Strigolactone action in mitochondria triggers retrograde signaling for root growth modulation

Strigolactones (SL) are a new class of plant hormones with a broad range of roles in symbiosis, germination and developmental regulation. The well-characterized signaling pathway for SL involves the canonical signaling component MAX2. Here we identified a novel, MAX2-independent SL signaling mechanism, which initiates in mitochondria, signals to the nucleus and regulates root development. By a forward genetic approach, we identified the SL-insensitive pig1 mutant, which altered the kinetic properties of the mitochondrial pyruvate dehydrogenase complex. SL has an unknown target in mitochondria, where it uncouples respiration. This leads to metabolic aberrations, mitochondria-to-nucleus retrograde signaling upregulating transcription of mitochondrial dysfunction genes and downregulating auxin-regulated genes. SL-triggered mitochondrial uncoupling is communicated to the nucleus via cleavage and translocation of the ER-localized transcription factor ANAC017. These observations establish a novel mechanism for SL signaling emanating from mitochondria and regulating development. total RNA from 7-day old whole Arabidopsis thaliana seedlings, 3 biological replicates, rep1 of Col-0 Acetone and GR24 samples is the control for pig1 and PIN1-GFP samples, rep1 of Col-0 Acetone and GR24 samples is the control for anac017 samples