The Maize Imprinted Gene Floury3 Encodes a PLATZ Protein Required for tRNA and 5S rRNA Transcription through Interaction with RNA Polymerase III

A candidate association study of transcription factors in maize revealed the ZmPLATZ15-ZmEREB200 module as a key regulator of waterlogging tolerance at the seedling stage

Soil waterlogging is a major abiotic stress that severely impairs maize growth and development by inducing hypoxic conditions that disrupt essential physiological processes. Transcription factors (TFs) play crucial roles in modulating plant responses to waterlogging stress by regulating the expression of stress-related genes that enhance or diminish stress tolerance. In this study, we conducted an association analysis to identify 11 TFs closely associated with waterlogging stress in maize. Notably, the PLATZ family emerged as a novel and significant contributor to waterlogging stress. Overexpression of ZmPLATZ15 resulted in increased sensitivity to waterlogging at maize seedlings. Conversely, ZmEREB200, a member of the maize Group VII ERF (ZmERFVII) family, was significantly downregulated in the ZmPLATZ15 overexpression lines under waterlogging stress. Promoter analysis revealed that ZmPLATZ15 regulates ZmEREB200 by binding to the A/T-rich motifs in the ZmEREB200 promoter. Interestingly, overexpression of ZmEREB200 was found to enhance waterlogging tolerance at maize seedlings. To further elucidate their roles, we analyzed the transcriptomic profiles of ZmPLATZ15 and ZmEREB200 overexpression lines under waterlogging stress. The overlapping differentially expressed genes in both ZmPLATZ15 and ZmEREB200 overexpression lines were significantly enriched in pathways associated with redox balance and salicylic acid metabolism, both of which are crucial for modulating waterlogging tolerance at maize seedlings. Metabolomic analysis revealed that antioxidant enzyme activity, salicylic acid, and glutathione levels were decreased in OE-ZmPLATZ15, while these metabolites were significantly increased in OE-ZmEREB200. These contrasting metabolic responses in overexpression lines may underlie their different tolerances to waterlogging stress. Our findings provide valuable insights into the regulatory mechanisms underlying maize's response to waterlogging stress and highlight the potential of TFs as tools for developing maize varieties with enhanced waterlogging tolerance.

Multi-Omics Analysis Reveals Differential Molecular Responses of RNA Polymerase Common Subunit ZmRPABC5b for Seedling Development in Maize

The normal development of maize (Zea mays) seedling is a prerequisite for achieving high crop yields. Although numerous molecular pathways regulate seedling development, the role of RNA polymerases (RNAPs) in this process remains largely unclear, and the function of common RNAP subunits in plants are not well understood. Here, we characterized the loss-of-function mutant of common subunit ZmRPABC5b, defective kernel 701 (dek701), which displays delayed seedling development. To elucidate the role of ZmRPABC5b in maize seedling growth, we conducted transcriptomic and metabolomic analyses. This study found that the loss of ZmRPABC5b function severely impaired early seedling growth, leading to significant reductions in stem length, root length, as well as fresh and dry weight. Transcriptome analysis identified 3780 upregulated and 4385 downregulated differentially expressed genes (DEGs) in dek701 seedlings compared to wild type. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of DEGs revealed that significant enrichment in pathways related to RNA biosynthesis, carbohydrate metabolic, hormone stimulus, cellular transporter and ribosome activity. Metabolome analysis identified 501 differentially expressed metabolites (DEMs) in dek701 seedlings, which were significantly enriched in the amino acid metabolism, secondary metabolites, carbohydrate metabolism, lipid metabolism, transport and translation. These findings provide substantial insight into the ZmRPABC5b regulatory network, positioning it as a central hub for regulating seedling development in maize.

PLATZ transcription factors and their emerging roles in plant responses to environmental stresses

Plant A/T-rich sequence- and zinc-binding (PLATZ) family proteins represent a novel class of plant-specific transcription factors that bind to A/T-rich sequences. Advances in high-throughput sequencing and bioinformatics analyses have facilitated the identification of numerous PLATZ proteins across various plant species. Over the last decade, accumulating evidence from omics analyses, genetics studies, and gain- and loss-of function investigations has indicated that PLATZ proteins play crucial roles in the complex regulatory networks governing plant development and adaptation to environmental stress. Recently, an excellent review has been published highlighting the roles of PLATZ proteins in controlling plant developmental processes. However, a comprehensive review specifically addressing the molecular mechanisms by which these proteins drive their functions in plant responses to environmental cues is currently lacking. In this review, we summarize the characteristics and identification of PLATZ proteins, emphasizing their significance in stress responses. We also highlight the crosstalk between PLATZ proteins and phytohormones. Furthermore, we discuss the downstream target genes, interacting partners, and upstream regulatory mechanisms associated with PLATZ proteins, providing a thorough understanding of their multifaceted roles in plants.

Natural variation of CT2 affects the embryo/kernel weight ratio in maize

Embryo size is a critical trait determining not only grain yield but also the nutrition of the maize kernel. Up to the present, only a few genes have been characterized affecting the maize embryo/kernel ratio. Here, we identify 63 genes significantly associated with maize embryo/kernel weight ratio using a genome-wide association study (GWAS). The peak GWAS signal shows that the natural variation in Zea mays COMPACT PLANT2 (CT2), encoding the heterotrimeric G protein α subunit, is significantly associated with the Embryo/Kernel Weight Ratio (EKWR). Further analyses show that a missense mutation of CT2 increases its enzyme activity and associates with EKWR. The function of CT2 on affecting embryo/kernel weight ratio is further validated by the characterization of two ct2 mutants, for which EKWR is significantly decreased. Subsequently, the key downstream genes of CT2 are identified by combining the differential expression analysis of the ct2 mutant and quantitative trait transcript analysis in the GWAS population. In addition, the allele frequency spectrum shows that CT2 was under selective pressure during maize domestication. This study provides important genetic insights into the natural variation of maize embryo/kernel weight ratio, which could be applied in future maize breeding programs to improve grain yield and nutritional content.

Exploring the Roles of the Plant AT-Rich Sequence and Zinc-Binding (PLATZ) Gene Family in Tomato (Solanum lycopersicum L.) Under Abiotic Stresses

PLATZ transcription factors represent a novel class of zinc finger proteins unique to plants and play critical roles in plant growth and stress responses. This study performs a bioinformatic analysis on the PLATZ transcription factor family in tomato. In the tomato genome, 20 PLATZ transcription factors were identified, distributed across nine chromosomes, including two tandem duplication clusters and two segmental duplication events. Phylogenetic analysis classified tomato PLATZ family members into five subgroups, with consistent gene structures and motif distributions within the same subfamily. The stress-responsive and hormone signaling elements were widely distributed in the promoters of SlPLATZs. The qRT-PCR results showed that most tested SlPLATZs were highly expressed in flowers and significantly expressed under different abiotic stresses (PEG, low temperature, and salt treatments) and hormone treatments (ABA and SA). In addition, we determined that SlPLATZ13/17/18/19 showed transcriptional inhibitory activities via yeast and dual-luciferase reporter assays. The interactions between SlPLATZ17, SlDREB2, and SlDREB31 were preliminarily confirmed via yeast two-hybrid assays. Overall, this study provides a valuable theoretical foundation for functional function research on PLATZ transcription factors, particularly in response to abiotic stresses.

Genetic dissection of internode length confers improvement for ideal plant architecture in maize

The optimal plant architecture, characterized by short stature, helps mitigate lodging, enables high-density planting, and facilitates mechanized harvesting. Internode length (IL), a crucial component of plant height in maize, plays a significant role in these processes. However, the genetic mechanisms underlying internode elongation remain poorly understood. In this study, we conducted a genome-wide association study to dissect the genetic architecture of IL in maize. The lengths of five internodes above and below the ear (referred as IL-related traits) were collected across multiple environments, revealing substantial variation. A total of 108 quantitative trait loci (QTL) were associated with 11 IL-related traits, with 17 QTL co-detected by different traits. Notably, three QTL have been selected in maize breeding progress. Three hundred and three genes associated with IL were found to operate through plant hormone signal transduction, receptor activity, and carbon metabolism pathways, influencing internode elongation. ZmIL1, which encodes alcohol dehydrogenase, exhibited a high expression level in internodes during the vegetative stage and has been selected in Chinese modern maize breeding. Additionally, ZmIL2 and ZmIL3 emerged as other crucial regulators of IL. Importantly, ZmIL1 has potential applications in maize varieties in the Huang-Huai-Hai region. This study represents the first comprehensive report on the genetic architecture of nearly all ILs in maize, providing profound insights into internode elongation mechanisms and genetic resources. These findings hold significant implications for dwarf breeding programs aimed at optimizing plant architecture for enhancing agronomic performance.

Genome-Wide Study of Plant-Specific PLATZ Transcription Factors and Functional Analysis of OsPLATZ1 in Regulating Caryopsis Development of Rice (Oryza sativa L.)

Plant A/T-rich sequence- and zinc-binding protein (PLATZ) is a type of plant-specific zinc-dependent DNA-binding protein that binds to A/T-rich DNA sequences. This family is essential for plant growth, development, and stress response. In this study, 15 OsPLATZs were identified in the rice genome with complete PLATZ-conserved domains by CD-search, similar to those found in angiosperms. Multi-species phylogenetic analysis showed that PLATZs were conserved in photosynthetic organisms, and an evolutionary branch unique to angiosperms was identified among members of the PLATZ family. Fifteen OsPLATZs were represented by five groups, each with distinct characteristics. An analysis of protein structures and sequence motifs showed that OsPLATZs were similar within groups, but varied between them. The expression profile and qRT-PCR results showed that OsPLATZs had distinct expression patterns in different tissues, with some responding to stress induction. Most of the OsPLATZs localized to the nuclei, and were predicted to bind to DNA sequences by AlphaFold3, suggesting that they likely function as conventional transcription factors. We also identified OsPLATZ1, a caryopsis-specific gene that regulates grain filling and caryopsis development in rice. This research lays the foundation for exploring the structural diversity, evolutionary traits, expression profile, and possible roles of PLATZ transcription factors in rice.

Comprehensive analysis of PLATZ family genes and their responses to abiotic stresses in Barley

BACKGROUND

Plant A/T-rich protein and zinc-binding protein (PLATZ) transcription factors are pivotal regulators in various aspects of plant biology, including growth, development, and responses to environmental stresses. While PLATZ genes have been extensively studied and functionally characterized in various plants, limited information is available for these genes in barley.

RESULTS

Here, we discovered a total of 11 PLATZ genes distributed across seven chromosomes in barley. Based on phylogenetic and conserved motif analysis, we classified PLATZ into five subfamilies, comprising 3, 1, 2, 1 and 4 genes, respectively. Analysis of gene structure demonstrated that these 11 HvPLATZ genes typically possessed two to four exons. Most HvPLATZ genes were found to possess at least one ABRE cis-element in their promoter regions, and a few of them also contained LTR, CAT-box, MRE, and DRE cis-elements. Then, we conducted an exploration of the expression patterns of HvPLATZs, which displayed notable differences across various tissues and in response to abiotic stresses. Functional analysis of HvPLATZ6 and HvPLATZ8 in yeast cells showed that they may be involved in drought tolerance. Additionally, we constructed a regulatory network including miRNA-targeted gene predictions and identified two miRNAs targeting two HvPLATZs, such as hvu-miR5053 and hvu-miR6184 targeting HvPLATZ2, hvu-miR6184 targeting HvPLATZ10.

CONCLUSION

In summary, these findings provide valuable insights for future functional verification of HvPLATZs and contribute to a deeper understanding of the role of HvPLATZs in response to stress conditions in barley.

The Role of PLATZ6 in Raffinose Family Oligosaccharides Loading of Leaves via PLATZ Family Characterization in Cucumber

The plant AT protein and zinc-binding protein (PLATZ) genes, a novel cluster of plant-specific zinc-finger-dependent DNA-binding proteins, play a crucial role in regulating stress response and plant development. However, there has been little study focus on the role of the cucumber PLATZ family in assimilating loading in leaves. (1) In this study, a total of 12 PLATZ genes were identified from the cucumber genome. The cucumber PLATZ genes were clustered into five groups, and unevenly distributed on five chromosomes. A single pair of cucumber PLATZ genes underwent segmental duplication. (2) The results of genome-wide expression analysis suggested that the cucumber PLATZ genes were widely expressed in a wide range of cucumber tissues, with three PLATZ (PLATZ2, PLATZ6, and PLATZ12) genes exhibiting high expression in the vascular tissues of cucumber leaves. PLATZ2, PLATZ6, and PLATZ12 proteins were primarily located in cytomembrane and nucleus. (3) In VIGS-PLATZ6 plants, the expression of Galactinol synthase 1 (GolS1) and STACHYOSE SYNTHASE (STS), two genes involved in the synthesis of raffinose family oligosaccharides (RFOs) were observed to be decreased in cucumber leaves. In conclusion, the comprehensive analysis of the cucumber PLATZ family and the preliminary functional verification of PLATZ6 lay the foundation for the molecular and physiological functions of cucumber PLATZ genes.

Identification and Functional Characterization of Abiotic Stress Tolerance-Related PLATZ Transcription Factor Family in Barley (Hordeum vulgare L.)

Plant AT-rich sequence and zinc-binding proteins (PLATZs) are a novel category of plant-specific transcription factors involved in growth, development, and abiotic stress responses. However, the PLATZ gene family has not been identified in barley. In this study, a total of 11 HvPLATZs were identified in barley, and they were unevenly distributed on five of the seven chromosomes. The phylogenetic tree, incorporating PLATZs from Arabidopsis, rice, maize, wheat, and barley, could be classified into six clusters, in which HvPLATZs are absent in Cluster VI. HvPLATZs exhibited conserved motif arrangements with a characteristic PLATZ domain. Two segmental duplication events were observed among HvPLATZs. All HvPLATZs were core genes present in 20 genotypes of the barley pan-genome. The HvPLATZ5 coding sequences were conserved among 20 barley genotypes, whereas HvPLATZ4/9/10 exhibited synonymous single nucleotide polymorphisms (SNPs); the remaining ones showed nonsynonymous variations. The expression of HvPLATZ2/3/8 was ubiquitous in various tissues, whereas HvPLATZ7 appeared transcriptionally silent; the remaining genes displayed tissue-specific expression. The expression of HvPLATZs was modulated by salt stress, potassium deficiency, and osmotic stress, with response patterns being time-, tissue-, and stress type-dependent. The heterologous expression of HvPLATZ3/5/6/8/9/10/11 in yeast enhanced tolerance to salt and osmotic stress, whereas the expression of HvPLATZ2 compromised tolerance. These results advance our comprehension and facilitate further functional characterization of HvPLATZs.

ZmPTOX1, a plastid terminal oxidase, contributes to redox homeostasis during seed development and germination

Maize plastid terminal oxidase1 (ZmPTOX1) plays a pivotal role in seed development by upholding redox balance within seed plastids. This study focuses on characterizing the white kernel mutant 3735 (wk3735) mutant, which yields pale-yellow seeds characterized by heightened protein but reduced carotenoid levels, along with delayed germination compared to wild-type (WT) seeds. We successfully cloned and identified the target gene ZmPTOX1, responsible for encoding maize PTOX-a versatile plastoquinol oxidase and redox sensor located in plastid membranes. While PTOX's established role involves regulating redox states and participating in carotenoid metabolism in Arabidopsis leaves and tomato fruits, our investigation marks the first exploration of its function in storage organs lacking a photosynthetic system. Through our research, we validated the existence of plastid-localized ZmPTOX1, existing as a homomultimer, and established its interaction with ferredoxin-NADP+ oxidoreductase 1 (ZmFNR1), a crucial component of the electron transport chain (ETC). This interaction contributes to the maintenance of redox equilibrium within plastids. Our findings indicate a propensity for excessive accumulation of reactive oxygen species (ROS) in wk3735 seeds. Beyond its known role in carotenoids' antioxidant properties, ZmPTOX1 also impacts ROS homeostasis owing to its oxidizing function. Altogether, our results underscore the critical involvement of ZmPTOX1 in governing seed development and germination by preserving redox balance within the seed plastids.

GhiPLATZ17 and GhiPLATZ22, zinc-dependent DNA-binding transcription factors, promote salt tolerance in upland cotton

KEY MESSAGE

The utilization of transcriptome analysis, functional validation, VIGS, and DAB techniques have provided evidence that GhiPLATZ17 and GhiPLATZ22 play a pivotal role in improving the salt tolerance of upland cotton. PLATZ (Plant AT-rich sequences and zinc-binding proteins) are known to be key regulators in plant growth, development, and response to salt stress. In this study, we comprehensively analyzed the PLATZ family in ten cotton species in response to salinity stress. Gossypium herbaceum boasts 25 distinct PLATZ genes, paralleled by 24 in G. raimondii, 25 in G. arboreum, 46 in G. hirsutum, 48 in G. barbadense, 43 in G. tomentosum, 67 in G. mustelinum, 60 in G. darwinii, 46 in G. ekmanianum, and a total of 53 PLATZ genes attributed to G. stephensii. The PLATZ gene family shed light on the hybridization and allopolyploidy events that occurred during the evolutionary history of allotetraploid cotton. Ka/Ks analysis suggested that the PLATZ gene family underwent intense purifying selection during cotton evolution. Analysis of synteny and gene collinearity revealed a complex pattern of segmental and dispersed duplication events to expand PLATZ genes in cotton. Cis-acting elements and gene expressions revealed that GhiPLATZ exhibited salt stress resistance. Transcriptome analysis, functional validation, virus-induced gene silencing (VIGS), and diaminobenzidine staining (DAB) demonstrated that GhiPLATZ17 and GhiPLATZ22 enhance salt tolerance in upland cotton. The study can potentially advance our understanding of identifying salt-resistant genes in cotton.

Comparative analysis of PLATZ transcription factors in six poplar species and analysis of the role of PtrPLATZ14 in leaf development

Plant AT-rich sequence and zinc-binding (PLATZ) proteins are a class of plant-specific transcription factor that play a crucial role in plant growth, development, and stress response. However, the evolutionary relationship of the PLATZ gene family across the Populus genus and the biological functions of the PLATZ protein require further investigation. In this study, we identified 133 PLATZ genes from six Populus species belonging to four Populus sections. Synteny analysis of the PLATZ gene family indicated that whole genome duplication events contributed to the expansion of the PLATZ family. Among the nine paralogous pairs, the protein structure of PtrPLATZ14/18 pair exhibited significant differences with others. Through gene expression patterns and co-expression networks, we discovered divergent expression patterns and sub-networks, and found that the members of pair PtrPLATZ14/18 might play different roles in the regulation of macromolecule biosynthesis and modification. Furthermore, we found that PtrPLATZ14 regulates poplar leaf development by affecting cell size control genes PtrGRF/GIF and PtrTCP. In conclusion, our study provides a theoretical foundation for exploring the evolution relationships and functions of the PLATZ gene family within Populus species and provides insights into the function and potential mechanism of PtrPLATZ14 in leaf morphology that were diverse across the Populus genus.

Decoding the gene regulatory network of endosperm differentiation in maize

The persistent cereal endosperm constitutes the majority of the grain volume. Dissecting the gene regulatory network underlying cereal endosperm development will facilitate yield and quality improvement of cereal crops. Here, we use single-cell transcriptomics to analyze the developing maize (Zea mays) endosperm during cell differentiation. After obtaining transcriptomic data from 17,022 single cells, we identify 12 cell clusters corresponding to five endosperm cell types and revealing complex transcriptional heterogeneity. We delineate the temporal gene-expression pattern from 6 to 7 days after pollination. We profile the genomic DNA-binding sites of 161 transcription factors differentially expressed between cell clusters and constructed a gene regulatory network by combining the single-cell transcriptomic data with the direct DNA-binding profiles, identifying 181 regulons containing genes encoding transcription factors along with their high-confidence targets, Furthermore, we map the regulons to endosperm cell clusters, identify cell-cluster-specific essential regulators, and experimentally validated three predicted key regulators. This study provides a framework for understanding cereal endosperm development and function at single-cell resolution.

Evidence for poplar PtaPLATZ18 in the regulation of plant growth and vascular tissues development

Introduction

Plant A/T-rich protein and zinc-binding protein (PLATZ) are plant-specific transcription factors playing a role in plant development and stress response. To assess the role of PLATZs in vascular system development and wood formation in poplar, a functional study for PtaPLATZ18, whose expression was associated with the xylem, was carried out.

Methods

Poplar dominant repressor lines for PtaPLATZ18 were produced by overexpressing a PtaPLATZ18-SRDX fusion. The phenotype of three independent transgenic lines was evaluated at morphological, biochemical, and molecular levels and compared to the wild type.

Results

The PtaPLATZ18-SRDX lines showed increased plant height resulting from higher internode length. Besides, a higher secondary xylem thickness was also evidenced in these dominant repression lines as compared to the wild type suggesting an activation of cambial activity. A higher amount of lignin was evidenced within wood tissue as compared to the wild type, indicating an alteration in cell wall composition within xylem cell types. This latter phenotype was linked to an increased expression of genes involved in lignin biosynthesis and polymerization.

Discussion

The phenotype observed in the PtaPLATZ18-SRDX lines argues that this transcription factor targets key regulators of plant growth and vascular tissues development.

Global analysis of seed transcriptomes reveals a novel PLATZ regulator for seed size and weight control in soybean

Seed size and weight are important factors that influence soybean yield. Combining the weighted gene co-expression network analysis (WGCNA) of 45 soybean accessions and gene dynamic changes in seeds at seven developmental stages, we identified candidate genes that may control the seed size/weight. Among these, a PLATZ-type regulator overlapping with 10 seed weight QTLs was further investigated. This zinc-finger transcriptional regulator, named as GmPLATZ, is required for the promotion of seed size and weight in soybean. The GmPLATZ may exert its functions through direct binding to the promoters and activation of the expression of cyclin genes and GmGA20OX for cell proliferation. Overexpression of the GmGA20OX enhanced seed size/weight in soybean. We further found that the GmPLATZ binds to a 32-bp sequence containing a core palindromic element AATGCGCATT. Spacing of the flanking sequences beyond the core element facilitated GmPLATZ binding. An elite haplotype Hap3 was also identified to have higher promoter activity and correlated with higher gene expression and higher seed weight. Orthologues of the GmPLATZ from rice and Arabidopsis play similar roles in seeds. Our study reveals a novel module of GmPLATZ-GmGA20OX/cyclins in regulating seed size and weight and provides valuable targets for breeding of crops with desirable agronomic traits.

Transcriptome-wide identification and characterization of genes exhibit allele-specific imprinting in maize embryo and endosperm

BACKGROUND

Genomic imprinting refers to a subset of genes that are expressed from only one parental allele during seed development in plants. Studies on genomic imprinting have revealed that intraspecific variations in genomic imprinting expression exist in naturally genetic varieties. However, there have been few studies on the functional analysis of allele-specific imprinted genes.

RESULTS

Here, we generated three reciprocal crosses among the B73, Mo17 and CAU5 inbred lines. Based on the transcriptome-wide analysis of allele-specific expression using RNA sequencing technology, 305 allele-specific imprinting genes (ASIGs) were identified in embryos, and 655 ASIGs were identified in endosperms from three maize F1 hybrids. Of these ASIGs, most did not show consistent maternal or paternal bias between the same tissue from different hybrids or different tissues from one hybrid cross. By gene ontology (GO) analysis, five and eight categories of GO exhibited significantly higher functional enrichments for ASIGs identified in embryo and endosperm, respectively. These functional categories indicated that ASIGs are involved in intercellular nutrient transport, signaling pathways, and transcriptional regulation of kernel development. Finally, the mutation and overexpression of one ASIG (Zm305) affected the length and width of the kernel.

CONCLUSION

In this study, our data will be helpful in gaining further knowledge of genes exhibiting allele-specific imprinting patterns in seeds. The gain- and loss-of-function phenotypes of ASIGs associated with agronomically important seed traits provide compelling evidence for ASIGs as crucial targets to optimize seed traits in crop plants.

Control of cellularization, nuclear localization, and antipodal cell cluster development in maize embryo sacs

The maize female gametophyte contains four cell types: two synergids, an egg cell, a central cell, and a variable number of antipodal cells. In maize, these cells are produced after three rounds of free-nuclear divisions followed by cellularization, differentiation, and proliferation of the antipodal cells. Cellularization of the eight-nucleate syncytium produces seven cells with two polar nuclei in the central cell. Nuclear localization is tightly controlled in the embryo sac. This leads to precise allocation of the nuclei into the cells upon cellularization. Nuclear positioning within the syncytium is highly correlated with their identity after cellularization. Two mutants are described with extra polar nuclei, abnormal antipodal cell morphology, and reduced antipodal cell number, as well as frequent loss of antipodal cell marker expression. Mutations in one of these genes, indeterminate gametophyte2 encoding a MICROTUBULE ASSOCIATED PROTEIN65-3 homolog, shows a requirement for MAP65-3 in cellularization of the syncytial embryo sac as well as for normal seed development. The timing of the effects of ig2 suggests that the identity of the nuclei in the syncytial female gametophyte can be changed very late before cellularization.

Whole-genome identification and multiple abiotic stresses expression pattern profiling analysis of PLATZ transcription factor family members in Pecan (Carya illinoensis)

Plant AT-rich sequence and zinc-binding (PLATZ), as a plant-specific transcription factor, have been identified and studied in a variety of plants. However, there are no reports about PLATZ proteins in Carya illinoensis (pecan). Here, 24 C. illinoensis CiPLATZs have been identified and divided into 4 groups. Gene structure, motif composition, conserved domain and cis-acting elements analysis indicated that the PLATZ gene family was highly conserved. Transcriptome data combined with qRT-PCR analysis revealed that CiPLATZ6, CiPLATZ12, CiPLATZ13, CiPLATZ14 and CiPLATZ23 were highly expressed in multiple tissues of C. illinoensis and strongly responded to drought, salt and heat stress. Among them, CiPLATZ6, CiPLATZ12 and CiPLATZ23 were all located in the nucleus and had no transcriptional autoactivation ability in yeast cells, and acted as transcriptional suppressors in plants. In addition, the CiPLATZ23-overexpressing transgenic Arabidopsis thaliana showed enhanced tolerance to drought. Measurements of physiological indicators and analysis of stress-related genes expression levels in transgenic A. thaliana were used to support this conclusion. The results of this study are helpful to understand the structural feature and function of CiPLATZs, and provide candidate genes for molecular breeding of drought tolerance of C. illinoensis.

RNA polymerase common subunit ZmRPABC5b is transcriptionally activated by Opaque2 and essential for endosperm development in maize

Maize (Zea mays) kernel size is an important factor determining grain yield; although numerous genes regulate kernel development, the roles of RNA polymerases in this process are largely unclear. Here, we characterized the defective kernel 701 (dek701) mutant that displays delayed endosperm development but normal vegetative growth and flowering transition, compared to its wild type. We cloned Dek701, which encoded ZmRPABC5b, a common subunit to RNA polymerases I, II and III. Loss-of-function mutation of Dek701 impaired the function of all three RNA polymerases and altered the transcription of genes related to RNA biosynthesis, phytohormone response and starch accumulation. Consistent with this observation, loss-of-function mutation of Dek701 affected cell proliferation and phytohormone homeostasis in maize endosperm. Dek701 was transcriptionally regulated in the endosperm by the transcription factor Opaque2 through binding to the GCN4 motif within the Dek701 promoter, which was subjected to strong artificial selection during maize domestication. Further investigation revealed that DEK701 interacts with the other common RNA polymerase subunit ZmRPABC2. The results of this study provide substantial insight into the Opaque2-ZmRPABC5b transcriptional regulatory network as a central hub for regulating endosperm development in maize.

AGAMOUS regulates various target genes via cell cycle-coupled H3K27me3 dilution in floral meristems and stamens

The MADS domain transcription factor AGAMOUS (AG) regulates floral meristem termination by preventing maintenance of the histone modification lysine 27 of histone H3 (H3K27me3) along the KNUCKLES (KNU) coding sequence. At 2 d after AG binding, cell division has diluted the repressive mark H3K27me3, allowing activation of KNU transcription prior to floral meristem termination. However, how many other downstream genes are temporally regulated by this intrinsic epigenetic timer and what their functions are remain unknown. Here, we identify direct AG targets regulated through cell cycle-coupled H3K27me3 dilution in Arabidopsis thaliana. Expression of the targets KNU, AT HOOK MOTIF NUCLEAR LOCALIZED PROTEIN18 (AHL18), and PLATZ10 occurred later in plants with longer H3K27me3-marked regions. We established a mathematical model to predict timing of gene expression and manipulated temporal gene expression using the H3K27me3-marked del region from the KNU coding sequence. Increasing the number of del copies delayed and reduced KNU expression in a polycomb repressive complex 2- and cell cycle-dependent manner. Furthermore, AHL18 was specifically expressed in stamens and caused developmental defects when misexpressed. Finally, AHL18 bound to genes important for stamen growth. Our results suggest that AG controls the timing of expression of various target genes via cell cycle-coupled dilution of H3K27me3 for proper floral meristem termination and stamen development.

Genome-wide characterization of the PLATZ gene family in watermelon (Citrullus lanatus L.) with putative functions in biotic and abiotic stress response

Plant AT-rich sequence and zinc-binding (PLATZ) proteins are plant-specific transcription factors involved in growth, development, and stress responses. Here, we conducted a genome-wide characterization of the watermelon ClPLATZ family and examined its expression responsiveness to defense hormones and pathogen infection along with putative functions in biotic and abiotic stress responses. The watermelon genome contains 12 putative ClPLATZ genes, encoding proteins with a characteristic PLATZ domain, and their promoters contain various cis-elements related to plant growth, development, phytohormones and stress response. The ClPLATZ genes, except ClPLATZ6, are differentially expressed in response to defense hormones (e.g., salicylic acid and methyl jasmonate) and fungal infections caused by Fusarium oxysporum f. sp. niveum and Stagonosporopsis cucurbitacearum. Most ClPLATZ proteins interact with other proteins (viz., ClDP, ClRPT2a, and ClRPC53). Among ClPLATZ proteins, ClPLATZ8, 9, 10, and 11 are predominately localized in the nucleus. ClPLATZ3 and 8 positively, but ClPLATZ11 negatively regulate resistance against Pseudomonas syringe pv. tomato DC3000 in transgenic Arabidopsis lines. ClPLATZ8 and 11 positively regulate stress tolerance to NaCl and mannitol during seed germination in transgenic Arabidopsis. In conclusion, the characterization of the ClPLATZ family provides insights into the biological functions of ClPLATZ genes in growth, development, and stress response in watermelon. Further, the involvement of certain ClPLATZ genes in biotic and abiotic stress response in transgenic Arabidopsis suggests their potential application in engineering stress-tolerant crops.

Genome-Wide Identification and Expression Analysis of the PLATZ Transcription Factor in Tomato

The PLATZ (plant AT protein and zinc-binding protein) transcription factor family is involved in the regulation of plant growth and development and plant stress response. In this study, 24 SlPLATZs were identified from the cultivated tomato genome and classified into four groups based on the similarity of conserved patterns among members of the same subfamily. Fragment duplication was an important way to expand the SlPLATZ gene family in tomatoes, and the sequential order of tomato PLATZ genes in the evolution of monocotyledonous and dicotyledonous plants and the roles they played were hypothesized. Expression profiles based on quantitative real-time reverse transcription PCR showed that SlPLATZ was involved in the growth of different tissues in tomatoes. SlPLATZ21 acts mainly in the leaves. SlPLATZ9, SlPLATZ21, and SlPLATZ23 were primarily involved in the red ripening, expanding, and mature green periods of fruit, respectively. In addition, SlPLATZ1 was found to play an important role in salt stress. This study will lay the foundation for the analysis of the biological functions of SlPLATZ genes and will also provide a theoretical basis for the selection and breeding of new tomato varieties and germplasm innovation.

Genome-wide analysis of MdPLATZ genes and their expression during axillary bud outgrowth in apple (Malus domestica Borkh.)

BACKGROUND

Branching is a plastic character that affects plant architecture and spatial structure. The trait is controlled by a variety of plant hormones through coordination with environmental signals. Plant AT-rich sequence and zinc-binding protein (PLATZ) is a transcription factor that plays an important role in plant growth and development. However, systematic research on the role of the PLATZ family in apple branching has not been conducted previously.

RESULTS

In this study, a total of 17 PLATZ genes were identified and characterized from the apple genome. The 83 PLATZ proteins from apple, tomato, Arabidopsis, rice, and maize were classified into three groups based on the topological structure of the phylogenetic tree. The phylogenetic relationships, conserved motifs, gene structure, regulatory cis-acting elements, and microRNAs of the MdPLATZ family members were predicted. Expression analysis revealed that MdPLATZ genes exhibited distinct expression patterns in different tissues. The expression patterns of the MdPLATZ genes were systematically investigated in response to treatments that impact apple branching [thidazuron (TDZ) and decapitation]. The expression of MdPLATZ1, 6, 7, 8, 9, 15, and 16 was regulated during axillary bud outgrowth based on RNA-sequencing data obtained from apple axillary buds treated by decapitation or exogenous TDZ application. Quantitative real-time PCR analysis showed that MdPLATZ6 was strongly downregulated in response to the TDZ and decapitation treatments, however, MdPLATZ15 was significantly upregulated in response to TDZ, but exhibited little response to decapitation. Furthermore, the co-expression network showed that PLATZ might be involved in shoot branching by regulating branching-related genes or mediating cytokinin or auxin pathway.

CONCLUSION

The results provide valuable information for further functional investigation of MdPLATZ genes in the control of axillary bud outgrowth in apple.

The RhWRKY33a-RhPLATZ9 regulatory module delays petal senescence by suppressing rapid reactive oxygen species accumulation in rose flowers

Redox homeostasis in plant cells is critical for maintaining normal growth and development because reactive oxygen species (ROS) can function as signaling molecules or toxic compounds. However, how plants fine-tune redox homeostasis during natural or stress-induced senescence remains unclear. Cut roses (Rosa hybrida), an economically important ornamental product worldwide, often undergo stress-induced precocious senescence at the post-harvest bud stage. Here, we identified RhPLATZ9, an age- and dehydration-induced PLATZ (plant AT-rich sequence and zinc-binding) protein, and determined that it functions as a transcriptional repressor in rose flowers during senescence. We also showed that RhWRKY33a regulates RhPLATZ9 expression during flower senescence. RhPLATZ9-silenced flowers and RhWRKY33a-silenced flowers showed accelerated senescence, with higher ROS contents than the control. By contrast, overexpression of RhWRKY33a or RhPLATZ9 delayed flower senescence, and overexpression in rose calli showed lower ROS accumulation than the control. RNA-sequencing analysis revealed that apoplastic NADPH oxidase genes (RhRbohs) were enriched among the upregulated differentially expressed genes in RhPLATZ9-silenced flowers compared to wild-type flowers. Yeast one-hybrid assays, electrophoretic mobility shift assays, dual luciferase assays and chromatin immunoprecipitation quantitative PCR confirmed that the RhRbohD gene is a direct target of RhPLATZ9. These findings suggest that the RhWRKY33a-RhPLATZ9-RhRbohD regulatory module acts as a brake to help maintain ROS homeostasis in petals and thus antagonize age- and stress-induced precocious senescence in rose flowers.

Regulation of drought tolerance in Arabidopsis involves the PLATZ4-mediated transcriptional repression of plasma membrane aquaporin PIP2;8

Plant A/T-rich protein and zinc-binding protein (PLATZ) transcription factors play important roles in plant growth, development and abiotic stress responses. However, how PLATZ influences plant drought tolerance remains poorly understood. The present study showed that PLATZ4 increased drought tolerance in Arabidopsis thaliana by causing stomatal closure. Transcriptional profiling analysis revealed that PLATZ4 affected the expression of a set of genes involved in water and ion transport, antioxidant metabolism, small peptides and abscisic acid (ABA) signaling. Among these genes, the direct binding of PLATZ4 to the A/T-rich sequences in the plasma membrane intrinsic protein 2;8 (PIP2;8) promoter was identified. PIP2;8 consistently reduced drought tolerance in Arabidopsis through inhibiting stomatal closure. PIP2;8 was localized in the plasma membrane, exhibited water channel activity in Xenopus laevis oocytes and acted epistatically to PLATZ4 in regulating the drought stress response in Arabidopsis. PLATZ4 increased ABA sensitivity through upregulating the expression of ABSCISIC ACID INSENSITIVE 3 (ABI3), ABI4 and ABI5. The transcripts of PLATZ4 were induced to high levels in vegetative seedlings under drought and ABA treatments within 6 and 3 h, respectively. Collectively, these findings reveal that PLATZ4 positively influences plant drought tolerance through regulating the expression of PIP2;8 and genes involved in ABA signaling.

A translatome-transcriptome multi-omics gene regulatory network reveals the complicated functional landscape of maize

BACKGROUND

Maize (Zea mays L.) is one of the most important crops worldwide. Although sophisticated maize gene regulatory networks (GRNs) have been constructed for functional genomics and phenotypic dissection, a multi-omics GRN connecting the translatome and transcriptome is lacking, hampering our understanding and exploration of the maize regulatome.

RESULTS

We collect spatio-temporal translatome and transcriptome data and systematically explore the landscape of gene transcription and translation across 33 tissues or developmental stages of maize. Using this comprehensive transcriptome and translatome atlas, we construct a multi-omics GRN integrating mRNAs and translated mRNAs, demonstrating that translatome-related GRNs outperform GRNs solely using transcriptomic data and inter-omics GRNs outperform intra-omics GRNs in most cases. With the aid of the multi-omics GRN, we reconcile some known regulatory networks. We identify a novel transcription factor, ZmGRF6, which is associated with growth. Furthermore, we characterize a function related to drought response for the classic transcription factor ZmMYB31.

CONCLUSIONS

Our findings provide insights into spatio-temporal changes across maize development at both the transcriptome and translatome levels. Multi-omics GRNs represent a useful resource for dissection of the regulatory mechanisms underlying phenotypic variation.

E3 ubiquitin ligase OsPIE3 destabilises the B-lectin receptor-like kinase PID2 to control blast disease resistance in rice

Previous studies have reported that PID2, which encodes a B-lectin receptor-like kinase, is a key gene in the resistance of rice to Magnaporthe oryzae strain ZB15. However, the PID2-mediated downstream signalling events remain largely unknown. The U-box E3 ubiquitin ligase OsPIE3 (PID2-interacting E3) was isolated and confirmed to play key roles in PID2-mediated rice blast resistance. Yeast two-hybrid analysis showed that the armadillo repeat region of OsPIE3 is required for its interaction with PID2. Further investigation demonstrated that OsPIE3 can modify the subcellular localisation of PID2, thus promoting its nuclear recruitment from the plasma membrane for protein degradation in the ubiquitin-proteasome system. Site-directed mutagenesis of a conserved cysteine site (C230S) within the U-box domain of OsPIE3 reduces PID2 translocation and ubiquitination. Genetic analysis suggested that OsPIE3 loss-of-function mutants exhibited enhanced resistance to M. oryzae isolate ZB15, whereas mutants with overexpressed OsPIE3 exhibited reduced resistance. Furthermore, the OsPIE3/PID2-double mutant displayed a similar blast phenotype to that of the PID2 single mutant, suggesting that OsPIE3 is a negative regulator and functions along with PID2 in blast disease resistance. Our findings confirm that the E3 ubiquitin ligase OsPIE3 is necessary for PID2-mediated rice blast disease resistance regulation.

Genome-wide identification of PLATZ genes related to cadmium tolerance in Populus trichocarpa and characterization of the role of PtPLATZ3 in phytoremediation of cadmium

Plant AT-rich sequence and zinc-binding (PLATZ) proteins are a class of plant-specific zinc finger transcription factors that perform critical functions in plant development and resistance. However, the function of PLATZs in heavy metal tolerance has not yet been investigated. Moreover, only a few PLATZ proteins have been functionally characterized in tree species. In this study, we identified 18 PtPLATZ genes in Populus trichocarpa, an important woody model plant, and classified them into five groups. PtPLATZ genes attributed to the same clade usually possess similar exon-intron structures containing two or three introns, as well as a similar motif composition. Furthermore, chromosomal location analysis indicated an uneven distribution of PtPLATZ genes on 13 of the 19 Populus chromosomes. Promoter cis-acting element prediction and gene expression analysis showed that PtPLATZ genes were highly responsive to heavy metal stress. Heterologous yeast expression revealed that PtPLATZ1, PtPLATZ2, PtPLATZ3, PtPLATZ4, PtPLATZ8 and PtPLATZ9 are significantly involved in Cd tolerance. In addition, transgenic expression of PtPLATZ3 significantly enhanced Cd tolerance and accumulation, slowed the decline in chlorophyll content, maintained membrane integrity in Populus, and increased the expression of genes related to Cd tolerance and accumulation. In conclusion, our results suggest the potential of PtPLATZ3 to improve Cd tolerance and accumulation in Populus, which is of great significance for phytoremediation.

Genome-Wide Identification and Phylogenetic and Expression Analyses of the PLATZ Gene Family in Medicago sativa L

The PLATZ family is a novel class of plant-specific zinc finger transcription factors with important roles in plant growth and development and abiotic stress responses. PLATZ members have been identified in many plants, including Oryza sativa, Zea mays, Triticum aestivum, Fagopyrum tataricum, and Arabidopsis thaliana; however, due to the complexity of the alfalfa reference genome, the members of the PLATZ gene family in alfalfa (Medicago sativa L.) have not been systematically identified and analyzed. In this study, 55 Medicago sativa PLATZ genes (MsPLATZs) were identified in the alfalfa "Xinjiangdaye" reference genome. Basic bioinformatic analysis was performed, including the characterization of sequence lengths, protein molecular weights, genomic positions, and conserved motifs. Expression analysis reveals that 7 MsPLATZs are tissue-specifically expressed, and 10 MsPLATZs are expressed in all examined tissues. The transcriptomic expression of these genes is obvious, indicating that these MsPLATZs have different functions in the growth and development of alfalfa. Based on transcriptome data analysis and real-time quantitative PCR (RT-qPCR), we identified 22, 22, and 21 MsPLATZ genes that responded to salt, cold, and drought stress, respectively, with 20 MsPLATZs responding to all three stresses. This study lays a foundation for further exploring the functions of MsPLATZs, and provides ideas for the improvement of alfalfa varieties and germplasm innovation.

Identification of PLATZ genes in Malus and expression characteristics of MdPLATZs in response to drought and ABA stresses

Plant AT-rich sequences and zinc-binding proteins (PLATZ) play crucial roles in response to environmental stresses. Nevertheless, PLATZ gene family has not been systemically studied in Rosaceae species, such as in apple, pear, peach, or strawberry. In this study, a total of 134 PLATZ proteins were identified from nine Rosaceae genomes and were classified into seven phylogenetic groups. Subsequently, the chromosomal localization, duplication, and collinearity relationship for apple PLATZ genes were investigated, and segmental duplication is a major driving-force in the expansion of PLATZ in Malus. Expression profiles analysis showed that PLATZs had distinct expression patterns in different tissues, and multiple genes were significantly changed after drought and ABA treatments. Furthermore, the co-expression network combined with RNA-seq data showed that PLATZ might be involved in drought stress by regulating ABA signaling pathway. In summary, this study is the first in-depth and systematic identification of PLATZ gene family in Rosaceae species, especially for apple, and provided specific PLATZ gene resource for further functional research in response to abiotic stress.

A Systemic Investigation of Genetic Architecture and Gene Resources Controlling Kernel Size-Related Traits in Maize

Grain yield is the most critical and complex quantitative trait in maize. Kernel length (KL), kernel width (KW), kernel thickness (KT) and hundred-kernel weight (HKW) associated with kernel size are essential components of yield-related traits in maize. With the extensive use of quantitative trait locus (QTL) mapping and genome-wide association study (GWAS) analyses, thousands of QTLs and quantitative trait nucleotides (QTNs) have been discovered for controlling these traits. However, only some of them have been cloned and successfully utilized in breeding programs. In this study, we exhaustively collected reported genes, QTLs and QTNs associated with the four traits, performed cluster identification of QTLs and QTNs, then combined QTL and QTN clusters to detect consensus hotspot regions. In total, 31 hotspots were identified for kernel size-related traits. Their candidate genes were predicted to be related to well-known pathways regulating the kernel developmental process. The identified hotspots can be further explored for fine mapping and candidate gene validation. Finally, we provided a strategy for high yield and quality maize. This study will not only facilitate causal genes cloning, but also guide the breeding practice for maize.

Comprehensive Genome-Wide Analysis and Expression Pattern Profiling of PLATZ Gene Family Members in Solanum Lycopersicum L. under Multiple Abiotic Stresses

PLATZ (plant AT-rich sequence and zinc-binding) family proteins with two conserved zinc-dependent DNA-binding motifs are transcription factors specific to the plant kingdom. The functions of PLATZ proteins in growth, development, and adaptation to multiple abiotic stresses have been investigated in various plant species, but their role in tomato has not been explored yet. In the present work, 20 non-redundant Solanum lycopersicum PLATZ (SlPLATZ) genes with three segmentally duplicated gene pairs and four tandemly duplicated gene pairs were identified on eight tomato chromosomes. The comparative modeling and gene ontology (GO) annotations of tomato PLATZ proteins indicated their probable roles in defense response, transcriptional regulation, and protein metabolic processes as well as their binding affinity for various ligands, including nucleic acids, peptides, and zinc. SlPLATZ10 and SlPLATZ17 were only expressed in 1 cm fruits and flowers, respectively, indicating their preferential involvement in the development of these organs. The expression of SlPLATZ1, SlPLATZ12, and SlPLATZ19 was up- or down-regulated following exposure to various abiotic stresses, whereas that of SlPLATZ11 was induced under temperature stresses (i.e., cold and heat stress), revealing their probable function in the abiotic stress tolerance of tomato. Weighted gene co-expression network analysis corroborated the aforementioned findings by spotlighting the co-expression of several stress-associated genes with SlPLATZ genes. Confocal fluorescence microscopy revealed the localization of SlPLATZ−GFP fusion proteins in the nucleus, hinting at their functions as transcription factors. These findings provide a foundation for a better understanding of the structure and function of PLATZ genes and should assist in the selection of potential candidate genes involved in the development and abiotic stress adaptation in tomato.

Uncovering the genetic basis of gluten aggregation parameters by genome-wide association analysis in wheat (Triticum aestivum L.) using GlutoPeak

BACKGROUND

Numerous studies have shown that gluten aggregation properties directly affect the processing quality of wheat, however, the genetic basis of gluten aggregation properties were rarely reported.

RESULTS

To explore the genetic basis of gluten aggregation properties in wheat, an association population consisted with 207 wheat genotypes were constructed for evaluating nine parameters of aggregation properties on GlutoPeak across three-year planting seasons. A total of 940 significant SNPs were detected for 9 GlutoPeak parameters through genome-wide association analysis (GWAS). Finally, these SNPs were integrated to 68 non-redundant QTL distributed on 20 chromosomes and 54 QTL was assigned as pleiotropic loci which accounting for multiple parameters of gluten aggregation property. Furthermore, the peak SNPs representing 54 QTL domonstrated additive effect on all the traits. There was a significant positive correlation between the number of favorable alleles and the phenotypic values of each parameter. Peak SNPs of two novel QTL, q3AL.2 and q4DL, which contributing to both PMT (peak maximum time) and A3 (area from the first minimum to torque 15 s before the maximum torque) parameters, were selected for KASP (Kompetitive Allele Specific PCR) markers development and the KASP markers can be used for effectively evaluating the quality of gluten aggregation properties in the association population.

CONCLUSION

The rapid and efficient GlutoPeak method for gluten measurement can be used for early selection of wheat breeding. This study revealed the genetic loci related to GlutoPeak parameters in association population, which would be helpful to develop wheat elite lines with improved gluten aggregation through molecular marker-assisted breeding.

Histone acetyltransferase TaHAG1 interacts with TaPLATZ5 to activate TaPAD4 expression and positively contributes to powdery mildew resistance in wheat

Plants have evolved a two-branched innate immune system to detect and cope with pathogen attack, which are initiated by cell-surface and intracellular immune receptors leading to pattern-triggered immunity (PTI) and effector-triggered immunity (ETI), respectively. A core transducer including PAD4-EDS1 node is proposed as the convergence point for a two-tiered immune system in conferring pathogen immunity. However, the transcriptional regulatory mechanisms controlling expression of these key transducers remain largely unknown. Here, we identified histone acetyltransferase TaHAG1 as a positive regulator of powdery mildew resistance in wheat. TaHAG1 regulates expression of key transducer gene TaPAD4 and promotes SA and reactive oxygen species accumulation to accomplish resistance to Bgt infection. Moreover, overexpression and CRISPR-mediated knockout of TaPAD4 validate its role in wheat powdery mildew resistance. Furthermore, TaHAG1 physically interacts with TaPLATZ5, a plant-specific zinc-binding protein. TaPLATZ5 directly binds to promoter of TaPAD4 and together with TaHAG1 to potentiate the expression of TaPAD4 by increasing the levels of H3 acetylation. Our study revealed a key transcription regulatory node in which TaHAG1 acts as an epigenetic modulator and interacts with TaPLATZ5 that confers powdery mildew resistance in wheat through activating a convergence point gene between PTI and ETI, which could be effective for genetic improvement of disease resistance in wheat and other crops.

Paternal imprinting of dosage-effect defective1 contributes to seed weight xenia in maize

Historically, xenia effects were hypothesized to be unique genetic contributions of pollen to seed phenotype, but most examples represent standard complementation of Mendelian traits. We identified the imprinted dosage-effect defective1 (ded1) locus in maize (Zea mays) as a paternal regulator of seed size and development. Hypomorphic alleles show a 5–10% seed weight reduction when ded1 is transmitted through the male, while homozygous mutants are defective with a 70–90% seed weight reduction. Ded1 encodes an R2R3-MYB transcription factor expressed specifically during early endosperm development with paternal allele bias. DED1 directly activates early endosperm genes and endosperm adjacent to scutellum cell layer genes, while directly repressing late grain-fill genes. These results demonstrate xenia as originally defined: Imprinting of Ded1 causes the paternal allele to set the pace of endosperm development thereby influencing grain set and size.

Xenia effects describe the genetic contribution of pollen to seed phenotypes. Here the authors show that paternal imprinting of Ded1 contributes to the xenia effect in maize by setting the pace of endosperm development.

PhePLATZ1, a PLATZ transcription factor in moso bamboo (Phyllostachys edulis), improves drought resistance of transgenic Arabidopsis thaliana

Drought is one of the most serious environmental stresses. Plant AT-rich sequence and zinc-binding (PLATZ) proteins perform indispensable functions to regulate plant growth and development and to respond to environmental stress. In this present study, we identified PhePLATZ1 in moso bamboo and found that its expression was up-regulated in response to 20% PEG-6000 and abscisic acid (ABA) treatments. Next, transgenic PhePLATZ1-overexpressing Arabidopsis lines were generated. Overexpression of PhePLATZ1 improved drought stress resistance of transgenic plants by mediating osmotic regulation, enhancing water retention capacity and reducing membrane and oxidative damage. These findings were corroborated by analysing physiological indicators including chlorophyll, relative water content, leaf water loss rate, electrolyte leakage, H₂O₂, proline, malondialdehyde content and the enzyme activities of peroxidase and catalase. Subsequent seed germination and seedling root length experiments that included exposure to exogenous ABA treatments showed that ABA sensitivity decreased in transgenic plants relative to wild-type plants. Moreover, transgenic PhePLATZ1-overexpressing plants promoted stomatal closure in response to ABA treatment, suggesting that PhePLATZ1 might play a positive regulatory role in the drought resistance of plants via the ABA signaling pathway. In addition, the transgenic PhePLATZ1-OE plants showed altered expression of some stress-related genes when grown under drought conditions. Taken together, these findings improve our understanding of the drought response of moso bamboo and provide a key candidate gene for the molecular breeding of this species for drought tolerance.

The PGS1 basic helix-loop-helix protein regulates Fl3 to impact seed growth and grain yield in cereals

Plant transcription factors (TFs), such as basic helix-loop-helix (bHLH) and AT-rich zinc-binding proteins (PLATZ), play critical roles in regulating the expression of developmental genes in cereals. We identified the bHLH protein TaPGS1 (T. aestivum Positive Regulator of Grain Size 1) specifically expressed in the seeds at 5-20 days post-anthesis in wheat. TaPGS1 was ectopically overexpressed (OE) in wheat and rice, leading to increased grain weight (up to 13.81% in wheat and 18.55% in rice lines) and grain size. Carbohydrate and total protein levels also increased. Scanning electron microscopy results indicated that the starch granules in the endosperm of TaPGS1 OE wheat and rice lines were smaller and tightly embedded in a proteinaceous matrix. Furthermore, TaPGS1 was bound directly to the E-box motif at the promoter of the PLATZ TF genes TaFl3 and OsFl3 and positively regulated their expression in wheat and rice. In rice, the OsFl3 CRISPR/Cas9 knockout lines showed reduced average thousand-grain weight, grain width, and grain length in rice. Our results reveal that TaPGS1 functions as a valuable trait-associated gene for improving cereal grain yield.

Genome-Wide Identification of PLATZ Transcription Factors in Ginkgo biloba L. and Their Expression Characteristics During Seed Development

Plant AT-rich protein and zinc-binding protein (PLATZ) is a class of plant-specific zinc-dependent DNA-binding protein that binds to A/T-rich DNA sequences. PLATZ plays an important role in seed development, water tolerance, and cell proliferation in early plant growth. In this study, 11 GbPLATZs were identified from the ginkgo genome with complete PLATZ-conserved domains, which represents a smaller number compared with angiosperms. Multi-species phylogenetic analysis showed that PLATZ genes were conserved in seed plants, and the 11 members were represented by four groups, among which groups I and II were closely related. Analysis of gene structures, sequence module characteristics, and expression patterns showed that GbPLATZs were similar within and differed between groups. RNA-seq and qRT-PCR results showed that GbPLATZs had distinct expression patterns. Most genes were associated with seed development, among which six genes were highly related. Subcellular localization experiments showed that six GbPLATZ proteins related to seed development were localized in the nucleus, suggesting that they might function as traditional transcription factors. This study provides a basis for understanding the structural differentiation, evolutionary characteristics, expression profile, and potential functions of PLATZ transcription factors in Ginkgo biloba.

Maize RNA 3'-terminal phosphate cyclase-like protein promotes 18S pre-rRNA cleavage and is important for kernel development

Plant ribosomes contain four specialized ribonucleic acids, the 5S, 5.8S, 18S, and 25S ribosomal RNAs (rRNAs). Maturation of the latter three rRNAs requires cooperative processing of a single transcript by several endonucleases and exonucleases at specific sites. In maize (Zea mays), the exact nucleases and components required for rRNA processing remain poorly understood. Here, we characterized a conserved RNA 3'-terminal phosphate cyclase (RCL)-like protein, RCL1, that functions in 18S rRNA maturation. RCL1 is highly expressed in the embryo and endosperm during early seed development. Loss of RCL1 function resulted in lethality due to aborted embryo cell differentiation. We also observed pleiotropic defects in the rcl1 endosperm, including abnormal basal transfer cell layer growth and aleurone cell identity, and reduced storage reserve accumulation. The rcl1 seeds had lower levels of mature 18S rRNA and the related precursors were altered in abundance compared with wild type. Analysis of transcript levels and protein accumulation in rcl1 revealed that the observed lower levels of zein and starch synthesis enzymes mainly resulted from effects at the transcriptional and translational levels, respectively. These results demonstrate that RCL1-mediated 18S pre-rRNA processing is essential for ribosome function and messenger RNA translation during maize seed development.

ORESARA 15, a PLATZ transcription factor, controls root meristem size through auxin and cytokinin signalling-related pathways

An optimal size of post-embryonic root apical meristem (RAM) is achieved by a balance between cell division and differentiation. Despite extensive research, molecular mechanisms underlying the coordination of cell division and differentiation are still fragmentary. Here, we report that ORESARA 15 (ORE15), an Arabidopsis PLANT A/T-RICH SEQUENCE-AND ZINC-BINDING PROTEIN (PLATZ) transcription factor preferentially expressed in the RAM, determines RAM size. Primary root length, RAM size, cell division rate, and stem cell niche activity were reduced in an ore15 loss-of-function mutant but enhanced in an activation-tagged line overexpressing ORE15, compared with wild type. ORE15 forms mutually positive and negative feedback loops with auxin and cytokinin signalling, respectively. Collectively, our findings imply that ORE15 controls RAM size by mediating the antagonistic interaction between auxin and cytokinin signalling-related pathways.

Genome-wide identification and expression analysis of the plant-specific PLATZ gene family in Tartary buckwheat (Fagopyrum tataricum)

BACKGROUND

Plant AT-rich sequence and zinc-binding (PLATZ) proteins belong to a novel class of plant-specific zinc-finger-dependent DNA-binding proteins that play essential roles in plant growth and development. Although the PLATZ gene family has been identified in several species, systematic identification and characterization of this gene family has not yet been carried out for Tartary buckwheat, which is an important medicinal and edible crop with high nutritional value. The recent completion of Tartary buckwheat genome sequencing has laid the foundation for this study.

RESULTS

A total of 14 FtPLATZ proteins were identified in Tartary buckwheat and were classified into four phylogenetic groups. The gene structure and motif composition were similar within the same group, and evident distinctions among different groups were detected. Gene duplication, particularly segmental duplication, was the main driving force in the evolution of FtPLATZs. Synteny analysis revealed that Tartary buckwheat shares more orthologous PLATZ genes with dicotyledons, particularly soybean. In addition, the expression of FtPLATZs in different tissues and developmental stages of grains showed evident specificity and preference. FtPLATZ3 may be involved in the regulation of grain size, and FtPLATZ4 and FtPLATZ11 may participate in root development. Abundant and variable hormone-responsive cis-acting elements were distributed in the promoter regions of FtPLATZs, and almost all FtPLATZs were significantly regulated after exogenous hormone treatments, particularly methyl jasmonate treatment. Moreover, FtPLATZ6 was significantly upregulated under all exogenous hormone treatments, which may indicate that this gene plays a critical role in the hormone response of Tartary buckwheat.

CONCLUSIONS

This study lays a foundation for further exploration of the function of FtPLATZ proteins and their roles in the growth and development of Tartary buckwheat and contributes to the genetic improvement of Tartary buckwheat.

Identifying mutations in sd1, Pi54 and Pi-ta, and positively selected genes of TN1, the first semidwarf rice in Green Revolution

BACKGROUND

Taichung Native 1 (TN1) is the first semidwarf rice cultivar that initiated the Green Revolution. As TN1 is a direct descendant of the Dee-geo-woo-gen cultivar, the source of the sd1 semidwarf gene, the sd1 gene can be defined through TN1. Also, TN1 is susceptible to the blast disease and is described as being drought-tolerant. However, genes related to these characteristics of TN1 are unknown. Our aim was to identify and characterize TN1 genes related to these traits.

RESULTS

Aligning the sd1 of TN1 to Nipponbare sd1, we found a 382-bp deletion including a frameshift mutation. Sanger sequencing validated this deleted region in sd1, and we proposed a model of the sd1 gene that corrects errors in the literature. We also predicted the blast disease resistant (R) genes of TN1. Orthologues of the R genes in Tetep, a well-known resistant cultivar that is commonly used as a donor for breeding new blast resistant cultivars, were then sought in TN1, and if they were present, we looked for mutations. The absence of Pi54, a well-known R gene, in TN1 partially explains why TN1 is more susceptible to blast than Tetep. We also scanned the TN1 genome using the PosiGene software and identified 11 genes deemed to have undergone positive selection. Some of them are associated with drought-resistance and stress response.

CONCLUSIONS

We have redefined the deletion of the sd1 gene in TN1, a direct descendant of the Dee-geo-woo-gen cultivar, and have corrected some literature errors. Moreover, we have identified blast resistant genes and positively selected genes, including genes that characterize TN1's blast susceptibility and abiotic stress response. These new findings increase the potential of using TN1 to breed new rice cultivars.

The O2-ZmGRAS11 transcriptional regulatory network orchestrates the coordination of endosperm cell expansion and grain filling in maize

Maize (Zea mays) endosperm filling is coordinated with cell expansion to enlarge the grain size, but the mechanism coupling the two processes is poorly understood. Starchy endosperm cells basically contain no visible vacuoles for cell expansion. During grain filling, efficient synthesis of storage compounds leads to reduced cytoplasm and thus lowered cell turgor pressure. Although bioactive gibberellins (GAs) are essential for cell expansion, they accumulate at a low level at this stage. In this study, we identified an endosperm-specific GRAS domain-containing protein (ZmGRAS11) that lacks the DELLA domain and promotes cell expansion in the filling endosperm. The zmgras11 loss-of-function mutants showed normal grain filling but delayed cell expansion, thereby resulting in reduced kernel size and weight. Overexpression of ZmGRAS11 led to larger endosperm cells and therefore increased kernel size and weight. Consistent with this, ZmGRAS11 positively regulates the expression of ZmEXPB12, which is essential for cell expansion, at the endosperm filling stage. Moreover, we found that Opaque2 (O2), a central transcription factor that regulates endosperm filling, could directly bind to the promoter of ZmGRAS11 and activate its expression. Taken together, these results suggest that endosperm cell expansion is coupled with endosperm filling, which is orchestrated by the O2-ZmGRAS11-centered transcriptional regulatory network. Our findings also provide potential targets for maize yield improvement by increasing the storage capacity of endosperm cells.

VviPLATZ1 is a major factor that controls female flower morphology determination in grapevine

Plant genetic sex determinants that mediate the transition to dioecy are predicted to be diverse, as this type of mating system independently evolved multiple times in angiosperms. Wild Vitis species are dioecious with individuals producing morphologically distinct female or male flowers; whereas, modern domesticated Vitis vinifera cultivars form hermaphrodite flowers capable of self-pollination. Here, we identify the VviPLATZ1 transcription factor as a key candidate female flower morphology factor that localizes to the Vitis SEX-DETERMINING REGION. The expression pattern of this gene correlates with the formation reflex stamens, a prominent morphological phenotype of female flowers. After generating CRISPR/Cas9 gene-edited alleles in a hermaphrodite genotype, phenotype analysis shows that individual homozygous lines produce flowers with reflex stamens. Taken together, our results demonstrate that loss of VviPLATZ1 function is a major factor that controls female flower morphology in Vitis.

Unlike wild Vitis species, which produce either female or male flowers, modern grapevine cultivars form hermaphrodite flowers for self-pollination. Here, the authors report that the VviPLATZ1 (plant AT-rich sequence-and zinc-binding protein1) transcription factor functions in controlling female flower morphology determination.

Regulators of Starch Biosynthesis in Cereal Crops

Starch is the main food source for human beings and livestock all over the world, and it is also the raw material for production of industrial alcohol and biofuel. A considerable part of the world’s annual starch production comes from crops and their seeds. With the increasing demand for starch from food and non-food industries and the growing loss of arable land due to urbanization, understanding starch biosynthesis and its regulators is essential to produce the desirable traits as well as more and better polymers via biotechnological approaches in cereal crops. Because of the complexity and flexibility of carbon allocation in the formation of endosperm starch, cereal crops require a broad range of enzymes and one matching network of regulators to control the providential functioning of these starch biosynthetic enzymes. Here, we comprehensively summarize the current knowledge about regulatory factors of starch biosynthesis in cereal crops, with an emphasis on the transcription factors that directly regulate starch biosynthesis. This review will provide new insights for the manipulation of bioengineering and starch biosynthesis to improve starch yields or qualities in our diets and in industry.

Trihelix Transcription Factor ZmThx20 Is Required for Kernel Development in Maize

Maize kernels are the harvested portion of the plant and are related to the yield and quality of maize. The endosperm of maize is a large storage organ that constitutes 80–90% of the dry weight of mature kernels. Maize kernels have long been the study of cereal grain development to increase yield. In this study, a natural mutation that causes abnormal kernel development, and displays a shrunken kernel phenotype, was identified and named “shrunken 2008 (sh2008)”. The starch grains in sh2008 are loose and have a less proteinaceous matrix surrounding them. The total storage protein and the major storage protein zeins are ~70% of that in the wild-type control (WT); in particular, the 19 kDa and 22 kDa α-zeins. Map-based cloning revealed that sh2008 encodes a GT-2 trihelix transcription factor, ZmThx20. Using CRISPR/Cas9, two other alleles with mutated ZmThx20 were found to have the same abnormal kernel. Shrunken kernels can be rescued by overexpressing normal ZmThx20. Comparative transcriptome analysis of the kernels from sh2008 and WT showed that the GO terms of translation, ribosome, and nutrient reservoir activity were enriched in the down-regulated genes (sh2008/WT). In short, these changes can lead to defects in endosperm development and storage reserve filling in seeds.

Knockdown NRPC2, 3, 8, NRPABC1 and NRPABC2 Affects RNAPIII Activity and Disrupts Seed Development in Arabidopsis

RNA polymerase III (RNAPIII) contains 17 subunits forming 4 functional domains that control the different stages of RNAPIII transcription and are dedicated to the synthesis of small RNAs such as 5S rRNA and tRNAs. Here, we identified 23 genes encoding these subunits in Arabidopsis (Arabidopsis thaliana) and further analyzed 5 subunits (NRPC2, NRPC3, NRPC8, NRPABC1, and NRPABC2) encoded by 6 genes with different expression patterns and belonging to different sub-complexes. The knockdown of these genes repressed the expression of 5S rRNA and tRNAs, causing seed developmental arrest at different stages. Among these knockdown mutants, RNA-seq analysis revealed 821 common differentially expressed genes (DEGs), significantly enriched in response to stress, abscisic acid, cytokinins, and the jasmonic acid signaling pathway. Weighted gene co-expression network analysis (WGCNA) revealed several hub genes involved in embryo development, carbohydrate metabolic and lipid metabolic processes. We identified numerous unique DEGs between the mutants belonging to pathways, including cell proliferation, ribosome biogenesis, cell death, and tRNA metabolic processes. Thus, NRPC2, NRPC3, NRPC8, NRPABC1, and NRPABC2 control seed development in Arabidopsis by influencing RNAPIII activity and, thus, hormone signaling. Reduced expression of these subunit genes causes an insufficient accumulation of the total RNAPIII, leading to the phenotypes observed following the genetic knockdown of these subunits.

Genome-wide analysis of genomic imprinting in the endosperm and allelic variation in flax

Genomic imprinting is an epigenetic phenomenon that causes biased expression of maternally and paternally inherited alleles. In flowering plants, genomic imprinting predominantly occurs in the triploid endosperm and plays a vital role in seed development. In this study, we identified 248 candidate imprinted genes including 114 maternally expressed imprinted genes (MEGs) and 134 paternally expressed imprinted genes (PEGs) in flax (Linum usitatissimum L.) endosperm using deep RNA sequencing. These imprinted genes were neither clustered in specific chromosomal regions nor well conserved among flax and other plant species. MEGs tended to be expressed specifically in the endosperm, whereas the expression of PEGs was not tissue-specific. Imprinted single nucleotide polymorphisms differentiated 200 flax cultivars into the oil flax, oil-fiber dual purpose flax and fiber flax subgroups, suggesting that genomic imprinting contributed to intraspecific variation in flax. The nucleotide diversity of imprinted genes in the oil flax subgroup was significantly higher than that in the fiber flax subgroup, indicating that some imprinted genes underwent positive selection during flax domestication from oil flax to fiber flax. Moreover, imprinted genes that underwent positive selection were related to flax functions. Thirteen imprinted genes related to flax seed size and weight were identified using a candidate gene-based association study. Therefore, our study provides information for further exploration of the function and genomic variation of imprinted genes in the flax population.

Genetic and Molecular Factors Determining Grain Weight in Rice

Grain weight is one of the major factors determining single plant yield production of rice and other cereal crops. Research has begun to reveal the regulatory mechanisms underlying grain weight as well as grain size, highlighting the importance of this research for plant molecular biology. The developmental trait of grain weight is affected by multiple molecular and genetic aspects that lead to dynamic changes in cell division, expansion and differentiation. Additionally, several important biological pathways contribute to grain weight, such as ubiquitination, phytohormones, G-proteins, photosynthesis, epigenetic modifications and microRNAs. Our review integrates early and more recent findings, and provides future perspectives for how a more complete understanding of grain weight can optimize strategies for improving yield production. It is surprising that the acquired wealth of knowledge has not revealed more insights into the underlying molecular mechanisms. To accelerating molecular breeding of rice and other cereals is becoming an emergent and critical task for agronomists. Lastly, we highlighted the importance of leveraging gene editing technologies as well as structural studies for future rice breeding applications.