Mitochondrial respiration is essential for photosynthesis-dependent ATP supply of the plant cytosol

Plants rely on solar energy to synthesize ATP and NADPH for photosynthetic carbon fixation. Since a substantial proportion of cellular ATP is consumed in the cytosol, photosynthesis-derived ATP needs to be supplied there. While the triose phosphate shuttle and mitochondrial respiration can both deliver ATP to the cytosol, the significance of the different mechanisms in vivo has been difficult to assess. Although mitochondrial respiration is essential in plants, whether this is due to heterotrophic bottlenecks during plant development or rather a need for respiration in photosynthetically active cells, has not been resolved. In this study, we examined in vivo changes of cytosolic ATP concentration in response to light, employing a biosensing strategy in the moss Physcomitrium patens . Our measurements revealed increased cytosolic ATP concentration caused by photosynthetic activity. Moss tissue depleted of respiratory complex I showed decreased cytosolic ATP accumulation, highlighting a critical role of mitochondrial respiration in light-dependent ATP supply of the cytosol. Consistently, targeting mitochondrial ATP production directly, through the construction of mutants deficient in mitochondrial ATPase (complex V), led to drastic growth reduction, despite only minor alterations in photosynthetic electron transport activity. Since P. patens is photoautotrophic throughout its development, we conclude that heterotrophic bottlenecks cannot account for the indispensable role of mitochondrial respiration in plants. Instead, our results offer compelling evidence that mitochondrial respiration is essential for ATP provision to the cytosol in actively photosynthesizing cells. Mitochondrial respiration provides metabolic integration, ensuring a reliable supply of cytosolic ATP essential for supporting plant growth and development. ### Competing Interest Statement The authors have declared no competing interest.