‘Breathing Out’ under Heat Stress—Respiratory Control of Crop Yield under High Temperature

Respiration and photosynthesis are indispensable plant metabolic processes that are affected by elevated temperatures leading to disruption of the carbon economy of the plants. Increasing global temperatures impose yield penalties in major staple crops that are attributed to increased respiratory carbon loss, through higher maintenance respiration resulting in a shortage of non-structural carbohydrates and an increase in metabolic processes like protein turnover and maintenance of ion concentration gradients. At a cellular level, warmer temperatures lead to mitochondrial swelling as well as downregulation of respiration by increasing the adenosine triphosphate:adenosine diphosphate (ATP:ADP) ratio, the abscisic acid-mediated reduction in ATP transfer to the cytosol, and the disturbance in a concentration gradient of tricarboxylic acid (TCA) cycle intermediates, as well as increasing lipid peroxidation in mitochondrial membranes and cytochrome c release to trigger programmed cell death. In this review, we discuss the mechanistic insight into the heat stress-induced mitochondrial dysfunction that controls dark respiration in plants. Furthermore, the role of hormones in regulating the network of processes that are involved in retrograde signaling is highlighted. We also propose different strategies to reduce carbon loss under high temperature, e.g., selecting genotypes with low respiration rates and using genome editing tools to target the carbon-consuming pathways by replacing, relocating, or rescheduling the metabolic activities