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

Abstract

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.A rsenic (As) is a highly toxic metalloid that is classified as a nonthreshold class-1 carcinogen (1, 2). Long-term exposure to As in humans causes a number of diseases, including hyperpigmentation, keratosis, and skin and internal cancers (3). Due to As contamination of drinking water and soil from both anthropogenic and geogenic sources, millions of people worldwide suffer from As toxicity. This problem is particularly serious in countries in South and Southeast Asia, such as India and Bangladesh, where groundwater, which is used both as a drinking water supply and for irrigating rice, contains high concentrations of As (4). Therefore, reducing the As concentration in drinking water and foods is a critical goal for promoting human health.Rice (Oryza sativa L.), a staple food of half of the world's human population, is a major dietary source of As (5, 6). A recent cohort study in West Bengal, India showed that high concentrations of As in rice are associated with elevated genotoxic effects in humans (7). Rice accumulates As in the shoots and grains more efficiently than do other cereal crops such as wheat (Triticum aestivum) and barley (Hordeum vulgare) (8, 9). This higher efficiency has been attributed to the increased bioavailability of As under flooded conditions (such as those found in paddy fields) and the efficient As uptake system in rice (10-12). In the anaerobic paddy field, As is mainly present in the form of arsenite, which is taken up by two silicon (Si) transporters-namely, Lsi1 (low silicon 1), a Si influx transporter, and Lsi2 (low silicon 2), a Si efflux transporter (11). These transpo...

Orchestration of three transporters and distinct vascular structures in node for intervascular transfer of silicon in rice

“…Recently, identification of mineral nutrient transporters in node and physiological studies shed a new light on the importance of node for preferential distribution of mineral nutrients to developing and reproductive organs (2,14,(18)(19)(20)(21)(22)(23). The xylem flow in EVBs and DVBs, which are connected by nodal vascular anastomosis (NVA) at the base of the node, are simply divided following the transpiration rate of each upper organ.…”

Arsenic Accumulation in Rice and Probable Mitigation Approaches: A Review

“…Besides arsenate reduction, phytochelatin-arsenite complexation and subsequent sequestration into the vacuoles constitute another important pathway of arsenic detoxification in plants [58]. Being the precursor compound of phytochelatin (PC) synthesis, glutathione (GSH) plays a crucial role in arsenic tolerance.…”

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A natural rice rhizospheric bacterium abates arsenic accumulation in rice (Oryza sativa L.)

“…In contrast to Lsi2, Lsi1 is a bidirectional channel, and a portion of As(III) taken up by Lsi1 is released back into the rhizosphere (Zhao et al 2010a), while the remaining As(III) is sequestered into root vacuoles or translocated into different plant organs (Zhao et al 2010b). Recently, a rice ABC transporter (OsABCC1) was identified that limits the As transport to the grains by sequestering As into the vacuoles of the phloem companion cells of the nodes in the rice (Song et al 2014). In the paddy soil solution, the coexistence of As(III) and As(V) with more ratio of As (III) has been shown (Panaullah et al 2009).…”