Comparison on cellular mechanisms of iron and cadmium accumulation in rice: prospects for cultivating Fe-rich but Cd-free rice

Rice, Aug 2016

Iron (Fe) is essential for rice growth and humans consuming as their staple food but is often deficient because of insoluble Fe(III) in soil for rice growth and limited assimilation for human bodies, while cadmium (Cd) is non-essential and toxic for rice growth and humans if accumulating at high levels. Over-accumulated Cd can cause damage to human bodies. Selecting and breeding Fe-rich but Cd-free rice cultivars are ambitious, challenging and meaningful tasks for researchers. Although evidences show that the mechanisms of Fe/Cd uptake and accumulation in rice are common to some extent as a result of similar entry routes within rice, an increasing number of researchers have discovered distinct mechanisms between Fe/Cd uptake and accumulation in rice. This comprehensive review systematically elaborates and compares cellular mechanisms of Fe/Cd uptake and accumulation in rice, respectively. Mechanisms for maintaining Fe homeostasis and Cd detoxicification are also elucidated. Then, effects of different fertilizer management on Fe/Cd accumulation in rice are discussed. Finally, this review enumerates various approaches for reducing grain Cd accumulation and enhancing Fe content in rice. In summary, understanding of discrepant cellular mechanisms of Fe/Cd accumulation in rice provides guidance for cultivating Fe-fortified rice and has paved the way to develop rice that are tolerant to Cd stress, aiming at breeding Fe-rich but Cd-free rice.

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Comparison on cellular mechanisms of iron and cadmium accumulation in rice: prospects for cultivating Fe-rich but Cd-free rice

Gao et al. Rice Comparison on cellular mechanisms of iron and cadmium accumulation in rice: prospects for cultivating Fe-rich but Cd-free rice Lei Gao 0 1 3 4 Jiadong Chang 0 1 3 4 Ruijie Chen 0 1 3 4 Hubo Li 0 1 3 4 Hongfei Lu 0 1 3 4 Longxing Tao 2 Jie Xiong 0 1 3 4 0 Zhejinag Province Key Laboratory of Plant Secondary Metabolism and Regulation , Hangzhou 310018 , People's Republic of China 1 College of Life Sciences, Zhejiang Sci-Tech University , Hangzhou 310018 , People's Republic of China 2 State Key Laboratory of Rice Biology, China National Rice Research Institute , Hangzhou 310006 , People's Republic of China 3 Zhejinag Province Key Laboratory of Plant Secondary Metabolism and Regulation , Hangzhou 310018 , People's Republic of China 4 College of Life Sciences, Zhejiang Sci-Tech University , Hangzhou 310018 , People's Republic of China Iron (Fe) is essential for rice growth and humans consuming as their staple food but is often deficient because of insoluble Fe(III) in soil for rice growth and limited assimilation for human bodies, while cadmium (Cd) is nonessential and toxic for rice growth and humans if accumulating at high levels. Over-accumulated Cd can cause damage to human bodies. Selecting and breeding Fe-rich but Cd-free rice cultivars are ambitious, challenging and meaningful tasks for researchers. Although evidences show that the mechanisms of Fe/Cd uptake and accumulation in rice are common to some extent as a result of similar entry routes within rice, an increasing number of researchers have discovered distinct mechanisms between Fe/Cd uptake and accumulation in rice. This comprehensive review systematically elaborates and compares cellular mechanisms of Fe/Cd uptake and accumulation in rice, respectively. Mechanisms for maintaining Fe homeostasis and Cd detoxicification are also elucidated. Then, effects of different fertilizer management on Fe/Cd accumulation in rice are discussed. Finally, this review enumerates various approaches for reducing grain Cd accumulation and enhancing Fe content in rice. In summary, understanding of discrepant cellular mechanisms of Fe/Cd accumulation in rice provides guidance for cultivating Fe-fortified rice and has paved the way to develop rice that are tolerant to Cd stress, aiming at breeding Fe-rich but Cd-free rice. Iron; Cadmium; Biofortification; Mugineic acid; Phytosiderophores; Phytochelatins; Harvestplus; Fertilizer management Review Metal elements, such as Fe, Zn, Mn and Cu, are essential for living organisms and present as ions. Although there are abundant metal elements in the earth’s crust, these ions, particularly Fe, are sparingly soluble under aerobic conditions in high pH or calcareous soils and are not bioavailable to plants (Takahashi et al. 2003) . As a result, Fe deficiency is a widespread agricultural problem that causes plants growth retardation and restricts sources of nutrition from plants (e.g., rice, maize and barley) (Mori 1999; Kobayashi et al. 2010) . In response to Fe deficiency, higher plants have developed two strategies for acquiring Fe from the rhizosphere (Conte and Walker, 2011; Kobayashi and Nishizawa, 2012) . The application of strategy I is non-graminaceous plants, which includes the reduction of Fe(III) to soluble Fe(II) by activating membrane-bound Fe(III)-chelate reductases, followed by uptake of the reduced Fe(II) into cytoplasm via Fe(II) transporters (Cheng et al. 2007) . Strategy II is employed only by graminaceous plants, such as rice. Roots can secrete phytosiderophores (PSs) that belongs to the muginneic acid (MA) family to rhizosphere and chelate Fe(III), followed by uptake of Fe(III)-PS complexes via specific plasma membrane transporters (Conte and Walker, 2011) . Rice utilizes strategy II to acquire Fe from rhizosphere and also possesses strategy I-like system that can take in Fe(II) directly (Cheng et al. 2007) . In spite of rice can apply specific strategies to acquire Fe, these mechanisms have limited accessibility to resource-poor people faced with Fe deficiency from certain areas of the world. To deal with limited Fe and improve human Fe nutritional status, biofortifying rice with enhanced Fe absorption will be an effective method for populations consuming rice as their staple food. Cd is a toxic heavy metal and accumulation of Cd in rice grains poses a latent health problem to human. Cd in human body can lead to chronic toxicity. The outbreak of “Itai-Itai disease” in the mid-20th century in Japan is due to consumption of Cd-contaminated rice (Uraguchi et al. 2011) . A person with “Itai-Itai” has symptoms of weakness and softening of the bones (Horiguchi et al. 2010). Cd enters into environment, such as soil and river mainly through industrial activities or fertilizers (Bolan et al. 2003) . As a mobile and soluble metal, Cd causes crops yield reduction and does harm to human health even at low concentrations (Choppala et al. 2014) . The primary effects on plants caused (...truncated)


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Lei Gao, Jiadong Chang, Ruijie Chen, Hubo Li, Hongfei Lu, Longxing Tao, Jie Xiong. Comparison on cellular mechanisms of iron and cadmium accumulation in rice: prospects for cultivating Fe-rich but Cd-free rice, Rice, 2016, pp. 39, Volume 9, Issue 1, DOI: 10.1186/s12284-016-0112-7