Water-saving irrigation methods such as intermittent flooding help conserve freshwater in rice farming but create aerobic soil conditions that increase cadmium bioavailability and raise grain cadmium content. Researchers from the Institute of Soil Science at the Chinese Academy of Sciences have now identified a molecular cascade that explains this link. Their findings, published in Current Biology, show that drought and abscisic acid signaling promote excessive cadmium uptake through the OsSAPK2-OsNAC4-OsNRAMP1 pathway. Using CRISPR-Cas9 screening, biochemical tests and field trials, the team found that OsNAC4 regulates cadmium accumulation. Knocking out this transcription factor lowered grain cadmium by 30 to 50 percent under intermittent irrigation without harming yield or other traits. Under aerobic conditions, ABA signaling activates OsSAPK2, which phosphorylates and stabilizes OsNAC4, boosting expression of the cadmium transporter OsNRAMP1. Plants without OsNAC4 maintain normal uptake of essential metals such as manganese and iron. The study indicates that elevated cadmium is not solely due to soil chemistry changes but results from active plant responses to water stress, offering a potential target for breeding low-cadmium rice suited to water-limited conditions.
