Mitochondrial signalling is critical for acclimation and adaptation to flooding in Arabidopsis thaliana

Mitochondria have critical functions in the acclimation to abiotic and biotic stresses. Adverse environmental conditions lead to increased demands in energy supply and metabolic intermediates which are provided by mitochondrial ATP production and the TCA cycle. Mitochondria also play a role as stress sensors to adjust nuclear gene expression via retrograde signalling with the transcription factor ANAC017 and the kinase CDKE1 key components to integrate various signals into this pathway. To determine the importance of mitochondria as sensors of stress and their contribution in the tolerance to adverse growth conditions, a comparative phenotypical, physiological and transcriptomic characterization of Arabidopsis mitochondrial signalling mutants (cdke1/rao1 and anac017/rao2) and a set of contrasting accessions was performed after applying the complex compound stress of submergence. Our results showed that impaired mitochondrial retrograde signalling leads to increased sensitivity to the stress treatments. The multi‐factorial approach identified a network of 702 co‐expressed genes, including several WRKY transcription factors, overlapping in the transcriptional responses in the mitochondrial signalling mutants and stress‐sensitive accessions. Functional characterization of two WRKY transcription factors (WRKY40 and WRKY45), using both knock‐out and over‐expressing lines, confirmed their role in conferring tolerance to submergence. Together the results revealed that acclimation to submergence is dependent on mitochondrial retrograde signalling and underlying transcriptional re‐programming is used as an adaptation mechanism.