A conserved HSF:miR169:NF-YA loop involved in tomato and Arabidopsis heat stress tolerance

Heat stress transcription factors (HSFs) and microRNAs (miRNAs) regulate different stress and developmental networks in plants. Regulatory feedback mechanisms are at the basis of these networks. Here, we report that plants improve their heat stress tolerance through HSF-mediated transcriptional regulation of MIR169 and post-transcriptional regulation of Nuclear Factor-YA (NF-YA) transcription factors. We show that HSFs recognize tomato (Solanum lycopersicum) and Arabidopsis MIR169 promoters using yeast one-hybrid/chromatin immunoprecipitation-quantitative PCR. Silencing tomato HSFs using virus-induced gene silencing (VIGS) reduced Sly-MIR169 levels and enhanced Sly-NF-YA9/A10 target expression. Further, Sly-NF-YA9/A10 VIGS knockdown tomato plants and Arabidopsis plants overexpressing At-MIR169d or At-nf-ya2 mutants showed a link with increased heat tolerance. In contrast, Arabidopsis plants overexpressing At-NF-YA2 and those expressing a non-cleavable At-NF-YA2 form (miR169d-resistant At-NF-YA2) as well as plants in which At-miR169d regulation is inhibited (miR169d mimic plants) were more sensitive to heat stress, highlighting NF-YA as a negative regulator of heat tolerance. Furthermore, post-transcriptional cleavage of NF-YA by elevated miR169 levels resulted in alleviation of the repression of the heat stress effector HSFA7 in tomato and Arabidopsis, revealing a retroactive control of HSFs by the miR169:NF-YA node. Hence, a regulatory feedback loop involving HSFs, miR169s and NF-YAs plays a critical role in the regulation of the heat stress response in tomato and Arabidopsis plants.

SP1 and NFY Regulate the Expression of PNPT1, a Gene Encoding a Mitochondrial Protein Involved in Cancer

The Polyribonucleotide nucleotidyltransferase 1 gene (PNPT1) encodes polynucleotide phosphorylase (PNPase), a 3′-5′ exoribonuclease involved in mitochondrial RNA degradation and surveillance and RNA import into the mitochondrion. Here, we have characterized the PNPT1 promoter by in silico analysis, luciferase reporter assays, electrophoretic mobility shift assays (EMSA), chromatin immunoprecipitation (ChIP), siRNA-based mRNA silencing and RT-qPCR. We show that the Specificity protein 1 (SP1) transcription factor and Nuclear transcription factor Y (NFY) bind the PNPT1 promoter, and have a relevant role regulating the promoter activity, PNPT1 expression, and mitochondrial activity. We also found in Kaplan–Meier survival curves that a high expression of either PNPase, SP1 or NFY subunit A (NFYA) is associated with a poor prognosis in liver cancer. In summary, our results show the relevance of SP1 and NFY in PNPT1 expression, and point to SP1/NFY and PNPase as possible targets in anti-cancer therapy.

Genome-Wide Analysis and Expression Profile of Nuclear Factor Y (NF-Y) Gene Family in Z. jujuba

Nuclear factor-Y (NF-Y) is an important transcription factor in the plant species, which potentially provides a higher level of functional diversity including for abiotic stress tolerance. The genome-wide study and expression analysis of NF-Y gene family in Ziziphus, an elite abiotic stress-tolerant species, assist bioprospecting of genes. Here, a total of 32 NF-Y (8 NF-YA, 15 NF-YB, and 9 NF-YC) genes were identified in genome-wide search of Z. jujuba genome. Physicochemical properties, cellular localization, gene structure, chromosomal location, and protein motifs were analyzed for structural and functional understanding. Identified 12 NF-Ys were responsible for the expansion of NF-Y gene family by tandem duplication in Z. jujuba. Phylogenetic and comparative physical mapping of Z. jujuba NF-Ys with its orthologs illustrated evolutionary and functional insights into NF-Y gene family. A total of 45 perfect microsatellites (20bp to 40bp) were extracted across the ZjNF-Y genes. The promoter and gene ontology study suggested that Z. jujuba NF-Y gene family is functionally diverse and could play a wide-ranging role in plant abiotic stress, development, and cellular processes. An expression study revealed that large numbers of the NF-Ys are differentially expressed in response to drought and salinity. The total 15 and 18 ZjNF-Y genes that are upregulated under drought and salinity stress, respectively, are the potential candidates for further functional analysis for development of climate-resilient crops. The present study established a base for understanding the role of NF-Ys in Z. jujuba under abiotic stress conditions and paved a way for further research.

NF-Y subunits overexpression in gastric adenocarcinomas (STAD)

NF-Y is a pioneer transcription factor-TF-formed by the Histone-like NF-YB/NF-YC subunits and the regulatory NF-YA. It binds to the CCAAT box, an element enriched in promoters of genes overexpressed in many types of cancer. NF-YA is present in two major isoforms-NF-YAs and NF-YAl-due to alternative splicing, overexpressed in epithelial tumors. Here we analyzed NF-Y expression in stomach adenocarcinomas (STAD). We completed the partitioning of all TCGA tumor samples (450) according to molecular subtypes proposed by TCGA and ACRG, using the deep learning tool DeepCC. We analyzed differentially expressed genes-DEG-for enriched pathways and TFs binding sites in promoters. CCAAT is the predominant element only in the core group of genes upregulated in all subtypes, with cell-cycle gene signatures. NF-Y subunits are overexpressed, particularly NF-YA. NF-YAs is predominant in CIN, MSI and EBV TCGA subtypes, NF-YAl is higher in GS and in the ACRG EMT subtypes. Moreover, NF-YAlhigh tumors correlate with a discrete Claudinlow cohort. Elevated NF-YB levels are protective in MSS;TP53+ patients, whereas high NF-YAl/NF-YAs ratios correlate with worse prognosis. We conclude that NF-Y isoforms are associated to clinically relevant features of gastric cancer.

TCP7 interacts with Nuclear Factor-Ys to promote flowering by directly regulating SOC1 in Arabidopsis

The success of plant reproduction depends on the timely transition from the vegetative phase to reproductive growth, a process often referred to as flowering. Although several plant-specific transcription factors belonging to the Teosinte Branched 1/Cycloidea/Proliferating Cell Factor (TCP) family are reportedly involved in the regulation of flowering in Arabidopsis, the molecular mechanisms, especially for Class I TCP members, are poorly understood. Here, we genetically identified Class I TCP7 as a positive regulator of flowering time. Protein interaction analysis indicated that TCP7 interacted with several Nuclear Factor-Ys (NF-Ys), known as the 'pioneer' transcription factors; CONSTANS (CO), a main photoperiod regulator of flowering. SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) was differentially expressed in the dominant-negative mutant of TCP7 (lcu) and the loss-of-function mutant of Class I TCP members (septuple). Additionally, we obtained genetic and molecular evidence showing that TCP7 directly activates the flowering integrator gene, SOC1. Moreover, TCP7 synergistically activated SOC1 expression upon interacting with CO and NF-Ys in vivo. Collectively, our results provide compelling evidence that TCP7 synergistically interacts with NF-Ys to activate the transcriptional expression of the flowering integrator gene SOC1.

The CCAAT-binding complex mediates azole susceptibility of Aspergillus fumigatus by suppressing SrbA expression and cleavage

In fungal pathogens, the transcription factor SrbA (a sterol regulatory element-binding protein, SREBP) and CBC (CCAAT binding complex) have been reported to regulate azole resistance by competitively binding the TR34 region (34 mer) in the promoter of the drug target gene, erg11A. However, current knowledge about how the SrbA and CBC coordinately mediate erg11A expression remains limited. In this study, we uncovered a novel relationship between HapB (a subunit of CBC) and SrbA in which deletion of hapB significantly prolongs the nuclear retention of SrbA by increasing its expression and cleavage under azole treatment conditions, thereby enhancing Erg11A expression for drug resistance. Furthermore, we verified that loss of HapB significantly induces the expression of the rhomboid protease RbdB, Dsc ubiquitin E3 ligase complex, and signal peptide peptidase SppA, which are required for the cleavage of SrbA, suggesting that HapB acts as a repressor for these genes which contribute to the activation of SrbA by proteolytic cleavage. Together, our study reveals that CBC functions not only to compete with SrbA for binding to erg11A promoter region but also to affect SrbA expression, cleavage, and translocation to nuclei for the function, which ultimately regulate Erg11A expression and azole resistance.

Nuclear Factor-Y in Mouse Pancreatic β-Cells Plays a Crucial Role in Glucose Homeostasis by Regulating β-Cell Mass and Insulin Secretion

Pancreatic β-cell mass and insulin secretion are determined by the dynamic change of transcription factor expression levels in response to altered metabolic demand. Nuclear factor-Y (NF-Y) is an evolutionarily conserved transcription factor playing critical roles in multiple cellular processes. However, the physiological role of NF-Y in pancreatic β-cells is poorly understood. The current study was undertaken in a conditional knockout of Nf-ya specifically in pancreatic β-cells (Nf-ya βKO) to define the essential physiological role of NF-Y in β-cells. Nf-ya βKO mice exhibited glucose intolerance without changes in insulin sensitivity. Reduced β-cell proliferation resulting in decreased β-cell mass was observed in these mice, which was associated with disturbed actin cytoskeleton. NF-Y-deficient β-cells also exhibited impaired insulin secretion with a reduced Ca²⁺ influx in response to glucose, which was associated with an inefficient glucose uptake into β-cells due to a decreased expression of GLUT2 and a reduction in ATP production resulting from the disruption of mitochondrial integrity. This study is the first to show that NF-Y is critical for pancreatic islet homeostasis and function through regulation in β-cell proliferation, glucose uptake into β-cells, and mitochondrial energy metabolism. Modulating NF-Y expression in β-cells may therefore offer an attractive approach for therapeutic intervention.

The rice LEC1-like transcription factor OsNF-YB9 interacts with SPK, an endosperm-specific sucrose synthase protein kinase, and functions in seed development

LEAFY COTYLEDON1 (LEC1), a NUCLEAR FACTOR-Y (NF-Y) family member, plays a critical role in embryogenesis and seed development in Arabidopsis. Previous studies have shown that rice OsNF-YB9 and OsNF-YB7 are homologous to Arabidopsis LEC1. However, the functions of LEC1-like genes in rice remain unclear. Here we report that OsNF-YB9 and OsNF-YB7 display sub-functionalization in rice. We demonstrate that OsNF-YB7 is expressed mainly in the embryo, whereas OsNF-YB9 is preferentially expressed in the developing endosperm. Heterologous expression of either OsNF-YB9 or OsNF-YB7 in Arabidopsis lec1-1 was able to complement the lec1-1 defects. We failed to generate osnf-yb7 homozygous mutants due to lethality caused by OsNF-YB7 defects. Loss of OsNF-YB9 function caused abnormal seed development: seeds were longer, narrower and thinner and exhibited a higher chalkiness ratio. Furthermore, the expression of genes related to starch synthesis was deregulated in osnf-yb9. OsNF-YB9 could interact with SPK, a sucrose synthase protein kinase that is predominantly expressed in rice endosperm. Knockout of SPK resulted in chalky seeds similar to those observed in the osnf-yb9 mutants. Ectopic expression of OsNF-YB9 in both rice and Arabidopsis resulted in unhealthy plants with small seeds. Taken together, these results suggest a critical role for OsNF-YB9 in rice seed development.

Live cell dynamics of the NF-Y transcription factor

Transcription factors (TFs) are core players in the control of gene expression, evolutionarily selected to recognise a subset of specific DNA sequences and nucleate the recruitment of the transcriptional machinery. How TFs assemble and move in the nucleus to locate and bind their DNA targets and cause a transcriptional response, remains mostly unclear. NF-Y is a highly conserved, heterotrimeric TF with important roles in both housekeeping and lineage-specific gene expression, functioning as a promoter organiser. Despite a large number of biochemical, structural and genomic studies of NF-Y, there is a lack of experiments in single living cells; therefore, basic assumptions of NF-Y biology remain unproven in vivo. Here we employ a series of dynamic fluorescence microscopy methods (FLIM-FRET, NB, RICS and FRAP) to study NF-Y dynamics and complex formation in live cells. Specifically, we provide quantitative measurement of NF-Y subunit association and diffusion kinetics in the nucleus that collectively suggest NF-Y to move and bind chromatin as a trimeric complex in vivo.

Integrating quantitative proteomics with accurate genome profiling of transcription factors by greenCUT&RUN

Genome-wide localization of chromatin and transcription regulators can be detected by a variety of techniques. Here, we describe a novel method 'greenCUT&RUN' for genome-wide profiling of transcription regulators, which has a very high sensitivity, resolution, accuracy and reproducibility, whilst assuring specificity. Our strategy begins with tagging of the protein of interest with GFP and utilizes a GFP-specific nanobody fused to MNase to profile genome-wide binding events. By using a GFP-nanobody the greenCUT&RUN approach eliminates antibody dependency and variability. Robust genomic profiles were obtained with greenCUT&RUN, which are accurate and unbiased towards open chromatin. By integrating greenCUT&RUN with nanobody-based affinity purification mass spectrometry, 'piggy-back' DNA binding events can be identified on a genomic scale. The unique design of greenCUT&RUN grants target protein flexibility and yields high resolution footprints. In addition, greenCUT&RUN allows rapid profiling of mutants of chromatin and transcription proteins. In conclusion, greenCUT&RUN is a widely applicable and versatile genome-mapping technique.

KLF5 and NFYA factors as novel regulators of prostate cancer cell metabolism

Prostate cancer (PCa) cells rely on the androgen receptor (AR) signaling axis to reprogram metabolism to sustain aberrant proliferation. Whether additional transcription factors participate to this reprogramming remains mostly unknown. To identify such factors, DNA motif analyses were performed in the promoter and regulatory regions of genes sensitive to androgens in PCa cells. These analyses identified two transcription factors, KLF5 and NFYA, as possibly associated with PCa cell metabolism. In clinical datasets, KLF5 and NFYA expression levels were associated with disease aggressiveness, being significantly decreased and increased, respectively, during PCa progression. Their expression was next investigated by qPCR and Western blot in human PCa cell models, revealing a positive regulation of KLF5 by androgens and a correlation between NFYA and AR protein expression status. siRNA-mediated knockdown of KLF5 increased human PCa cell proliferation rate in AR-positive cell models, suggesting a tumor suppressor function. Live-cell metabolic assays showed that knockdown of KLF5 promoted mitochondrial respiration, a key metabolic pathway associated with PCa progression. The opposite was observed for knockdown of NFYA regarding proliferation and respiration. RNA-seq analyses following the knockdown of either KLF5 and NFYA confirmed that both factors regulated distinct metabolic gene signatures, as well as other gene signatures, explaining their differential impact on PCa cell proliferation and metabolism. Overall, our findings identify KLF5 and NFYA as novel regulators of PCa cell metabolism.

Transcription factor competition at the γ-globin promoters controls hemoglobin switching

BCL11A, the major regulator of fetal hemoglobin (HbF, α2γ2) level, represses γ-globin expression through direct promoter binding in adult erythroid cells in a switch to adult hemoglobin (HbA, α2β2). To uncover how BCL11A initiates repression, we used CRISPR-Cas9, dCas9, dCas9-KRAB and dCas9-VP64 screens to dissect the γ-globin promoters and identified an activator element near the BCL11A-binding site. Using CUT&RUN and base editing, we demonstrate that a proximal CCAAT box is occupied by the activator NF-Y. BCL11A competes with NF-Y binding through steric hindrance to initiate repression. Occupancy of NF-Y is rapidly established following BCL11A depletion, and precedes γ-globin derepression and locus control region (LCR)-globin loop formation. Our findings reveal that the switch from fetal to adult globin gene expression within the >50-kb β-globin gene cluster is initiated by competition between a stage-selective repressor and a ubiquitous activating factor within a remarkably discrete region of the γ-globin promoters.

GmNF-YC4-2 Increases Protein, Exhibits Broad Disease Resistance and Expedites Maturity in Soybean

The NF-Y gene family is a highly conserved set of transcription factors. The functional transcription factor complex is made up of a trimer between NF-YA, NF-YB, and NF-YC proteins. While mammals typically have one gene for each subunit, plants often have multigene families for each subunit which contributes to a wide variety of combinations and functions. Soybean plants with an overexpression of a particular NF-YC isoform GmNF-YC4-2 (Glyma.04g196200) in soybean cultivar Williams 82, had a lower amount of starch in its leaves, a higher amount of protein in its seeds, and increased broad disease resistance for bacterial, viral, and fungal infections in the field, similar to the effects of overexpression of its isoform GmNF-YC4-1 (Glyma.06g169600). Interestingly, GmNF-YC4-2-OE (overexpression) plants also filled pods and senesced earlier, a novel trait not found in GmNF-YC4-1-OE plants. No yield difference was observed in GmNF-YC4-2-OE compared with the wild-type control. Sequence alignment of GmNF-YC4-2, GmNF-YC4-1 and AtNF-YC1 indicated that faster maturation may be a result of minor sequence differences in the terminal ends of the protein compared to the closely related isoforms.

Cloning and functional characterization of seed-specific LEC1A promoter from peanut (Arachis hypogaea L.)

LEAFY COTYLEDON1 (LEC1) is a HAP3 subunit of CCAAT-binding transcription factor, which controls several aspects of embryo and postembryo development, including embryo morphogenesis, storage reserve accumulation and skotomorphogenesis. Herein, using the method of chromosomal walking, a 2707bp upstream sequence from the ATG initiation codon site of AhLEC1A which is a homolog of Arabidopsis LEC1 was isolated in peanut. Its transcriptional start site confirmed by 5’ RACE was located at 82 nt from 5’ upstream of ATG. The bioinformatics analysis revealed that there existed many tissue-specific elements and light responsive motifs in its promoter. To identify the functional region of the AhLEC1A promoter, seven plant expression vectors expressing the GUS (β-glucuronidase) gene, driven by 5’ terminal series deleted fragments of AhLEC1A promoter, were constructed and transformed into Arabidopsis. Results of GUS histochemical staining showed that the regulatory region containing 82bp of 5’ UTR and 2228bp promoter could facilitate GUS to express preferentially in the embryos at different development periods of Arabidopsis. Taken together, it was inferred that the expression of AhLEC1A during seed development of peanut might be controlled positively by several seed-specific regulatory elements, as well as negatively by some other regulatory elements inhibiting its expression in other organs. Moreover, the GUS expression pattern of transgenic seedlings in darkness and in light was relevant to the light-responsive elements scattered in AhLEC1A promoter segment, implying that these light-responsive elements harbored in the AhLEC1A promoter regulate skotomorphogenesis of peanut seeds, and AhLEC1A expression was inhibited after the germinated seedlings were transferred from darkness to light.

DeepSRE: Identification of sterol responsive elements and nuclear transcription factors Y proximity in human DNA by Convolutional Neural Network analysis

SREBP1 and 2, are cholesterol sensors able to modulate cholesterol-related gene expression responses. SREBPs binding sites are characterized by the presence of multiple target sequences as SRE, NFY and SP1, that can be arranged differently in different genes, so that it is not easy to identify the binding site on the basis of direct DNA sequence analysis. This paper presents a complete workflow based on a one-dimensional Convolutional Neural Network (CNN) model able to detect putative SREBPs binding sites irrespective of target elements arrangements. The strategy is based on the recognition of SRE linked (less than 250 bp) to NFY sequences according to chromosomal localization derived from TF Immunoprecipitation (TF ChIP) experiments. The CNN is trained with several 100 bp sequences containing both SRE and NF-Y. Once trained, the model is used to predict the presence of SRE-NFY in the first 500 bp of all the known gene promoters. Finally, genes are grouped according to biological process and the processes enriched in genes containing SRE-NFY in their promoters are analyzed in details. This workflow allowed to identify biological processes enriched in SRE containing genes not directly linked to cholesterol metabolism and possible novel DNA patterns able to fill in for missing classical SRE sequences.

NF-Y plays essential roles in flavonoid biosynthesis by modulating histone modifications in tomato

NF-Y transcription factors are reported to play diverse roles in a wide range of biological processes in plants. However, only a few active NF-Y complexes are known in plants and the precise functions of NF-Y complexes in flavonoid biosynthesis have not been determined. Using various molecular, genetic and biochemical approaches, we found that NF-YB8a, NF-YB8b and NF-YB8c - a NF-YB subgroup - can interact with a specific subgroup of NF-YC and then recruit either of two distinct NF-YAs to form NF-Y complexes that bind the CCAAT element in the CHS1 promoter. Furthermore, suppressing the expression of particular NF-YB genes increased the levels of H3K27me3 at the CHS1 locus and significantly suppressed the expression of CHS1 during tomato fruit ripening, which led to the development of pink-coloured fruit with colourless peels. Altogether, by demonstrating that NF-Y transcription factors play essential roles in flavonoid biosynthesis and by providing significant molecular insight into the regulatory mechanisms that drive the development of pink-coloured tomato fruit, we provide a major advance to our fundamental knowledge and information that has considerable practical value for horticulture.

The soybean GmNFY-B1 transcription factor positively regulates flowering in transgenic Arabidopsis

Nuclear Factor Y (NF-Y) gene family regulates numbers of flowering processes. Two independent transgenic Arabidopsis lines overexpressing (OX) GmNFY-B1 and GmNFYB1-GR (GmNFYB1 fused with the glucocorticoid receptor) were used to investigate the function of NFY-B1 in flowering. Furthermore, GmNFYB1-GR lines were chemically treated with dexamethasone (Dex, synthetic steroid hormone), cycloheximide (Cyc, an inhibitor of protein biosynthesis), and ethanol to examine their effects on different flowering related marker genes. Our results indicated that the transgenic lines produced longer hypocotyl lengths and had fewer numbers of rosette leaves compared to the wild-type and nf-yb1 mutant plants under both long and short-day (LD and SD) conditions. The qRT-PCR assays revealed that transcript levels of all flowering time regulating genes, i.e. SOC, FLC, FT, TSF, LFY, GI2, AGL, and FCA showed higher transcript abundance in lines OX GmNFYB1-GR. However, FT and GI genes showed higher transcript levels under Dex and Dex/Cyc treatments compared to Cyc and ethanol. Additionally, 24 differentially expressed genes were identified and verified through RNA-seq and RT-qPCR in GmNF-YB1-GR lines under Cyc and Dex/Cyc treatments from which 14 genes were up-regulated and 10 were down-regulated. These genes are involved in regulatory functions of circadian rhythm, regulation of flower development in photoperiodic, and GA pathways. The overexpression of GmNF-YB1 and GmNF-YB1-GR promote flowering through the higher expression of flowering-related genes. Further GmNF-YB1 and its attachment with the GR receptor can regulate its target genes under Dex/Cyc treatment and might act as flowering inducer under LD and SD conditions.

Transcriptome-wide isolation and expression of NF-Y gene family in male cone development and hormonal treatment of Pinus tabuliformis

It is known that nuclear factor Y (NF-Y) transcription factors play an important role in flowering time regulation and hormone response (ABA, GA) in angiosperms, but, little known in conifers. Moreover, the NF-Y gene family has not been comprehensively reported in conifers. Here, we identified 9 NF-YA, 9 NF-YB and 10 NF-YC genes in Pinus tabuliformis using Arabidopsis NF-Y protein sequences as queries. Additionally, by comparing conserved regions and phylogenetic relationships of the PtNF-Ys, we found that NF-Ys were both conserved and altered during evolution. PtTFL2, PtCO, PtNF-YC1 and PtNF-YC4 were exploited by expression profile in male cone development and correlation analysis. Furthermore, NF-YC1/4 and DPL (DELLA protein of P. tabuliformis) were interacted by yeast two-hybrid and BiFC assays, which suggested that NF-YC1/4 may be involved in gibberellins signaling pathway. Moreover, the multiple types of phytohormones-responsive cis-elements (ABA, JA, IAA, SA) have been found, and gene expression profile analysis showed that many NF-Y genes responded positively to SA and as opposed to IAA and JA, revealing the potential role of NF-Ys in conifers resistance. In summary, this study provided the basis for further investigation of the function of NF-Y genes in conifers.

miR169 and PmRGL2 synergistically regulate the NF-Y complex to activate dormancy release in Japanese apricot (Prunus mume Sieb. et Zucc.)

This study is the first to demonstrate that GA₄-induced dormancy release is associated with the NF-Y complex, which interacts with gibberellin inhibitor RGL2 in Japanese apricot. Seasonal dormancy is not only vital for the survival in cold winter but also affects flowering of temperate fruit trees and the dormancy release depends on the accumulation of the cold temperatures (Chilling requirement-CR). To understand the mechanism of dormancy release in deciduous fruit crops, we compared miRNA sequencing data during the transition stage from paradormancy to dormancy release in the Japanese apricot and found that the miR169 family showed significant differentially up-regulated expression during dormancy induction and was down-regulated during the dormancy release periods. The 5' RACE assay and RT-qPCR validated its target gene NUCLEAR FACTOR-Y subunit A (NF-YA), which exhibited the opposite expression pattern. Further study showed that exogenous GA₄ could inhibit the expression of the gibberellic acid (GA) signal transduction suppressor PmRGL2 (RGA-LIKE 2) and promote the expression of NF-Y. Moreover, the interaction between the NF-Y family and GA inhibitor PmRGL2 was verified by the yeast-two-hybrid (Y2H) system and a bimolecular fluorescence complementarity (BiFC) experiment. These results suggest that synergistic regulation of the NF-Y and PmRGL2 complex leads to the activation of dormancy release induced by GA₄. These findings will help to elucidate the functional and regulatory roles of miR169 and NF-Y complex in seasonal bud dormancy induced by GA in Japanese apricot and provide new insights for the discovery of dormancy release mechanisms in woody plants.

Structural determinants for NF-Y subunit organization and NF-Y/DNA association in plants

NF-Y transcription factor comprises three subunits: NF-YA, NF-YB and NF-YC. NF-YB and NF-YC dimerize through their histone fold domain (HFD), which can bind DNA in a non-sequence-specific fashion while serving as a scaffold for NF-YA trimerization. Upon trimerization, NF-YA specifically recognizes the CCAAT box sequence on promoters and enhancers. In plants, each NF-Y subunit is encoded by several genes giving rise to hundreds of potential heterotrimeric combinations. In addition, plant NF-YBs and NF-YCs interact with other protein partners to recognize a plethora of genomic motifs, as the CCT protein family that binds CORE sites. The NF-Y subunit organization and its DNA-binding properties, together with the NF-Y HFD capacity to adapt different protein modules, represent plant-specific features that play a key role in development, growth and reproduction. Despite their relevance, these features are still poorly understood at the molecular level. Here, we present the structures of Arabidopsis and rice NF-YB/NF-YC dimers, and of an Arabidopsis NF-Y trimer in complex with the FT CCAAT box, together with biochemical data on NF-Y mutants. The dimeric structures identify the key residues for NF-Y HFD stabilization. The NF-Y/DNA structure and the mutation experiments shed light on HFD trimerization interface properties and the NF-YA sequence appetite for the bases flanking the CCAAT motif. These data explain the logic of plant NF-Y gene expansion: the trimerization adaptability and the flexible DNA-binding rules serve the scopes of accommodating the large number of NF-YAs, CCTs and possibly other NF-Y HFD binding partners and a diverse audience of genomic motifs.

Functional and transcriptomic analyses of the NF-Y family provide insights into the defense mechanisms of honeybees under adverse circumstances

As predominant pollinators, honeybees are important for crop production and terrestrial ecosystems. Recently, various environmental stresses have led to large declines in honeybee populations in many regions. The ability of honeybees to respond to these stresses is critical for their survival. However, the details of the stress defense mechanisms of honeybees have remained elusive. Here, we found that the Nuclear Factor Y (NF-Y) family (containing NF-YA, NF-YB, and NF-YC) is a novel stress mediator family that regulates honeybee environmental stress resistance. NF-YA localized in the nucleus, NF-YB accumulated in the cytoplasm, and NF-YC presented in both the nucleus and cytoplasm. NF-YC interacted with NF-YA and NF-YB in vitro and in vivo, and the nuclear import of NF-YB relied on its interaction with NF-YC. We further found that the expression of NF-Y was induced under multiple stress conditions. In addition, NF-Y regulated many stress responses and antioxidant genes at the transcriptome-wide level, and knockdown of NF-Y repressed the expression of stress-inducible genes, particularly LOC108003540 and LOC107994062, under adverse circumstances. Silencing NF-Y lowered honeybee stress resistance by reducing total antioxidant capacity and enhancing oxidative impairment. Collectively, these results indicate that NF-Y plays important roles in stress responses. Our study sheds light on the underlying defense mechanisms of honeybees under environmental stress.

OsbZIP76 interacts with OsNF-YBs and regulates endosperm cellularization in rice (Oryza sativa)

Following double fertilization, plant endosperm nuclei undergo syncytial divisions, followed by synchronous cellularization. Cellularization is a key event during endosperm development, but our understanding of its regulation is limited to Arabidopsis. In this study we show that OsbZIP76 regulates cellularization in rice (Oryza sativa). Activation of OsbZIP76 coincided with the initiation of cellularization, and its knockdown or knockout mutants exhibited precocious cellularization. Genes involved in endosperm development or starch biosynthesis were prematurely activated in the osbzip76 caryopsis. As a putative transcription factor, OsbZIP76 alone lacked transcriptional activation activity; however, it interacted with the nuclear factor Y (NF-Y) family transcription factors OsNF-YB9 and OsNF-YB1 in yeast and in planta. OsbZIP76 and OsNF-YB9 were predominantly expressed in the endosperm and the proteins colocalized. Seeds of osnf-yb1 and osbzip76 mutants showed reduced size and reduced apparent amylose content. The parent-of-origin-dependent expression of OsbZIP76 is variable in different rice accessions. In summary, OsbZIP76 is an endosperm-expressed imprinted gene that regulates endosperm development in rice.

NF-Y Overexpression in Liver Hepatocellular Carcinoma (HCC)

NF-Y is a pioneer trimeric transcription factor formed by the Histone Fold Domain (HFD) NF-YB/NF-YC subunits and NF-YA. Three subunits are required for DNA binding. CCAAT-specificity resides in NF-YA and transactivation resides in Q-rich domains of NF-YA and NF-YC. They are involved in alternative splicing (AS). We recently showed that NF-YA is overexpressed in breast and lung carcinomas. We report here on the overexpression of all subunits in the liver hepatocellular carcinoma (HCC) TCGA database, specifically the short NF-YAs and NF-YC2 (37 kDa) isoforms. This is observed at all tumor stages, in viral-infected samples and independently from the inflammatory status. Up-regulation of NF-YAs and NF-YC, but not NF-YB, is associated to tumors with mutant p53. We used a deep-learning-based method (DeepCC) to extend the partitioning of the three molecular clusters to all HCC TCGA tumors. In iCluster3, CCAAT is a primary matrix found in promoters of up-regulated genes, and cell-cycle pathways are enriched. Finally, clinical data indicate that, globally, only NF-YAs, but not HFD subunits, correlate with the worst prognosis; in iCluster1 patients, however, all subunits correlate. The data show a difference with other epithelial cancers, in that global overexpression of the three subunits is reported and clinically relevant in a subset of patients; yet, they further reinstate the regulatory role of the sequence-specific subunit.

Aux/IAA14 Regulates microRNA-Mediated Cold Stress Response in Arabidopsis Roots

The phytohormone auxin and microRNA-mediated regulation of gene expressions are key regulators of plant growth and development at both optimal and under low-temperature stress conditions. However, the mechanistic link between microRNA and auxin in regulating plant cold stress response remains elusive. To better understand the role of microRNA (miR) in the crosstalk between auxin and cold stress responses, we took advantage of the mutants of Arabidopsis thaliana with altered response to auxin transport and signal. Screening of the mutants for root growth recovery after cold stress at 4 °C revealed that the auxin signaling mutant, solitary root 1 (slr1; mutation in Aux/IAA14), shows a hypersensitive response to cold stress. Genome-wide expression analysis of miRs in the wild-type and slr1 mutant roots using next-generation sequencing revealed 180 known and 71 novel cold-responsive microRNAs. Cold stress also increased the abundance of 26-31 nt small RNA population in slr1 compared with wild type. Comparative analysis of microRNA expression shows significant differential expression of 13 known and 7 novel miRs in slr1 at 4 °C compared with wild type. Target gene expression analysis of the members from one potential candidate miR, miR169, revealed the possible involvement of miR169/NF-YA module in the Aux/IAA14-mediated cold stress response. Taken together, these results indicate that SLR/IAA14, a transcriptional repressor of auxin signaling, plays a crucial role in integrating miRs in auxin and cold responses.

Overexpression of GmNFYA5 confers drought tolerance to transgenic Arabidopsis and soybean plants

BACKGROUND

Crop productivity is challenged by abiotic stresses, among which drought stress is the most common. NF-Y genes, especially NF-YA genes, regulate tolerance to abiotic stress.

RESULTS

Soybean NF-Y gene GmNFYA5 was identified to have the highest transcript level among all 21 NF-YA genes in soybean (Glycine max L.) under drought stress. Drought-induced transcript of GmNFYA5 was suppressed by the ABA synthesis inhibitor naproxen (NAP). GmNFYA5 transcript was detected in various tissues at vegetative and reproductive growth stages with higher levels in roots and leaves than in other tissues, which was consist with the GmNFYA5 promoter: GUS fusion assay. Overexpression of GmNFYA5 in transgenic Arabidopsis plants caused enhanced drought tolerance in seedlings by decreasing stomatal aperture and water loss from leaves. Overexpression and suppression of GmNFYA5 in soybean resulted in increased and decreased drought tolerance, respectively, relative to plants with an empty vector (EV). Transcript levels of ABA-dependent genes (ABI2, ABI3, NCED3, LEA3, RD29A, P5CS1, GmWRKY46, GmNCED2 and GmbZIP1) and ABA-independent genes (DREB1A, DREB2A, DREB2B, GmDREB1, GmDREB2 and GmDREB3) in transgenic plants overexpressing GmNFYA5 were higher than those of wild-type plants under drought stress; suppression of GmNFYA5 transcript produced opposite results. GmNFYA5 probably regulated the transcript abundance of GmDREB2 and GmbZIP1 by binding to the promoters in vivo.

CONCLUSIONS

Our results suggested that overexpression of GmNFYA5 improved drought tolerance in soybean via both ABA-dependent and ABA-independent pathways.