The ZmNF-YC1-ZmAPRG pathway modulates low phosphorus tolerance in maize.

Phosphorus (P) is an essential nutrient for plant growth and yield. Low phosphate use efficiency makes it important to clarify the molecular mechanism of low P stress. In our previous studies, a P efficiency gene ZmAPRG was identified. Here, we further screened the upstream regulator ZmNF-YC1 of ZmAPRG by yeast one hybrid (Y1H) assay, and found it was a low inorganic phosphorus (Pi)-inducible gene. The results of dual luciferase assays, expression analysis, and ChIP-qPCR assays showed that ZmNF-YC1 is a positive regulator of ZmAPRG. Overexpression of ZmNF-YC1 improved low P tolerance, whereas knockout of ZmNF-YC1 decreased low P tolerance in maize. Bimolecular fluorescence complementation (BiFC), yeast two hybrid (Y2H) assay, and yeast three hybrid (Y3H) assay further showed that ZmNF-YC1 can interact with ZmNF-YB14, and recruit ZmNF-YA4/10 to form NF-Y complexes. Transcriptional activation assay confirmed that the NF-Y complexes can activate the promoters of ZmAPRG. Meanwhile, transcriptome and metabolome analyses indicated that overexpression of ZmAPRG improves low P tolerance by regulating lipid composition and photosynthetic capacity, and chlorophyll fluorescence parameters provided evidence in support of this hypothesis. Furthermore, overexpression of ZmAPRG increased grain yield in inbred and hybrid maize under low P conditions. Taken together, our research revealed a low P tolerance mechanism of the ZmNF-YC1-ZmAPRG pathway.

Salt Tolerant Gene 1 contributes to salt tolerance by maintaining photosystem II activity in maize.

Salt stress is a major environmental factor limiting crop growth and productivity. Here, we show that Salt-Tolerant Gene 1 (ZmSTG1) contributes to salt tolerance by maintaining photosystem activity in maize. ZmSTG1 encodes an endoplasmic reticulum localized protein and retrotransposon insertion in the promoter region causes differential expression levels in maize inbred lines. Overexpression of ZmSTG1 improved plant growth vigor, and knockout of ZmSTG1 weakened plant growth under normal and salt stress conditions. Transcriptome and metabolome analyses indicated that ZmSTG1 might regulate the expression of lipid trafficking-related genes dependent on the abscisic acid (ABA) signaling pathway, thereby increasing the galactolipids and phospholipid concentrations in the photosynthetic membrane under salt stress. Chlorophyll fluorescence parameters showed that the knockout of ZmSTG1 led to significant impairment of plant photosystem II (PSII) activity under normal and salt stress conditions, whereas overexpression of ZmSTG1 dramatically improved plant PSII activity under salt stress conditions. We also demonstrated that the application of the salt-tolerant locus could enhance salt tolerance in hybrid maize plants. Taken together, we propose that ZmSTG1 may modulate the lipid composition in the photosynthetic membrane by affecting the expression of lipid trafficking-related genes to maintain the photosynthetic activity of plants under salt stress.

A new network containing MYB109-ZmCesA5 is involved in kernel development.

MYB genes regulate several different aspects of metabolism and development. However, few studies have reported the involvement of MYBs-CesAs network in the regulation of maize kernel development. In this study, yeast one-hybrid (Y1H) assays and dual-luciferase reporter assays showed that ZmMYB109 activated the expression of ZmCesA5 by directly binding to its promoter. Real-time quantitative PCR (RT-qPCR) and transcriptome analyses showed that ZmMYB109 expression increased in ZmCesA5-OE kernels and decreased in ZmCesA5-KO kernels. Overexpression of ZmCesA5 produced heavier kernels, whereas loss of function of ZmCesA5 affected starch and sucrose metabolism, resulting in weight reduction of the maize kernels. Collectively, these findings suggest that a new network containing MYB109-ZmCesA5 is involved in kernel development.

Maize transcription factor ZmNF-YC13 regulates plant architecture.

Leaf angle and leaf orientation value (LOV) are critical agronomic traits for maize plant architecture. The functions of NUCLEAR FACTOR Y (NF-Y) members in regulating plant architecture have not been reported yet. Here, we identified a regulator of maize plant architecture, NF-Y subunit C13 (ZmNF-YC13). ZmNF-YC13 was highly expressed in the leaf base zone of maize plants. ZmNF-YC13 overexpressing plants showed upright leaves with narrow leaf angle and larger LOV, while ZmNF-YC13 knockout plants had larger leaf angle and smaller LOV compared with wild-type plants. The changes in plant architecture were due to the changes in the expression of cytochrome P450 family members. ZmNF-YC13 interacts with two NF-Y subunit B members (ZmNF-YB9 and ZmNF-YB10) of the LEAFY COTYLEDON1 sub-family, and further recruits NF-Y subunit A (ZmNF-YA3) to form two NF-Y complexes. The two complexes can both activate the promoters of transcriptional repressors (ZmWRKY76 and ZmBT2), and the promoters of PLASTOCHRON group genes can be repressed by ZmWRKY76 and ZmBT2 in maize protoplasts. We propose that ZmNF-YC13 functions as a transcriptional regulator and, together with ZmNF-YBs and ZmNF-YA3, affects plant architecture by regulating the expression of ZmWRKY76 and ZmBT2, which repress the expression of cytochrome P450 family members in PLASTOCHRON branch.

Identification and characterization of paternal-preferentially expressed gene NF-YC8 in maize endosperm.

Gene imprinting describes an epigenetic phenomenon, whereby genetically identical alleles are differentially expressed dependent on parent-of-origin. Some imprinted genes belonged to NUCLEAR FACTOR Y (NF-Y) transcription factors, which were involved in many important metabolic processes in plant. The characterizations of imprinted genes are of great importance for their function exploration. In this paper, 15 non-redundant NF-YC genes were identified in the maize genome and the paternally expressed gene NF-YC8 was further analyzed. NF-YC8 primarily expressed in maize immature ear and tassel and phylogenetic analysis showed that NF-YC8 was highly homologous with Arabidopsis thaliana NF-YC2 genes which function in regulation of the flowering processes, ER stress response. Furthermore, NF-YC8 was a differential, gene-specific imprinted gene at 14 DAP and persistently imprinted throughout later endosperm development in the B73/Mo17 genetic background. Bisulfite sequencing for NF-YC8 in maize endosperm showed that the paternal alleles were higher methylated (CG, CHG and CHH contexts) than maternal alleles in the 5' upstream region, and the coding region was highly methylated in CG context. Additionally, TE (CG, CHG and CHH contexts) and repetitive region (CG and CHG contexts) were all highly methylated. These results are the first description of evolution and molecular characterization of maize NF-YC8 and will provide new references for maize NF-YC genetic analysis.

Overexpression of the maize transcription factor ZmVQ52 accelerates leaf senescence in Arabidopsis.

Leaf senescence plays an important role in the improvement of maize kernel yields. However, the underlying regulatory mechanisms of leaf senescence in maize are largely unknown. We isolated ZmVQ52 and studied the function of ZmVQ52 which encoded, a VQ family transcription factor. ZmVQ52 is constitutively expressed in maize tissues, and mainly expressed in the leaf; it is located in the nucleus of maize protoplasts. Four WRKY family proteins-ZmWRKY20, ZmWRKY36, ZmWRKY50, and ZmWRKY71-were identified as interacting with ZmVQ52. The overexpression of ZmVQ52 in Arabidopsis accelerated premature leaf senescence. The leaf of the ZmVQ52-overexpression line showed a lower chlorophyll content and higher senescence rate than the WT. A number of leaf senescence regulating genes were up-regulated in the ZmVQ52-overexpression line. Additionally, hormone treatments revealed that the leaf of the ZmVQ52-overexpressed line was more sensitive to salicylic acid (SA) and jasmonic acid (JA), and had an enhanced tolerance to abscisic acid (ABA). Moreover, a transcriptome analysis of the ZmVQ52-overexpression line revealed that ZmVQ52 is mainly involved in the circadian pathway and photosynthetic pathways.