Ion-beam irradiation, gene identification, and marker-assisted breeding in the development of low-cadmium rice

Abstract

Rice (Oryza sativa L.) grain is a major dietary source of cadmium (Cd), which is toxic to humans, but no practical technique exists to substantially reduce Cd contamination. Carbon ion-beam irradiation produced three rice mutants with <0.05 mg Cd·kg −1 in the grain compared with a mean of 1.73 mg Cd·kg −1 in the parent, Koshihikari. We identified the gene responsible for reduced Cd uptake and developed a strategy for marker-assisted selection of low-Cd cultivars. Sequence analysis revealed that these mutants have different mutations of the same gene (OsNRAMP5), which encodes a natural resistance-associated macrophage protein. Functional analysis revealed that the defective transporter protein encoded by the mutant osnramp5 greatly decreases Cd uptake by roots, resulting in decreased Cd in the straw and grain. In addition, we developed DNA markers to facilitate marker-assisted selection of cultivars carrying osnramp5. When grown in Cd-contaminated paddy fields, the mutants have nearly undetectable Cd in their grains and exhibit no agriculturally or economically adverse traits. Because mutants produced by ionbeam radiation are not transgenic plants, they are likely to be accepted by consumers and thus represent a practical choice for rice production worldwide.

Zinc-Finger Transcription Factor ZAT6 Positively Regulates Cadmium Tolerance through the Glutathione-Dependent Pathway in Arabidopsis

“…In addition, a lot of key genes have been shown to be involved in Cd detoxification and tolerance in plants. These include ZNT1, OsHMA9, OsNRAMP5, ZntA, CAD2, AtPDR12, AtPDR8, AtATM3, ACBP1, Nramp5, EIN2, and MAN3 (Pence et al, 2000;Sharma et al, 2000;Shiraishi et al, 2000;Lee et al, 2003Lee et al, , 2007Kim et al, 2006Kim et al, , 2007Xiao et al, 2008;Cao et al, 2009;Lin and Aarts, 2012;Sasaki et al, 2012;Ishikawa et al, 2012;Chen et al, 2015). It was also found that Heat shock transcription factor A4a (HsfA4a) confers Cd tolerance by up-regulating MT gene expression in wheat (Triticum aestivum) and rice (Oryza sativa; Shim et al, 2009).…”

Effect of high-LET Fe-ion beam irradiation on mutation induction in <i>Arabidopsis thaliana</i>

“…Heavy-ion irradiation has also been accepted as a powerful mutagen for both forward and reverse genetics. Therefore, studies on biological processes in plants and microbes have been advanced by using heavy-ion irradiation (Hase et al, 2000(Hase et al, , 2006Shitsukawa et al, 2007;Shimada et al, 2009;Yasui et al, 2011;Fujita et al, 2012;Sasaki et al, 2012;Ishikawa et al, 2012;Kazama et al, 2013;Hirano et al, 2013;Ma et al, 2013).…”

The HvNramp5 Transporter Mediates Uptake of Cadmium and Manganese, But Not Iron

“…5 and 6). In rice, Mn and Cd also share the same transporter, OsNramp5, for the uptake Ishikawa et al, 2012;Sasaki et al, 2012), although HvNramp5 differs from OsNramp5 in terms of expression patterns, tissue localization, and specificity of transport substrate as discussed below.…”

“…On the other hand, OsNrat1 (OsNramp4) transports trivalent Al ion (Xia et al, 2010) and is required for high Al tolerance in rice roots. Finally, OsNramp5 functions as a major transporter responsible for root Mn and Cd uptake Ishikawa et al, 2012;Sasaki et al, 2012). However, the function of OsNramp2, OsNramp6, and OsNramp7 is unknown.…”