Gene edit boosts rice safety while preserving high harvest yields

Cadmium (Cd) contamination is a growing threat to food safety, and rice is one of the most vulnerable crops. Because rice plants can accumulate cadmium from contaminated soils more readily than many other staples, Cd can become a major dietary exposure route for large parts of the world’s population. Yet attempts to lower cadmium often create trade-offs—reducing uptake of essential nutrients or weakening plant performance.

A new study from Okayama University, Japan, and collaborating researchers in China reports a precision-editing strategy designed to avoid those trade-offs. The team focused on the rice metal transporter gene OsNramp5, which is known to move metals such as manganese and cadmium, and used base-editing to search for a beneficial point mutation within the gene rather than disabling it.

Using adenine and cytosine base editors, the researchers generated more than 1,600 genome-edited rice lines and screened them for reduced cadmium accumulation. Their saturation mutagenesis approach targeted OsNramp5 to identify variants that kept normal plant physiology while limiting Cd buildup in grain.

The key breakthrough was the I441T substitution: changing isoleucine to threonine at amino acid position 441. This single change reduced cadmium levels in both shoots and brown rice without altering gene expression, protein abundance, or the subcellular localization of the transporter.

Importantly, the mutation did not come at the cost of micronutrients. Field trials on cadmium-contaminated soil showed a 48% decrease in cadmium concentration in brown rice, from 0.14 mg/kg in wild type to 0.07 mg/kg in the edited plants, while iron, manganese, and zinc levels remained essentially unchanged.

The researchers then explored the mechanism behind the selective effect. Although OsNramp5 transports multiple metals, the I441T mutation shifted its selectivity—enhancing zinc transport preference. Increased zinc accumulation in root cells promoted competitive inhibition against cadmium during root-to-shoot movement.

Instead of completely blocking cadmium uptake, the edited transporter selectively limited cadmium translocation, reducing grain contamination while preserving essential mineral delivery. The team supported these conclusions with physiological assessments, gene and protein analyses, yeast transport assays, and agronomic evaluation.

Overall, the work demonstrates how precision genome editing can address a long-standing breeding challenge: lowering toxic metal accumulation without disrupting nutrient homeostasis. The researchers propose that the OsNramp5^I441T allele could accelerate development of safer rice varieties for mildly contaminated regions.