Photorespiration Regulates Carbon–Nitrogen Metabolism by Magnesium Chelatase D Subunit in Rice

Abstract

The growth and development of plants are dependent on the interaction between carbon and nitrogen metabolism. Essential information about the metabolic regulation of carbon-nitrogen metabolism is still lacking, such as possible interactions among nitrogen metabolism, photosynthesis, and photorespiration. This study shows that higher photorespiration consumes more CO₂ fixed by photosynthesis, making the high photosynthetic efficiency mutant fail to increase production. In order to clarify the effects of photosynthesis and photorespiration on carbon and nitrogen metabolism in high photosynthetic efficiency mutant, a yellow-green leaf mutant (<i>ygl53</i>) was isolated from rice (<i>Oryza sativa</i> L.). Its chlorophyll (Chl) content decreased, but chloroplast development was not affected. Genetic analysis demonstrated that <i>YGL53</i> encodes the magnesium chelatase D subunit (ChlD). The <i>ygl53</i> mutant showed an increased net assimilation rate (An) and electron transport flux efficiency and catalase (CAT) activity, and it also had a higher photorespiration rate (Pr), lower H₂O₂, and reduced nitrogen uptake efficiency (NUpE); however, there was no loss in yield. The higher activities of glutamate synthase (GOGAT) and glutamine synthetase (GS) ensure the α-ketoglutaric acid (2-OG) and ammonia (NH₃) availabilities, which are produced from photorespiration in the <i>ygl53</i> mutant. These have an important function for carbon and nitrogen metabolism homeostasis in <i>ygl53</i>. Further analysis indicated that the energy and substances derived from carbon metabolism supplemented nitrogen metabolism in the form of photorespiration to ensure its normal development when the An of photosynthesis was increased in the <i>ygl53</i> mutant with reduced NUpE.