Scientists uncover molecular mechanism linking water-saving irrigation to cadmium accumulation in rice
Chinese Academy of Sciences Headquarters
image:
A proposed working model illustrating how ABA signaling links water status to Cd accumulation via theOsSAPK2-OsNAC4-OsNRAMP1 module in rice
view moreCredit: SHEN Renfang's team
Water-saving irrigation practices, including intermittent irrigation, are essential for sustainable rice cultivation amid growing freshwater shortages. However, periodic drainage creates aerobic soil conditions that drastically boost cadmium (Cd) bioavailability, leading to severe grain Cd enrichment. Disentangling the relationship between water conservation and high grain Cd has been a critical challenge for rice breeders and soil scientists worldwide.
Now, a research team led by Profs. SHEN Renfang and ZHU Xiaofang from the Institute of Soil Science of the Chinese Academy of Sciences has identified a conserved molecular cascade that explains this phenomenon. Published online in Current Biology on July 8, the study demonstrates that drought and abscisic acid (ABA) signaling actively trigger excessive Cd uptake in rice under water-saving regimes.
Using CRISPR-Cas9 mutant screening, biochemical assays, and multi-location field trials, the researchers identified the transcription factor OsNAC4 as a key regulator of grain Cd accumulation. Phenotypic assays across multiple genetic backgrounds validated that the functional knockout of OsNAC4 reduces grain Cd concentrations by 30%–50% under intermittent irrigation, without any negative impacts on grain yield or key agronomic traits.
The researchers also identified the OsSAPK2–OsNAC4–OsNRAMP1 regulatory pathway as the mechanism by which OsNAC4 controls grain Cd accumulation. Under aerobic or drought conditions, activated endogenous ABA signaling stimulates the SnRK2-type kinase OsSAPK2, which then physically interacts with and phosphorylates OsNAC4 at four conserved serine residues. This process stabilizes OsNAC4 and enhances its DNA-binding affinity, thereby upregulating expression of OsNRAMP1. The OsNRAMP1 protein is a major plasma membrane transporter mediating root Cd uptake. This pathway is the molecular basis of the elevated levels of grain Cd that appear when rice plants face drought stress as part of water-saving irrigation practices.
Importantly, rice plants lacking OsNAC4 preserve the basal transport of essential metals like manganese and iron required for normal development even as stress-triggered excess Cd uptake is suppressed. In contrast, rice plants carrying direct mutations in genes encoding OsNRAMP family transporters often exhibit disrupted nutrient homeostasis and severe growth defects.
"Our work demonstrates that elevated grain Cd under drainage is not merely a passive consequence of soil redox shifts; rather, plants actively amplify Cd absorption via endogenous ABA signaling cascades in response to aerobic environments," said Prof. ZHU, one of the lead authors.
By characterizing the OsSAPK2–OsNAC4–OsNRAMP1 pathway, this study provides a precise theoretical framework to decouple water stress signaling from heavy metal accumulation, offering an effective breeding target to develop climate-resilient, low-Cd rice varieties compatible with water-limited agriculture.
Journal
Current Biology
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
The OsSAPK2–OsNAC4 Module Couples Water Stress Signaling with Cadmium Accumulation in Rice
Article Publication Date
8-Jul-2026
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