The OsSAPK2-OsNAC4 module couples water stress signaling with cadmium accumulation in rice.

Abstract

Water-saving cultivation practices, such as intermittent irrigation, are essential for sustainable rice production but often exacerbate grain cadmium (Cd) accumulation due to aerobic-soil-induced increases in Cd bioavailability. Uncoupling this trade-off is a critical challenge for global food safety. Here, we identify the transcription factor OsNAC4 as a key positive regulator of Cd uptake. Loss-of-function osnac4 mutants significantly reduce grain Cd accumulation by 30%-50% across diverse genetic backgrounds without compromising grain yield or agronomic traits. Mechanistically, we reveal that the drought/abscisic acid (ABA)-activated kinase OsSAPK2 interacts with and phosphorylates OsNAC4, thereby stabilizing the protein and enhancing its transcriptional activation of the Cd transporter gene OsNRAMP1. This signaling cascade establishes a direct molecular link whereby environmental water stress signaling cascades effectively "hijack" the basal Cd uptake machinery. Crucially, multi-location field trials demonstrate that osnac4 mutation effectively suppresses the aerobic-induced Cd elevation typically observed under water-saving regimes. Our findings elucidate the molecular mechanism underlying the conflict between water conservation and Cd accumulation, providing a robust genetic resource for breeding safe, climate-resilient rice varieties suitable for water-limited agriculture.