The endoplasmic reticulum-localized Ca²⁺-ATPase OsACA5 regulates immunity and the seed setting rate in rice

Calcium signaling plays a central role in plant immunity and development, and its homeostasis relies on the precise regulation of calcium transporters such as Ca²⁺-ATPases. However, the mechanisms by which Ca²⁺-ATPases coordinate disease resistance and reproductive development in rice remain largely unclear. In this study, we investigated the function of the endoplasmic reticulum (ER)-localized Ca²⁺-ATPase gene Oryza sativa autoinhibited Ca²⁺-ATPase 5 (OsACA5). The expression of OsACA5 was induced by infection with the rice blast fungus Magnaporthe oryzae and by the pathogen-associated molecular pattern (PAMP) flg22. In contrast, loss-of-function osaca5 mutants exhibited significantly enhanced resistance to rice blast, as evidenced by reduced lesion areas, increased reactive oxygen species (ROS) production, and elevated expression of defense-related genes, indicating that OsACA5 acts as a negative regulator of plant immunity. Further analyses revealed that OsACA5 negatively regulates early PAMP-triggered immunity (PTI)-associated Ca²⁺ influx induced by flg22 and chitin, thereby suppressing immune activation. In addition to enhanced disease resistance, osaca5 mutants displayed notable agronomic changes, including reduced seed setting rate and plant height, as well as increased thousand-grain weight and grain length. Together, these findings demonstrate that OsACA5 plays a critical role in balancing disease resistance and reproductive development in rice by modulating PTI-associated calcium signaling, providing new insights into the regulatory function of ER-localized Ca²⁺-ATPases and offering a potential strategy for breeding rice varieties with stable disease resistance and optimized yield-related traits.