A new gene that significantly reduces cadmium levels in rice

Cadmium (Cd) is a heavy metal that can be hazardous to health when it accumulates in the human body through the food chain. Globally, cadmium contamination of soil is a serious health threat.

Nearly half of the world's population relies on rice as a staple diet, and it absorbs more cadmium from the soil than other grains like barley and wheat do. It is estimated that 40-65% of the total human intake of the toxic heavy metal cadmium comes from rice. Cadmium causes a large loss of calcium from human bones, leading to osteoporosis, bone atrophy, and joint pain. The "painful disease" that occurred in Japan in the early years is related to high cadmium intake.

Cadmium uptake by rice has previously been reduced by replacing clean soil, water management, and mixing contaminated soil with biochar and lime. However, these methods are time-consuming and expensive. Therefore, it is critical for human health to tap into superior genes that can reduce cadmium uptake in rice and breed rice varieties that can significantly reduce cadmium accumulation, thereby solving the problem of excessive cadmium levels in rice.

Recently, Professor Jianfeng Ma's team from Okayama University, Japan, published a research paper entitled "Duplication of a manganese/cadmium transporter gene reduces cadmium accumulation in rice" grain in Nature Food. The study successfully cloned a master QTL gene for cadmium uptake in rice, which significantly reduced the cadmium content in rice seeds and provided an effective and superior genetic resource for low cadmium breeding in rice.

Rice cadmium usually shares a transport protein with the essential divalent elements manganese, zinc or iron, so reducing cadmium levels through gene editing and other means often also reduces these essential plant elements, resulting in lower yields, etc. In this new study, the team identified a copy number doubling mutation in the manganese/cadmium transporter protein gene OsNramp5 in an old rice variety, Pokkali, as the main cause of low cadmium accumulation. Tandem duplication of this gene doubled the expression of the OsNramp5 gene, but its spatial expression pattern and cellular localization were not altered.

The elevated expression of OsNramp5 decreased Cd release to xylem while increasing Cd and Mn absorption by root cells. The good rice variety "Koshihikari" was backcrossed with this allele, which greatly decreased the buildup of Cd in rice cultivated in Cd-contaminated soils while having no influence on other crucial aspects of the plant, such as seed yield and flavor.

This study offers a useful target for rice breeding with low cadmium accumulation in addition to illuminating the molecular basis of low cadmium accumulation in rice.

In addition, antibodies can be developed against cadmium as a semi-antigen to further develop corresponding diagnostics and therapeutics.

Heavy metals cannot directly elicit immunological reactions, hence they are not immunogens to produce antibodies. However, heavy metals can be covalently combined with chelators to form metal-chelate complexes that can then be attached to immunogenic carrier proteins to elicit an immunological response. The metal-binding site of either native or metal-modified molecules may be recognized by the antibodies produced.

The design and synthesis of the heavy metals hapten are the essential steps to the detection of metal ions in environmental and dietary samples among all the immunoassay development processes for heavy metal ions. The simplicity of producing antibodies and the specificity of antibodies are determined by hapten design based on the appropriate bifunctional chelators employed to produce the immunogen. The main idea behind how heavy metals hapten is to use covalently loaded chelators to create metal-chelate complexes and metal-chelate-protein conjugates, which are then coupled to carrier proteins. The most often used chelators are EDTA and DTPA, cyclohexyl-DTPA, and phenanthroline derivatives. The carrier proteins include ovalbumin (OVA), bovine serum albumin (BSA), phenanthroline derivative, and hemocyanin (KLH) (HRP).

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