Rice NADP-dependent malate dehydrogenase gene OsMDH8.2 is involved in heat tolerance

Convergent and divergent evolution lead to plants with stronger adaptability to higher temperatures, thus averting crop biomass yield reductions. NADP-dependent malate dehydrogenase (NADP-MDH) is a redox-regulated enzyme that catalyzes the reversible reduction of oxaloacetate to malate. The sole NADP-MDH gene in rice, OsMDH8.2, is expressed in mesophyll cells of photosynthetic organs and various sink tissues. However, it is unknown whether NADP-MDH functions in heat stress in rice. We characterized a transgenic OsMDH8.2 overexpression line under thermal stress treatment (40 °C). The transgenic line exhibited better adaptability to heat stress than the wild type; it better maintained biomass and a lower surface temperature through stomatal closure, and photosynthetic activity was less affected. OsMDH8.2 was found to affect peroxidase activity by reducing the hydrogen peroxide content in flag leaves after 3 and 5 days of thermal stress. Analysis results of OsMDH8.2 knockout lines confirmed that OsMDH8.2 contributes to heat tolerance. Transcriptome and metabolome analyses demonstrated that OsMDH8.2 plays a key role in energy homeostasis by reducing tricarboxylic acid cycle activity while inducing the glyoxylate cycle to produce more energy, and by regulating amino acid metabolism to rescue heat-stress damage. Collectively, these results suggest that OsMDH8.2 enhances glyoxylate cycle efficiency, resulting in lower carbon dioxide release into the environment through stomatal closure, providing an excellent strategy for improving plant heat tolerance through genetic engineering.