A rice ABC transporter, OsABCC1, reduces arsenic accumulation in the grain

Arsenic (As) is a chronic poison that causes severe skin lesions and cancer. Rice (Oryza sativa L.) is a major dietary source of As; therefore, reducing As accumulation in the rice grain and thereby diminishing the amount of As that enters the food chain is of critical importance. Here, we report that a member of the Oryza sativa C-type ATP-binding cassette (ABC) transporter (OsABCC) family, OsABCC1, is involved in the detoxification and reduction of As in rice grains. We found that OsABCC1 was expressed in many organs, including the roots, leaves, nodes, peduncle, and rachis. Expression was not affected when plants were exposed to low levels of As but was up-regulated in response to high levels of As. In both the basal nodes and upper nodes, which are connected to the panicle, OsABCC1 was localized to the phloem region of vascular bundles. Furthermore, OsABCC1 was localized to the tonoplast and conferred phytochelatin-dependent As resistance in yeast. Knockout of OsABCC1 in rice resulted in decreased tolerance to As, but did not affect cadmium toxicity. At the reproductive growth stage, the As content was higher in the nodes and in other tissues of wild-type rice than in those of OsABCC1 knockout mutants, but was significantly lower in the grain. Taken together, our results indicate that OsABCC1 limits As transport to the grains by sequestering As in the vacuoles of the phloem companion cells of the nodes in rice.open117318Ysciescopu

OsHKT1;5 mediates Na(+) exclusion in the vasculature to protect leaf blades and reproductive tissues from salt toxicity in rice

Salt tolerance QTL analysis of rice has revealed that the SKC1 locus, which is involved in a higher K(+) /Na(+) ratio in shoots, corresponds to the OsHKT1;5 gene encoding a Na(+) -selective transporter. However, physiological roles of OsHKT1;5 in rice exposed to salt stress remain elusive and no OsHKT1;5 gene disruption mutants have been characterized to date. In this study, we dissected two independent T-DNA insertional OsHKT1;5 mutants. Measurements of ion contents in tissues and (22) Na(+) tracer imaging experiments showed that loss-of-function of OsHKT1;5 in salt-stressed rice roots triggers massive Na(+) accumulation in shoots. Salt stress-induced increases in the OsHKT1;5 transcript was observed in roots and basal stems including basal nodes. Immuno-staining using an anti-OsHKT1;5 peptide antibody indicated that OsHKT1;5 is localized in cells adjacent to the xylem in roots. Additionally, direct introduction of (22) Na(+) tracer to leaf sheaths also demonstrated the involvement of OsHKT1;5 in xylem Na(+) unloading in leaf sheaths. Furthermore, OsHKT1;5 was indicated to present in the plasma membrane and found to localize also in the phloem of diffuse vascular bundles in basal nodes. Together with the characteristic (22) Na(+) allocation in the blade of the developing immature leaf in the mutants, these results suggest a novel function of OsHKT1;5 in mediating Na(+) exclusion in the phloem to prevent Na(+) transfer to young leaf blades. Our findings further demonstrate that the function of OsHKT1;5 is crucial over growth stages of rice, including the protection of the next generation seeds as well as of vital leaf blades under salt stress. This article is protected by copyright. All rights reserved