The diversity of substrates for plant respiration and how to optimize their use

Plant respiration is a foundational biological process with the potential to be optimized to improve crop yield. To understand and manipulate the outputs of respiration, the inputs of respiration-respiratory substrates-need to be probed in detail. Mitochondria house substrate catabolic pathways and respiratory machinery, so transport into and out of these organelles plays an important role in committing substrates to respiration. The large number of mitochondrial carriers and catabolic pathways that remain unidentified hinder this process and lead to confusion about the identity of direct and indirect respiratory substrates in plants. The sources and usage of respiratory substrates vary and are increasing found to be highly regulated based on cellular processes and environmental factors. This review covers the use of direct respiratory substrates following transport through mitochondrial carriers and catabolism under normal and stressed conditions. We suggest the introduction of enzymes not currently found in plant mitochondria to enable serine and acetate to be direct respiratory substrates in plants. We also compare respiratory substrates by assessing energetic yields, availability in cells, and their full or partial oxidation during cell catabolism. This information can assist in decisions to use synthetic biology approaches to alter the range of respiratory substrates in plants. As a result, respiration could be optimized by introducing, improving, or controlling specific mitochondrial transporters and mitochondrial catabolic pathways. Plant oxidation of respiratory substrates is regulated by mitochondrial transport and metabolic processes; modifications may enable oxidation of alternative substrates and improve efficiency.

Automated summary

Plant respiration is a vital process that can be enhanced to increase crop yield. To achieve this, a comprehensive understanding of respiratory substrates and their transport into and out of mitochondria is crucial. The identification of unidentified mitochondrial carriers and catabolic pathways is necessary to determine direct and indirect respiratory substrates. This review discusses the usage of direct respiratory substrates under normal and stressed conditions, suggesting the introduction of enzymes to enable new substrates and comparing them based on energetic yields and oxidation during cell catabolism. The information provided can guide the use of synthetic biology to optimize plant respiration.