Genome-wide association mapping identifies a new arsenate reductase enzyme critical for limiting arsenic accumulation in plants.

Dai-Yin Chao,Jiugeng Chen,David E Salt,John M Danku,Chengcheng Wang,Yi Chen,Fang-Jie Zhao,Shulin Shi,Ziru Chen,Julin N Maloof

doi:10.1371/journal.pbio.1002009

Abstract

Author SummaryArsenic is a human carcinogen that accumulates from soil into many different food crops, where it presents a significantly increased cancer risk when foods derived from these crops are consumed. Plants naturally control the amount of arsenic they accumulate by first chemically converting arsenate into arsenite, which is then extruded from the roots back into the soil. Because arsenate is a chemical analogue of phosphate, conversion of arsenate in the root to arsenite may also prevent arsenic being efficiently transported to the shoots via the phosphate transport system. The chemical reduction of arsenate to generate arsenite is therefore clearly a key component of a plant's detoxification strategy. Here, we use genetic methods to identify the enzyme responsible for this crucial reaction—HAC1. We show that HAC1 is responsible for arsenate reductase activity in both the outer layer of the root (epidermis) and the inner layer adjacent to the xylem (pericycle). In its absence, the roots return less arsenic to the soil and the shoots accumulate up to 300 times more arsenic. This knowledge creates new opportunities to limit arsenic accumulation in food crops, thereby helping to reduce the cancer risk from this food-chain contaminant.

Highlights

Inorganic arsenic is a non-threshold class-1 chronic exposure human carcinogen [1], and its elevated level in rice (Oryza sativa) produced in Bangladesh, China, and India is known to pose a significantly elevated cancer risk in these populations, which eat rice at the high levels typical of many Southeast Asian countries [2,3]
Arsenic is a human carcinogen that accumulates from soil into many different food crops, where it presents a significantly increased cancer risk when foods derived from these crops are consumed
We show that High Arsenic Content 1 (HAC1) is responsible for arsenate reductase activity in both the outer layer of the root and the inner layer adjacent to the xylem

Summary

Introduction

Inorganic arsenic is a non-threshold class-1 chronic exposure human carcinogen [1], and its elevated level in rice (Oryza sativa) produced in Bangladesh, China, and India is known to pose a significantly elevated cancer risk in these populations, which eat rice at the high levels typical of many Southeast Asian countries [2,3]. Several brands of baby food and juice contain arsenic concentrations that exceed the United States federal arsenic limit for drinking water [4,5] raising significant health concerns in the US and Europe [6,7,8]. Because of this serious and widespread food safety concern research into understanding the mechanisms driving arsenic accumulation in plants has become a priority [9]. The function of this ACR2-like gene in arsenic metabolism in A. thaliana appears unlikely

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