A microRNA528-ZmLac3 module regulates low phosphate tolerance in maize.

MicroRNAs are known to play a crucial role in plant development and physiology and become a target for investigating the regulatory mechanism underlying plant low phosphate tolerance. ZmmiR528 has been shown to display significantly different expression levels between wild-type and low Pi-tolerant maize mutants. However, its functional role in maize low Pi tolerance remains unknown. In the present study, we studied the role and underlying molecular mechanism of miR528 in maize with low Pi tolerance. Overexpression of ZmmiR528 in maize resulted in impaired root growth, reduced Pi uptake capacity and compromised resistance to Pi deficiency. By contrast, transgenic maize plants suppressing ZmmiR528 expression showed enhanced low Pi tolerance. Furthermore, ZmLac3 and ZmLac5 which encode laccase were identified and verified as targets of ZmmiR528. ZmLac3 transgenic plants were subsequently generated and were also found to play key roles in regulating maize root growth, Pi uptake and low Pi tolerance. Furthermore, auxin transport was found to be potentially involved in ZmLac3-mediated root growth. Moreover, we conducted genetic complementary analysis through the hybridization of ZmmiR528 and ZmLac3 transgenic plants and found a favorable combination with breeding potential, namely anti-miR528:ZmLac3OE hybrid maize, which exhibited significantly increased low Pi tolerance and markedly alleviated yield loss caused by low Pi stress. Our study has thus identified a ZmmiR528-ZmLac3 module regulating auxin transport and hence root growth, thereby determining Pi uptake and ultimately low Pi tolerance, providing an effective approach for low Pi tolerance improvement through manipulating the expression of miRNA and its target in maize.

Transcriptomic and metabolomic profiling reveals the protective role of anthocyanins in alleviating low phosphate stress in maize.

Anthocyanin accumulation is a characteristic response to phosphate (Pi) deficiency in plants. In the present study, we investigated the role of maize anthocyanins (MA) in alleviating low Pi (LP) stress in maize (Zea mays L). To this end, maize plants were exposed to LP conditions and treated with or without (control) MA. Interestingly, MA-treated maize plants showed relieved growth inhibition, reproductive development retardation, and yield loss compared to control plants under LP stress. Moreover, the level of oxidative destruction was significantly alleviated in MA-treated plants compared to the untreated control under conditions of LP stress. Acid phosphatase (APase) activity was significantly higher in MA-treated plants than in control plants, resulting in enhanced Pi mobilization and recycling. The results of the transcriptome analysis suggested that genes involved in photosynthesis, photosystem light harvesting, Pi transport, and recycling were differentially expressed between MA-treated plants and control plants. Moreover, metabolome analysis indicated higher sugar and organic acid levels and lower phosphorylated metabolite contents in MA-treated plants than in control plants, which was consistent with the results of the comparative transcriptome analysis. Taken together, our findings indicate that MA plays critical roles in alleviating LP stress in maize plants, probably by improving photosynthetic performance and increasing Pi mobilization and recycling. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-00981-9.

Molecular characterization, expression and functional analysis of acyl-CoA-binding protein gene family in maize (Zea mays).

BACKGROUND: Acyl-CoA-binding proteins (ACBPs) possess a conserved acyl-CoA-binding (ACB) domain that facilitates binding to acyl-CoA esters and trafficking in eukaryotic cells. Although the various functions of ACBP have been characterized in several plant species, their structure, molecular evolution, expression profile, and function have not been fully elucidated in Zea mays L. RESULTS: Genome-wide analysis identified nine ZmACBP genes in Z. mays, which could be divided into four distinct classes (class I, class II, class III, and class IV) via construction of a phylogenetic tree that included 48 ACBP genes from six different plant species. Transient expression of a ZmACBP-GFP fusion protein in tobacco (Nicotiana tabacum) epidermal cells revealed that ZmACBPs localized to multiple different locations. Analyses of expression profiles revealed that ZmACBPs exhibited temporal and spatial expression changes during abiotic and biotic stresses. Eight of the nine ZmACBP genes were also found to have significant association with agronomic traits in a panel of 500 maize inbred lines. The heterologous constitutive expression of ZmACBP1 and ZmACBP3 in Arabidopsis enhanced the resistance of these plants to salinity and drought stress, possibly through alterations in the level of lipid metabolic and stress-responsive genes. CONCLUSION: The ACBP gene family was highly conserved across different plant species. ZmACBP genes had clear tissue and organ expression specificity and were responsive to both biotic and abiotic stresses, suggesting their roles in plant growth and stress resistance.

Genome-wide trait-trait dynamics correlation study dissects the gene regulation pattern in maize kernels.

BACKGROUND: Dissecting the genetic basis and regulatory mechanisms for the biosynthesis and accumulation of nutrients in maize could lead to the improved nutritional quality of this crop. Gene expression is regulated at the genomic, transcriptional, and post-transcriptional levels, all of which can produce diversity among traits. However, the expression of most genes connected with a particular trait usually does not have a direct association with the variation of that trait. In addition, expression profiles of genes involved in a single pathway may vary as the intrinsic cellular state changes. To work around these issues, we utilized a statistical method, liquid association (LA) to investigate the complex pattern of gene regulation in maize kernels. RESULTS: We applied LA to the expression profiles of 28,769 genes to dissect dynamic trait-trait correlation patterns in maize kernels. Among the 1000 LA pairs (LAPs) with the largest LA scores, 686 LAPs were identified conditional correlation. We also identified 830 and 215 LA-scouting leaders based on the positive and negative LA scores, which were significantly enriched for some biological processes and molecular functions. Our analysis of the dynamic co-expression patterns in the carotene biosynthetic pathway clearly indicated the important role of lcyE, CYP97A, ZEP1, and VDE in this pathway, which may change the direction of carotene biosynthesis by controlling the influx and efflux of the substrate. The dynamic trait-trait correlation patterns between gene expression and oil concentration in the fatty acid metabolic pathway and its complex regulatory network were also assessed. 23 of 26 oil-associated genes were correlated with oil concentration conditioning on 580 LA-scoutinggenes, and 5% of these LA-scouting genes were annotated as enzymes in the oil metabolic pathway. CONCLUSIONS: By focusing on the carotenoid and oil biosynthetic pathways in maize, we showed that a genome-wide LA analysis provides a novel and effective way to detect transcriptional regulatory relationships. This method will help us understand the biological role of maize kernel genes and will benefit maize breeding programs.

Overexpression of the protein phosphatase 2A regulatory subunit a gene ZmPP2AA1 improves low phosphate tolerance by remodeling the root system architecture of maize.

Phosphate (Pi) limitation is a constraint for plant growth and development in many natural and agricultural ecosystems. In this study, a gene encoding Zea mays L. protein phosphatase 2A regulatory subunit A, designated ZmPP2AA1, was induced in roots by low Pi availability. The function of the ZmPP2AA1 gene in maize was analyzed using overexpression and RNA interference. ZmPP2AA1 modulated root gravitropism, negatively regulated primary root (PR) growth, and stimulated the development of lateral roots (LRs). A detailed characterization of the root system architecture (RSA) in response to different Pi concentrations with or without indole-3-acetic acid and 1-N-naphthylphthalamic acid revealed that auxin was involved in the RSA response to low Pi availability. Overexpression of ZmPP2AA1 enhanced tolerance to Pi starvation in transgenic maize in hydroponic and soil pot experiments. An increased dry weight (DW), root-to-shoot ratio, and total P content and concentration, along with a delayed and reduced accumulation of anthocyanin in overexpressing transgenic maize plants coincided with their highly branched root system and increased Pi uptake capability under low Pi conditions. Inflorescence development of the ZmPP2AA1 overexpressing line was less affected by low Pi stress, resulting in higher grain yield per plant under Pi deprivation. These data reveal the biological function of ZmPP2AA1, provide insights into a linkage between auxin and low Pi responses, and drive new strategies for the efficient utilization of Pi by maize.

Identification and comparative analysis of low phosphate tolerance-associated microRNAs in two maize genotypes.

Low phosphate (Pi) availability is a major constraint on maize growth and productivity. MicroRNAs (miRNAs) are known to play critical roles in plant responses to various environmental conditions. The identification of low Pi tolerance-associated miRNAs will accelerate the development of Pi starvation tolerant maize plants. However, miRNAs associated with low Pi tolerance have not been identified. In this study, we compared deep sequencing small RNA reads from two maize genotypes, the wild type, Qi319, and the low Pi tolerant mutant, 99038, under normal and low Pi conditions. Six known miRNA families and seven novel miRNAs were found differently expressed by the two genotypes. All these miRNAs were confirmed by sequencing a second batch of small RNA libraries constructed in the same way as those used in the first sequencing. The expression profiles of some of these miRNAs were further confirmed by real-time PCR. The predicted target genes of the low Pi tolerance-associated miRNAs were involved in root development or stress responses. Expression levels of some of target genes were significantly different between Qi319 and 99038. These findings suggested that miRNAs may play important roles in low Pi tolerance in maize and may be a key factor in determining the level of low Pi tolerance in different maize genotypes. This study provides an approach for identifying low Pi tolerance-associated miRNAs and can help in the selection and manipulation of high performing maize genotypes under low Pi conditions.

Overexpression of Thellungiella halophila H+-pyrophosphatase gene improves low phosphate tolerance in maize.

Low phosphate availability is a major constraint on plant growth and agricultural productivity. Engineering a crop with enhanced low phosphate tolerance by transgenic technique could be one way of alleviating agricultural losses due to phosphate deficiency. In this study, we reported that transgenic maize plants that overexpressed the Thellungiella halophila vacuolar H(+)-pyrophosphatase gene (TsVP) were more tolerant to phosphate deficit stress than the wild type. Under phosphate sufficient conditions, transgenic plants showed more vigorous root growth than the wild type. When phosphate deficit stress was imposed, they also developed more robust root systems than the wild type, this advantage facilitated phosphate uptake, which meant that transgenic plants accumulated more phosphorus. So the growth and development in the transgenic maize plants were not damaged as much as in the wild type plants under phosphate limitation. Overexpression of TsVP increased the expression of genes involved in auxin transport, which indicated that the development of larger root systems in transgenic plants might be due in part to enhanced auxin transport which controls developmental events in plants. Moreover, transgenic plants showed less reproductive development retardation and a higher grain yield per plant than the wild type plants when grown in a low phosphate soil. The phenotypes of transgenic maize plants suggested that the overexpression of TsVP led to larger root systems that allowed transgenic maize plants to take up more phosphate, which led to less injury and better performance than the wild type under phosphate deficiency conditions. This study describes a feasible strategy for improving low phosphate tolerance in maize and reducing agricultural losses caused by phosphate deficit stress.