Role of aconitase in plant stress response and signaling

Mitochondria are the centres of carbon and energy metabolism in cells and are functionally integrated with other organelles. Under environmental stress, disturbances in organellar functions trigger stress signals that activate the necessary metabolic responses and maintain cell redox homeostasis. The tricarboxylic acid cycle enzyme aconitase has emerged as a key component in stress-induced organellar signalling and a regulator of metabolic and redox balance in photosynthetic organisms. Aconitase mediates mitochondrial and chloroplast retrograde signalling and contributes to the activation of the alternative oxidase (AOX) pathway in mitochondria. Aconitase-driven citrate metabolism plays a crucial role in providing reducing equivalents and metabolic precursors for cytosolic nitrogen metabolism and biosynthetic pathways relevant for stress acclimation. Besides its enzymatic activity, aconitase has a non-canonical function as it is a post-transcriptional regulator of specific gene transcripts. The varied functions of aconitase under stress are facilitated by the regulation of specific aconitase isoforms at multiple levels. This review discusses the emerging role of aconitase as a central regulator of stress responses and signalling in photosynthetic organisms.