Gene limiting cadmium accumulation in rice.

Area of Science:

• Plant Molecular Biology
• Agricultural Science
• Environmental Toxicology

Background:

• Cadmium (Cd) accumulation in rice poses a significant food safety risk, linked to Itai-itai disease.
• The molecular mechanisms governing Cd accumulation in rice remain largely unknown.
• Controlling soil Cd uptake is crucial for preventing human health issues.

Purpose of the Study:

• To identify the gene responsible for low cadmium accumulation in rice.
• To elucidate the molecular mechanism of cadmium control in rice.
• To investigate potential strategies for reducing cadmium in edible rice parts.

Main Methods:

• Gene isolation using a mapping population from high and low Cd-accumulating rice cultivars.
• Heterologous expression in yeast to assess transporter function.
• Analysis of gene expression in root cells.
• Overexpression studies in rice to evaluate cadmium reduction.

Main Results:

• A gene, OsHMA3, encoding a P1B-type ATPase transporter, was identified as responsible for low Cd accumulation.
• A single amino acid mutation in OsHMA3 from high-Cd cultivars likely inactivates the transporter.
• OsHMA3 functions by sequestering cadmium into root vacuoles, limiting its translocation to above-ground tissues.
• Overexpression of functional OsHMA3 significantly reduced grain cadmium without affecting other micronutrients.

Conclusions:

• OsHMA3 is a key determinant of low cadmium accumulation in rice.
• This transporter selectively sequesters cadmium in root vacuoles, preventing its entry into the food chain.
• OsHMA3 offers a promising target for developing low-cadmium rice varieties to improve food safety.