Low-light stress compromises photosynthetic and energy efficiency and leads to spikelet sterility; however, the effect of low-light stress on pollen tube elongation in the pistil remains poorly understood. The gene RGA1, which encodes a Gα-subunit of the heterotrimeric G-protein, enhanced low-light tolerance at anthesis by preventing the cessation of pollen tube elongation in the pistil of rice plants. In this process, marked increases in the activities of acid invertase (INV), sucrose synthase (SUS) and mitochondrial respiratory electron transport chain complexes, as well as the relative expression levels of SUTs (sucrose transporter), SWEETs (sugars will eventually be exported transporters), SUSs, INVs, CINs (cell-wall INV 1), SnRK1A (sucrose-nonfermenting 1-related kinase 1) and SnRK1B, were observed in OE-1 plants. Accordingly, notable increases in contents of ATP and ATPase were presented in OE-1 plants under low-light conditions, while they were decreased in d1 plants. Importantly, INV and ATPase activators (sucrose and Na 2 SO 3 , respectively) increased spikelet fertility by improving the energy status in the pistil under low-light conditions, and the ATPase inhibitor Na 2 VO 4 induced spikelet sterility and decreased ATPase activity. These results suggest that RGA1 could alleviate the low-light stress-induced impairment of pollen tube elongation to increase spikelet fertility by promoting sucrose unloading in the pistil and improving the metabolism and allocation of energy. K E Y W O R D S energy metabolism and allocation, low-light stress, rice, sugar transport and metabolism 1 | INTRODUCTION Rice (Oryza sativa) is a critically important crop that feeds more than half of the world's population (Horie, 2019). However, increases in yield are impeded by adverse environmental factors, such as extreme temperatures, drought, salt stress and low-light stress, which might increase in severity with continued global warming driven by industrial development and anthropogenic activities (Horie, 2019; Long et al., 2022). China has faced various challenges associated with dimming, which is associated with alterations in the amount of solar radiation reaching the Earth's surface due to long-term continuous rain and increases in aerosol pollution, and these problems have only