Photosynthesis provides food, fibre and fuel that support our society; understanding the mechanisms controlling dynamic changes in this process helps identify new options to improve photosynthesis. Photosynthesis shows diel changes, which have been largely attributed to external light/dark conditions, as well as internal gene expression and the post-translational modification of critical enzymes. Here we report diel fluctuations of magnesium (Mg) in rice (Oryza sativa) chloroplasts, which may function as a rhythm regulator contributing to the post-translational regulation of photosynthetic CO₂ assimilation in rice. We found that a chloroplast-localized Mg²⁺ transporter gene, OsMGT3, which is rhythmically expressed in leaf mesophyll cells, partly modulates Mg fluctuations in rice chloroplasts. Knockout of OsMGT3 substantially reduced Mg²⁺ uptake, as well as the amplitude of free Mg²⁺ fluctuations in chloroplasts, which was closely associated with a decrease in ribulose 1,5-bisphosphate carboxylase activity in vivo and a consequent decline in the photosynthetic rate. In addition, the mesophyll-specific overexpression of OsMGT3 remarkably improved photosynthetic efficiency and growth performance in rice. Taken together, these observations demonstrate that OsMGT3-dependent diel Mg fluctuations in chloroplasts may contribute to Mg-dependent enzyme activities for photosynthesis over the daily cycle. Enhancing Mg²⁺ input to chloroplasts could be a potential approach to improving photosynthetic efficiency in plants.

光合作用提供支持我们社会的食物，纤维和燃料；了解此过程中控制动态变化的机制有助于发现改善光合作用的新选择。光合作用显示出diel变化，这主要归因于外部光照/黑暗条件，以及内部基因表达和关键酶的翻译后修饰。在这里，我们报告水稻（Oryza sativa）叶绿体中镁（Mg）的diel波动，其可能充当节律调节剂，有助于水稻中光合作用CO ₂同化的翻译后调节。我们发现叶绿体定位的Mg ²⁺转运蛋白基因OsMGT3在叶肉细胞中有节奏地表达，其部分调节水稻叶绿体中的镁波动。敲除OsMGT3大大减少了Mg ^2+的吸收，以及叶绿体中Mg ²⁺的自由波动幅度，这与体内核糖1,5-二磷酸羧化酶活性的降低密切相关，从而导致光合速率下降。此外，OsMGT3的叶肉特异性过表达显着提高了水稻的光合作用效率和生长性能。综上所述，这些观察结果表明，在整个周期中，OsMGT3依赖的diel叶绿体中的Mg波动可能有助于Mg依赖的酶的光合作用。增强镁叶绿体的²⁺输入可能是提高植物光合作用效率的潜在方法。