Researchers find that duplicating a transporter gene reduces toxic cadmium buildup in rice without affecting quality and yield


Rice is a staple food for almost half of the world’s population. However, it accumulates more cadmium from the soil than other grains like barley and wheat. Reports estimate that 40-65% of our total consumption of cadmium, a toxic heavy metal, comes from rice. Consumption of cadmium-contaminated rice poses a serious risk to human health, with conditions such as Itai-itai disease being associated with a high intake of cadmium.

Efforts have already been made to reduce the amount of cadmium in rice through methods such as importing clean soil, water management, and mixing contaminated soil with biochar and lime. However, these methods are time consuming and expensive. To address this, scientists have turned to crossbreeding to grow rice that accumulates less cadmium.

“We have been working on the mechanisms of cadmium accumulation in rice and barley for a long time and have identified several key genes involved in its accumulation”, explains Professor Jian Feng Ma, affiliated with the Institute of Plant Sciences and Resources of University of Okayama, Japan. Recently, Professor Ma published an article in the journal natural food detailing the genetic mechanisms that play a role in this process. The article was published online on August 18, 2022 (August 19, 2022, Japan time).

After examining 132 rice accessions, Professor Ma and members of his research group found that the OsNramp5 gene, when duplicated in tandem, reduced cadmium accumulation in Pokkali, a rice variety that has been cultivated for 3000 years in Kerala, India. According to previous reports, OsNramp5 encodes a cadmium and manganese transporter protein in rice. The same gene, when duplicated in tandem, increases uptake of both minerals in root cells. Therefore, manganese competes with cadmium in cells for translocation to shoots, which in turn reduces cadmium accumulation in these parts.

Scientists found that out of the 132 rice accessions, the tandem duplication of OsNramp5 was naturally found only in Pokkali, which can grow in salt-laden coastal soil.

The researchers also noted that the level of spatial expression of OsNramp5 was always about twice as high in Pokkali roots as in Koshihikari roots.

Because Pokkali stores extremely little cadmium in its shoots, scientists introgressed (a term for the transfer of genetic information between species) the duplicated OsNramp5 gene in Koshihikari, a rice variety that is very popular in Japan but accumulates relatively high levels. high in cadmium. Explaining how targeted breeding can help humans, Professor Ma says: “We identified a gene responsible for differential cadmium accumulation in rice grain based on natural variations in cadmium accumulation. Then we applied this gene to successfully breed rice cultivars with low cadmium accumulation in cereals.”

The team found that the Koshihikari cultivar with the duplicated gene accumulated significantly lower amounts of cadmium without compromising grain quality or yield.

Recounting the benefits of a variety of rice with low cadmium accumulation, Professor Ma explains: “Cadmium is a toxic heavy metal and threatens our health all along the food chain. Our study has provided useful material for the selection of rice varieties with low cadmium accumulation, which contributes to producing safe and healthy foods. We hope that this gene will be widely used in the breeding of different rice cultivars with low cadmium accumulation. This will protect us from cadmium poisoning.

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Materials provided by Okayama University. Note: Content may be edited for style and length.


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