Natural variations in the P-type ATPase heavy metal transporter ZmHMA3 controlling cadmium accumulation in maize grains.

Cadmium (Cd) accumulation in maize grains is detrimental to human health. Developing maize varieties with low-Cd contents is important for maize grains safe consumption. However, the key genes controlling maize grain Cd accumulation have not been cloned. Here, we identified one major locus for maize grain Cd accumulation (qCd1) using a genome-wide association study (GWAS) and bulked segregant RNA-seq analysis with a biparental segregating population of Jing724 (low-Cd line) and Mo17 (high-Cd line). The candidate gene ZmHMA3 was identified by fine mapping, which encodes a tonoplast-localized heavy metal P-type ATPase transporter. An EMS mutant analysis and an allelism test confirmed that ZmHMA3 influences maize grain Cd accumulation. A transposon in intron 1 of ZmHMA3 is responsible for the abnormal amino acid sequence in Mo17. Based on the natural sequence variations in ZmHMA3 gene of diverse maize lines, four PCR-based molecular markers were developed, which were successfully used to distinguish five haplotypes with different grain Cd contents in the GWAS panel and to predict grain Cd content levels of widely used maize inbred lines and hybrids. These molecular markers can be used to breed elite maize varieties with low grain Cd contents.