Cadmium (Cd) is a nonessential heavy metal toxic to all organisms. Daily consumption of Cd contaminated rice has caused Itai-Itai disease in Japan. Cd in rice was found as high as 1–2 mg kg⁻¹ in some areas in China and is much higher than the national standard 0.2 mg kg⁻¹ (GB2762-2005), imposing great threat to both food security and safety. Therefore, reducing Cd accumulation in rice grains is highly demanded.

Previous QTL analysis identified OsHMA3 and CAL1 as two important players in Cd translocation between roots and shoots. OsHMA3 regulates cadmium translocation via the modulation of vacuolar sequestration capacity for Cd in rice roots. CAL1 encodes a defensin-like protein, which facilitates Cd loading into xylem vessels by chelation and the subsequent secretion from cytosol to apoplastic compartments. Here we reported the mapping and isolation of another major QTL SQ9, using the previously reported parental varieties CJ06 and TN01 as the derived mapping population. SQ9 is located on Chromosome 2 and contributes about 20% of the overall variance in Cd accumulation in rice grains. Pilot experiments showed that overexpression of the SQ9^TN1 increased Cd concentration in grains with CJ06 background, while reduced Cd concentrations in grains was observed in the knock-out mutants of SQ9 in TN1 background. We will further report and discuss the underlying mechanisms.