there is a separate MRS pathway stimulated by antimycin A treatment, which intersects with salicylic acid signaling and chloroplast retrograde signaling. Additionally, the transcriptional responses to antimycin A and myxothiazol in the dark are ANAC017 independent and involve ERF and ZAT transcription factors, resembling biotic challenge and salicylic acid responses.