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

The contamination of food crops by cadmium (Cd) is a major concern in food production because it can reduce crop yields and threaten human health. In this study, knockout rice plants (Oryza sativa) tagged with the gene trap vector pGA2707 were screened for Cd tolerance, and the tolerant line lcd was obtained. The lcd mutant showed tolerance to Cd on agar plates and in hydroponic culture during early plant development. Metal concentration measurements in hydroponically grown plants revealed significantly less Cd in the shoots of lcd plants compared with wild-type (WT) shoots. When cultured in the field in soil artificially contaminated with low levels of Cd, lcd showed no significant difference in the Cd content of its leaf blades; however, the Cd concentration in the grains was 55% lower in 2009 and 43% lower in 2010. There were no significant differences in plant dry weight or seed yield between lcd and wild-type plants. LCD, a novel gene, is not homologous to any other known gene. LCD localized to the cytoplasm and nucleus, and was expressed mainly in the vascular tissues in the roots and phloem companion cells in the leaves. These data indicate that lcd may be useful for understanding Cd transport mechanisms and is a promising candidate rice line for use in combating the threat of Cd to human health

The OsNRAMP1 iron transporter is involved in Cd accumulation in rice

Cadmium (Cd) is a heavy metal toxic to humans and the accumulation of Cd in the rice grain is a major agricultural problem, particularly in Asia. The role of the iron transporter OsNRAMP1 in Cd uptake and transport in rice was investigated here. An OsNRAMP1:GFP fusion protein was localized to the plasma membrane in onion epidermal cells. The growth of yeast expressing OsNRAMP1 was impaired in the presence of Cd compared with yeast transformed with an empty vector. Moreover, the Cd content of OsNRAMP1-expressing yeast exceeded that of the vector control. The expression of OsNRAMP1 in the roots was higher in a high Cd-accumulating cultivar (Habataki) than a low Cd-accumulating cultivar (Sasanishiki) regardless of the presence of Cd, and the amino acid sequence of OsNRAMP1 showed 100% identity between Sasanishiki and Habataki. Over-expression of OsNRAMP1 in rice increased Cd accumulation in the leaves. These results suggest that OsNRAMP1 participates in cellular Cd uptake and Cd transport within plants, and the higher expression of OsNRAMP1 in the roots could lead to an increase in Cd accumulation in the shoots. Our results indicated that OsNRAMP1 is an important protein in high-level Cd accumulation in rice

Crystal structure and regulation of the citrus pol III repressor MAF1 by auxin and phosphorylation

MAF1 is the main RNA polymerase (Pol) III repressor that controls cell growth in eukaryotes. The Citrus ortholog, CsMAF1, was shown to restrict cell growth in citrus canker disease but its role in plant development and disease is still unclear. We solved the crystal structure of the globular core of CsMAF1, which reveals additional structural elements compared with the previously available structure of hMAF1, and explored the dynamics of its flexible regions not present in the structure. CsMAF1 accumulated in the nucleolus upon leaf excision, and this translocation was inhibited by auxin and by mutation of the PKA phosphorylation site, S45, to aspartate. Additionally, mTOR phosphorylated recombinant CsMAF1 and the mTOR inhibitor AZD8055 blocked canker formation in normal but not CsMAF1-silenced plants. These results indicate that the role of TOR on cell growth induced by Xanthomonas citri depends on CsMAF1 and that auxin controls CsMAF1 interaction with Pol III in citrusThis work was supported by Sa˜ o Paulo Research Foundation (FAPESP grant 2011/20468-1). C.E.B. and A.F.Z.N. received a fellowship from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).Peer reviewe

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

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

Characterization of OsNramp1, a metal transporter from rice

Cadmium (Cd) is one of the most toxic heavy metals for both plants and humans, and Cd accumulation in rice grains has become a major agricultural problem in Japan. In this study, we investigated the role of OsNramp1 in Cd uptake and transport in rice. An OsNramp1::GFP fusion protein localized to the plasma membrane in onion epidermal cells, and yeast expressing OsNramp1 showed increased sensitivity to Cd. Furthermore, OsNramp1-overexpressing rice accumulated more Cd in the leaf blades than non-transformed rice when cultured in Cd-contaminated soil. These results suggest that OsNramp1 increases the cellular uptake and accumulation of Cd in plants

From laboratory to field: OsNRAMP5-knockdown rice is a promising candidate for Cd phytoremediation in paddy fields.

Previously, we reported that OsNRAMP5 functions as a manganese, iron, and cadmium (Cd) transporter. The shoot Cd content in OsNRAMP5 RNAi plants was higher than that in wild-type (WT) plants, whereas the total Cd content (roots plus shoots) was lower. For efficient Cd phytoremediation, we produced OsNRAMP5 RNAi plants using the natural high Cd-accumulating cultivar Anjana Dhan (A5i). Using a positron-emitting tracer imaging system, we assessed the time-course of Cd absorption and accumulation in A5i plants. Enhanced 107Cd translocation from the roots to the shoots was observed in A5i plants. To evaluate the phytoremediation capability of A5i plants, we performed a field experiment in a Cd-contaminated paddy field. The biomass of the A5i plants was unchanged by the suppression of OsNRAMP5 expression; the A5i plants accumulated twice as much Cd in their shoots as WT plants. Thus, A5i plants could be used for rapid Cd extraction and the efficient phytoremediation of Cd from paddy fields, leading to safer food production

Expression analysis of Anjana Dhan <i>OsNRAMP5</i> RNAi (A5i) plants.

<p>Expression of <i>OsIRT1</i> (A) and <i>OsNRAMP1</i> (B) in the roots of A5i plants in the absence of Cd. The results are presented as the means ± SD of three reactions. Different letters indicate significant differences at <i>P</i><0.05 according to Duncan’s test.</p