Low cadmium (LCD), a novel gene related to cadmium tolerance and accumulation in rice seeds

Cadmium (Cd) contamination of food crops is a major concern in food production, leading to reduced crop yields and threatening human health. In 2004, the Joint FAO/WHO Expert Committee on Food Additives, in association with the Codex Alimentarius Commission, established allowable limits for Cd levels in food; for rice, the limit is 0.4 mg/kg of Cd. The basic mechanisms that control the accumulation of Cd in the edible parts of plants are poorly understood, and without adequate knowledge concerning these regulatory processes, progress toward limiting the accumulation of Cd in food crops will be slow. In the present study, we screened knockout rice (Oryza sativa) plants, tagged with the gene trap vector pGA2707, for Cd tolerance and obtained the tolerant line lcd. The lcd line showed tolerance to Cd at early stages of plant development during the screening process in Murashige and Skoog medium and in hydroponic culture. Metal concentration measurements from hydroponic culture revealed that a significantly lower amount of Cd accumulated in lcd shoots than in wild-type (WT) shoots. When cultured in soil containing a low level of Cd, lcd showed no significant difference in Cd content in leaf blades, but the Cd content in seeds was 16% lower, complying with the Cd limit established by the Codex Alimentarius. There were no significant differences in plant dry weight or seed yield between lcd and WT plants. These data indicate that lcd is a promising candidate rice line for use in combating the threat of Cd to human health