Biofortification of iron content by regulating a NAC transcription factor in maize.

Iron (Fe) deficiency remains widespread among people in developing countries. To help solve this problem, breeders have been attempting to develop maize cultivars with high yields and high Fe concentrations in the kernels. We conducted a genome-wide association study and identified a gene, ZmNAC78 (NAM/ATAF/CUC DOMAIN TRANSCRIPTION FACTOR 78), that regulates Fe concentrations in maize kernels. We cultivated maize varieties with both high yield and high Fe concentrations in their kernels by using a molecular marker developed from a 42-base pair insertion or deletion (indel) in the promoter of ZmNAC78. ZmNAC78 expression is enriched in the basal endosperm transfer layer of kernels, and the ZmNAC78 protein directly regulates messenger RNA abundance of Fe transporters. Our results thus provide an approach to develop maize varieties with Fe-enriched kernels.

Maize Dek407 Encodes the Nitrate Transporter 1.5 and Is Required for Kernel Development.

The kernel serves as the storage organ and harvestable component of maize, and it plays a crucial role in determining crop yield and quality. Understanding the molecular and genetic mechanisms of kernel development is of considerable importance for maize production. In this study, we obtained a mutant, which we designated defective kernel 407 (dek407), through ethyl methanesulfonate mutagenesis. The dek407 mutant exhibited reduced kernel size and kernel weight, as well as delayed grain filling compared with those of the wild type. Positional cloning and an allelism test revealed that Dek407 encodes a nitrate transporter 1/peptide transporter family (NPF) protein and is the allele of miniature 2 (mn2) that was responsible for a poorly filled defective kernel phenotype. A transcriptome analysis of the developing kernels showed that the mutation of Dek407 altered the expression of phytohormone-related genes, especially those genes associated with indole-3-acetic acid synthesis and signaling. Phytohormone measurements and analysis indicated that the endogenous indole-3-acetic acid content was significantly reduced by 66% in the dek407 kernels, which may be the primary cause of the defective phenotype. We further demonstrated that natural variation in Dek407 is associated with kernel weight and kernel size. Therefore, Dek407 is a potential target gene for improvement of maize yield.

The auxin signaling pathway contributes to phosphorus-mediated zinc homeostasis in maize.

Although the interaction between P and Zn has long been recognized in plants, the physiological and molecular mechanisms underlying P and Zn interactions are poorly understood. We show here that P supply decreases the Zn concentration in maize shoots and roots. Compared to +P + Zn (addition of both P and Zn), +P-Zn reduced and -P-Zn increased the total length of 1° lateral roots (LRs). Under +P + Zn, both P and Zn concentrations were lower in the sl1 mutant roots than in wild-type (WT) maize roots, and P accumulation did not reduce the Zn concentration in ll1 mutant roots. Transcriptome profiling showed that the auxin signaling pathway contributed to P-mediated Zn homeostasis in maize. Auxin production and distribution were altered by changes in P and Zn supply. Cytosolic Zn co-localized with auxin accumulation under +P + Zn. Exogenous application of 1-NAA and L-Kyn altered the P-mediated root system architecture (RSA) under Zn deficiency. -P-Zn repressed the expression of miR167. Overexpression of ZmMIR167b increased the lengths of 1° LRs and the concentrations of P and Zn in maize. These results indicate that auxin-dependent RSA is important for P-mediated Zn homeostasis in maize.HighlightAuxin-dependent RSA is important for P-mediated Zn homeostasis in maize.

Integrating BSA-Seq with RNA-Seq Reveals a Novel Fasciated Ear5 Mutant in Maize.

Increasing grain yield is required to meet the rapidly expanding demands for food, feed, and fuel. Inflorescence meristems are central to plant growth and development. However, the question concerning whether inflorescence development can be regulated to improve grain yield remains unclear. Here, we describe a naturally occurring single recessive mutation called fea5 that can increase grain yield in maize. Using bulk segregant analysis sequencing (BSA-seq), the candidate region was initially mapped to a large region on chromosome 4 (4.68 Mb-11.26 Mb). Transcriptome sequencing (RNA-seq) revealed a total of 1246 differentially expressed genes (DEGs), of which 835 were up-regulated and 411 were down-regulated. Further analysis revealed the enrichment of DEGs in phytohormone signal transduction. Consistently, phytohormone profiling indicated that auxin (IAA), jasmonic acid (JA), ethylene (ETH), and cytokinin (CK) levels increased significantly, whereas the gibberellin (GA) level decreased significantly in fea5. By integrating BSA-seq with RNA-seq, we identified Zm00001d048841 as the most likely candidate gene. Our results provide valuable insight into this new germplasm resource and the molecular mechanism underlying fasciated ears that produce a higher kernel row number in maize.

Pre-rRNA processing and its response to temperature stress in maize.

Ribosome biogenesis is a fundamental process in all eukaryotic cells and is coupled with the processing and maturation of pre-rRNAs. Maize is a primary staple crop across the world, but little is known about the exact pre-rRNA processing sites and pathways in this species. In this study, we present a detailed model of the pathway by identifying the critical endonucleolytic cleavage sites and determining the pre-rRNA intermediates by circular reverse-transcription PCR and northern blot analysis. We demonstrate that two pathways coexist in maize to promote the processing of 35S pre-rRNA, and that the processing of 27SA pre-rRNA can proceed via two different pathways, which are distinguished based on the order of ITS1 removal and ITS2 cleavage. Compared with yeast and mammals, this new 27SA pre-rRNA processing mechanism is unique to maize and other higher plants. In addition, we demonstrate that maize can modulate pre-rRNA processing levels in response to chilling and heat stress, as indicated by a significant reduction of the P-A3 intermediate. Our study provides information that will facilitate future research on ribosome biogenesis and pre-rRNA processing in maize.

Genetic-based dissection of arsenic accumulation in maize using a genome-wide association analysis method.

Understanding the mechanism of arsenic (As) accumulation in plants is important in reducing As's toxicity to plants and its potential risks to human health. Here, we performed a genome-wide association study to dissect the genetic basis of the As contents of different maize tissues in Xixian, which was irrigated with As-rich surface water, and Changge using an association population consisting of 230 representative maize inbred lines. Phenotypic data revealed a wide normal distribution and high repeatability for the As contents in maize tissues. The As concentrations in maize tissues followed the same trend in the two locations: kernels < axes < stems < bracts < leaves. In total, 15, 16 and 15 non-redundant quantitative trait loci (QTLs) associated with As concentrations were identified (P ≤ 2.04 × 10-6 ) in five tissues from Xixian, Changge, and the combination of the locations, respectively, explaining 9.70%-24.65% of the phenotypic variation for each QTL, on average. Additionally, four QTLs [involving 15 single nucleotide polymorphisms (SNPs)] were detected in the single and the combined locations, indicating that these loci/SNPs might be stable across different environments. The candidate genes associated with these four loci were predicted. In addition, four non-redundant QTLs (6 SNPs), including a QTL that was detected in multiple locations according to the genome-wide association study, were found to co-localize with four previously reported QTL intervals. These results are valuable to understand the genetic architecture of As mechanism in maize and facilitate the genetic improvement of varieties without As toxicity.