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

Cadmium (Cd) accumulation in maize grains is detrimental to human health. Developing maize varieties with low Cd content is important for safe consumption of maize grains. 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 and encodes a tonoplast-localized heavy metal P-type ATPase transporter. An ethyl methane sulfonate 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 the ZmHMA3 gene of diverse maize lines, four PCR-based molecular markers were developed, and these were successfully used to distinguish five haplotypes with different grain Cd contents in the GWAS panel and to predict grain Cd contents of widely used maize inbred lines and hybrids. These molecular markers can be used to breed elite maize varieties with low grain Cd contents.

Genome-wide identification, characterization, and expression analysis of the monovalent cation-proton antiporter superfamily in maize, and functional analysis of its role in salt tolerance.

Na+, K+ and pH homeostasis are important for plant life and they are controlled by the monovalent cation proton antiporter (CPA) superfamily. The roles of ZmCPAs in salt tolerance are not fully elucidated. In this study, we identified 35 ZmCPAs comprising 13 Na+/H+ exchangers (ZmNHXs), 16 cation/H+ exchanger (ZmCHXs), and 6 K+ efflux antiporters (ZmKEAs). All ZmCPAs have transmembrane domains and most of them were localized to plasma membrane or tonoplast. ZmCHXs were specifically highly expressed in anthers, while ZmNHXs and ZmKEAs showed high expression in various tissues. ZmNHX5 and ZmKEA2 were up-regulated in maize seedlings under both NaCl and KCl stresses. Yeast complementation experiments revealed the roles of ZmNHX5, ZmKEA2 in NaCl tolerance. Analysis of the maize mutants further validated the salt tolerance functions of ZmNHX5 and ZmKEA2. Our study highlights comprehensive information of ZmCPAs and provides new gene targets for salt tolerance maize breeding.

Sequence polymorphism of the waxy gene in waxy maize accessions and characterization of a new waxy allele.

Waxy maize has many excellent characteristics in terms of its nutritional and economic value. In recent decades, the waxy maize germplasm has increased dramatically as a result of different selection methods. We collected 200 waxy maize inbred accessions from different origins to study their genetic diversity and phylogenetic relationships, and to identify new waxy mutations. A simple sequence repeat (SSR) analysis revealed wide genetic diversity among the 200 waxy maize accessions. The maize accessions were clustered into three groups. We sequenced the waxy gene from the first to the 14th exon. Nucleotide variation analysis of 167 waxy maize and 14 flint maize lines revealed some nucleotide differences in the waxy gene among different waxy maize groups, and much narrower nucleotide diversity in waxy maize than in flint maize. In a phylogenetic analysis, waxy maize carrying the same mutation allele clustered together, and waxy maize carrying different mutation alleles distributed in different groups; waxy maize was intermixed with flint maize in each branch, and wx-D7 waxy maize separated significantly from waxy maize lines carrying wx-D10, wx-124 and wx-hAT mutant alleles. The wx-hAT was a new waxy mutation identified in this study. It consisted of a 2286-bp transposon inserted into the middle of exon three of the waxy gene. A PCR marker specific for the wx-hAT allele was developed. These results will be useful for the utilization and preservation of the waxy maize germplasm, and the PCR marker has potential uses in waxy maize breeding programs.

Transcriptome analysis of a novel maize bsd C4 mutant using RNA-seq.

The C4 plants like maize are at an advantage because they exhibit higher carbon conversion efficiency than C3 during photosynthesis. Using the evaluation of photosynthetic phenotypes and subcellular structure, and high-quality transcriptome analysis for four types of leaves from a bundle sheath defective maize mutant (bsd) and 501 wild line, the key target genes, important transcription factors, and specific pathways were obtained, which may regulate the C-concentrating mechanisms and antioxidant protection of the photosynthetic system, gibberellin signaling, ribosome editing, glycolysis, and chlorophyll biosynthesis. Based on these target genes, a novel network with photosynthetic transformation efficiency with oxidative decarboxylation and ribosome regulation was filtered innovatively by Cytoscape, which adds to our understanding for high-efficiency C-fixation and its genetic improvement in C3 and C4 plants.