The Arabidopsis Mitochondrial Nucleoid-Associated Protein WHIRLY2 is Required for a Proper Response to Salt Stress

: In the last years, plant organelles have emerged as central coordinators of responses to internal and external stimuli which can induce stress. Mitochondria play a fundamental role as stress sensors being part of a complex communication network between the organelles and nucleus. Among the different environmental stresses, salt stress poses a significant challenge and requires efficient signaling and protective mechanisms. By using the why2 T-DNA insertion mutant and a novel knockout mutant prepared by CRISPR Cas9 mediated genome editing, this study revealed that WHIRLY2 is crucial in protecting mitochondrial DNA (mtDNA) integrity during salt stress. Loss-of-function mutants show an enhanced sensitivity to salt stress. The disruption of WHIRLY2 causes the impairement of mtDNA repair that results in the accumulation of aberrant recombination products, coinciding with severe alterations in nucleoid integrity and overall mitochondria morphology besides a compromised redox-dependent response and mis-regulation of antioxidant enzymes. The results of this study revealed that WHIRLY2 mediated structural features in mitochondria (nucleoid compactness, cristae) are important for an effective response to salt stress.