Transcriptional regulation of secretory capacity by bZip transcription factors

Cells of specialized secretory organs expand their secretory pathways to accommodate the increased protein load necessary for their function. The endoplasmic reticulum （ER）, the Golgi apparatus and the secretory vesicles, expand not only the membrane components but also the protein machinery required for increased protein production and transport. Increased protein load causes an ER stress response akin to the Unfolded Protein Response （UPR）. Recent work has implicated several bZip transcription factors in the regulation of protein components of the early secretory pathway necessary to alleviate this stress. Here, we highlight eight bZip transcription factors in regulating secretory pathway component genes. These include components of the three canonical branches of the UPR-ATF4, XBP1, and ATF6, as well as the five members of the Creb3 family of transcription factors. We review findings from both invertebrate and vertebrate model systems suggesting that all of these proteins increase secretory capacity in response to increased protein load. Finally, we propose that the Creb3 family of factors may have a dual role in secretory cell differentiation by also regulating the pathways necessary for cell cycle exit during terminal differentiation.

Identifi cation and characterization of the bZIP transcription factor family in yellowhorn

The basic leucine zipper(bZIP)transcription factor family is one of the largest and most diverse families in plants,regulating plant growth and development and playing an essential role in response to abiotic and biotic stresses.However,little is known about the biological functions of bZIP proteins in yellowhorn(Xanthoceras sorbifolium).Recently,64 XsbZIP genes were identifi ed in the yellowhorn genome and found to be disproportionately distributed in linkage groups.The XsbZIP proteins clustered into 11 groups based on their phylogenetic relationships with AtbZIP,ZmbZIP and GmbZIP proteins.Five intron patterns in the basic and hinge regions and additional conserved motifs were defi ned,both supporting the group classifi cation and possibly contributing to their functional diversity.Compared to tandem duplication,the segment duplication greatly contributed to the expansion of yellowhorn bZIP genes.In addition,most XsbZIP genes harbor several stress responsive cis-elements in their promoter regions.Moreover,the RNA-seq and qRT-PCR data indicated XsbZIP genes were extensively involved in response to various stresses,including salt(NaCl),cold and abscisic acid,with possibly diff erent molecular mechanisms.These results provide a new understanding of the biological functions of bZIP transcription factors in yellowhorn.

Genome-wide investigation of the bZIP transcription factor gene family in Prunus mume:Classification, evolution, expression profile and low-temperature stress responses

Prunus mume is an important woody plant that has high ornamental and economic value, widely distributed and used in landscape architecture in East Asia. In plants, basic(region) leucine zipper(bZIP) transcription factors play important regulatory roles in growth, development,dormancy and abiotic stress. To date, bZIP transcription factors have not been systematically studied in P. mume. In this study, 49 bZIP genes were first identified in P. mume, and the PmbZIP family was divided into 12 groups according to the grouping principles for the Arabidopsis thaliana bZIP family. For the first time, we constructed a detailed model of the PmbZIP domains(R-x_(3)–N-(x)_7-R/K-x_(2)-K-x_(6)-L-x_(6)-L-_(6)-L). Phylogenetic and synteny analyses showed that PmbZIPs duplication events might have occurred during the large-scale genome duplication events. A relatively short time of speciation and the finding that 91.84% of the bZIP genes formed orthologous pairs between P. mume and Prunus armeniaca provided evidence of a close relationship. Gene expression patterns were analysed in different tissues and periods, indicating that PmbZIP genes with the same motifs exhibited similar expression patterns. The gene expression results showed that PmbZIP31/36/41 genes played a more prominent role in the response to freezing stress than cold stress. The expression level of almost all subset Ⅲ genes was upregulated under freezing treatment, especially after cold exposure. We analysed the gene expression patterns of PmbZIP12/31/36/41/48 and their responses to low-temperature stress, which provided useful resources for future studies on the cold/freezing-tolerant molecular breeding of P. mume.

The ferroptosis activity is associated with neurological recovery following chronic compressive spinal cord injury

Chronic compressive spinal cord injury in compressive cervical myelopathy conditions can lead to rapid neurological deterioration in the early phase,followed by partial self-recovery,and ultimately an equilibrium state of neurological dysfunction.Ferroptosis is a crucial pathological process in many neurodegenerative diseases;however,its role in chro nic compressive spinal cord injury remains unclear.In this study,we established a chronic compressive spinal cord injury rat model,which displayed its most severe behavioral and electrophysiological dysfunction at 4 wee ks and partial recovery at 8 weeks after compression.Bulk RNA sequencing data identified enriched functional pathways,including ferroptosis,presynapse,and postsynaptic membrane activity at both 4 and 8 wee ks following chro nic compressive spinal co rd injury.Tra nsmission electron microscopy and malondialdehyde quantification assay confirmed that ferroptosis activity peaked at 4 weeks and was attenuated at 8 weeks after chronic compression.Ferro ptosis activity was negatively correlated with behavioral score.Immunofluorescence,quantitative polymerase chain reaction,and western blotting showed that expression of the anti-ferroptosis molecules,glutathione peroxidase 4(GPX4) and MAF BZIP transcription factor G(MafG),in neuro ns was suppressed at 4 weeks and upregulated at 8 weeks following spinal co rd compression.There was a positive correlation between the expression of these two molecules,suggesting that they may work together to contribute to functional recovery following chronic compressive spinal cord injury.In conclusion,our study determined the genome-wide expression profile and fe rroptosis activity of a consistently compressed spinal cord at different time points.The results showed that anti-fe rroptosis genes,specifically GPX4 and MafG,may be involved in spontaneous neurological recovery at 8 weeks of chronic compressive spinal cord injury.These findings contribute to a better understanding of the mechanisms underlying chronic compressive spinal cord injury and may help identify new therapeutic targets for compressive cervical myelopathy.

The bZIP transcription factor ATF1 regulates blue light and oxidative stress responses in Trichoderma guizhouense

In several filamentous fungi,incident light and environmental stress signaling share the mitogen-activated protein kinase(MAPK)HOG(SAK)pathway.It has been revealed that short-term illumination with blue light triggers the activation of the HOG pathway in Trichoderma spp.In this study,we demonstrate the crucial role of the basic leucine zipper transcription factor ATF1 in blue light responses and signaling downstream of the MAPK HOG1 in Trichoderma guizhouense.The lack of ATF1 severely impaired photoconidiation and delayed vegetative growth and conidial germination.Upon blue light or H2O2 stimuli,HOG1 interacted with ATF1 in the nucleus.Genome-wide transcriptome analyses revealed that 61.8%(509 out of 824)and 85.2%(702 out of 824)of blue light-regulated genes depended on ATF1 and HOG1,respectively,of which 58.4%(481 out of 824)were regulated by both of them.Our results also show that blue light promoted conidial germination and HOG1 and ATF1 played opposite roles in controlling conidial germination in the dark.Additionally,the lack of ATF1 led to reduced oxidative stress resistance,probably because of the downregulation of catalase-encoding genes.Overall,our results demonstrate that ATF1 is the downstream component of HOG1 and is responsible for blue light responses,conidial germination,vegetative growth,and oxidative stress resistance in T.guizhouense.

The Arabidopsis bZIP1 Transcription Factor Is Involved in Sugar Signaling, Protein Networking, and DNA Binding

Sugar signaling is a mechanism that plants use to integrate various internal and external cues to achieve nutrient homeostasis, mediate developmental programs, and articulate stress responses. Many bZlP transcription factors are known to be involved in nutrient and/or stress signaling. An Arabidopsis Sl-group bZlP gene, AtbZIP1, was identified as a sugar-sensitive gene in a previous gene expression profiling study （Plant Cell. 16, 2128-2150）. In this report, we show that the expression of AtbZIP1 is repressed by sugars in a fast, sensitive, and reversible way. The sugar repression of Atb- ZIP1 is affected by a conserved sugar signaling component, hexokinase. Besides being a sugar-regulated gene, AtbZIP1 can mediate sugar signaling and affect gene expression, plant growth, and development. When carbon nutrients are limited, gain or loss of function of AtbZlP1 causes changes in the rates of early seedling establishment. Results of phenotypic analyses indicate that AtbZlP1 acts as a negative regulator of early seedling growth. Using gain- and loss-of-function plants in a microarray analysis, two sets of putative AtbZIP1-regulated genes have been identified. Among them, sugar-responsive genes are highly over-represented, implicating a role of AtbZlP1 in sugar-mediated gene expression. Using yeast two-hybrid （Y-2-H） screens and bimolecular fluorescence complementation （BiFC） analyses, we are able to recapitulate extensive C/S1 AtbZlP protein interacting network in living cells. Finally, we show that AtbZIP1 can bind ACGT-based motifs in vitro and that the binding characteristics appear to be affected by the heterodimerization between AtbZlP1 and the C-group AtbZIPs, including AtbZlP10 and AtbZlP63.

The transcription factor HBF1 directly activates expression of multiple flowering time repressors to delay rice flowering

Flowering time(or heading date)is an important agronomic trait that determines the environmental adaptability and yield of many crops,including rice(Oryza sativa L.).Hd3a BINDING REPRESSOR FACTOR 1(HBF1),a basic leucine zipper transcription factor,delays flowering by decreasing the expression of Early heading date 1(Ehd1),Heading date 3a(Hd3a),and RICE FLOWERING LOCUS T 1(RFT1),but the underlying molecular mechanisms have not been fully elucidated.Here,we employed the hybrid transcriptional factor(HTF)strategy to enhance the transcriptional activity of HBF1 by fusing it to four copies of the activation domain from Herpes simplex virus VP16.We discovered that transgenic rice lines overexpressing HBF1-VP64(HBF1V)show significant delays in time to flower,compared to lines overexpressing HBF1-MYC or wild-type plants,via the Ehd1–Hd3a/RFT1 pathway,under both long-day and short-day conditions.Transcriptome deep sequencing analysis indicated that 19 WRKY family genes are upregulated in the HBF1V overexpression line.We demonstrate that the previously unknown gene,OsWRKY64,is a direct downstream target of HBF1 and represses flowering in rice,whereas three known flowering repressor genes,Days to heading 7(DTH7),CONSTANS 3(OsCO3),and OsWRKY104,are also direct target genes of HBF1 in flowering regulation.Taking these results together,we propose detailed molecular mechanisms by which HBF1 regulates the time to flower in rice.

Conservation of IRE1-Regulated bZIP74 mRNA Unconventional Splicing in Rice （Oryza sativa L.） Involved in ER Stress Responses

Protein folding in the endoplasmic reticulum （ER） is a fundamental process in plant cells that is vulnerable to many environmental stresses. When unfolded or misfolded proteins accumulate in the ER, the well-conserved unfolded protein response （UPR） is initiated to mitigate the ER stress by enhancing the protein folding capability and/or accelerating the ER-associated protein degradation. Here, we report the conservation of the activation mechanism of OsbZIP74 （also known as OsbZIP50）, an important ER stress regulator in monocot plant rice （Oryza sativa L.）. Under normal conditions, OsbZIP74 mRNA encodes a basic leucine-zipper transcription factor with a putative transmembrane domain. When treating with ER stress-inducing agents such as tunicamycin and DTT, the conserved double stem-loop structures of OsbZIP74 mRNA are spliced out. Thereafter, the resulting new OsbZIP74 mRNA produces the nucleus-localized form of OsbZIP74 protein, eliminating the hydrophobic region. The activated form of OsbZIP74 has transcriptional activation activity in both yeast cells and Arabidopsis leaf protoplasts. The induction of OsbZIP74 splicing is much suppressed in the OsIRE1 knock- down rice plants, indicating the involvement of OslRE1 in OsbZIP74 splicing. We also demonstrate that the unconventional splicing of OsbZIP74 mRNA is associated with heat stress and salicylic acid, which is an important plant hormone in systemic acquired resistance against pathogen or parasite.

A monocot-specific hydroxycinnamoylputrescine gene cluster contributes to immunity and cell death in rice

Phenolamides(PAs), a diverse group of specialized metabolites, including hydroxycinnamoylputrescine(HP), hydroxycinnamoylagmatine, and hydroxycinnamoyltryptamine, are important in plant resistance to biotic stress. However, the genes involved in the biosynthesis and modulation of PAs have not been fully elucidated. This study identified an HP biosynthetic gene cluster in rice(Oryza sativa) comprising one gene(Os ODC) encoding a decarboxylase and two tandem-duplicated genes(Os PHT3 and Os PHT4)encoding putrescine hydroxycinnamoyl acyltransferases coexpressed in different tissues. Os ODC catalyzes the conversion of ornithine to putrescine, which is used in HP biosynthesis involving Os PHT3 and Os PHT4. Os PHT3 or Os PHT4 overexpression causes HP accumulation and cell death and putrescine hydroxycinnamoyl acyltransferases(PHT) activity-dependent resistance against the fungal pathogen Magnaporthe oryzae. Os ODC overexpression plants also confer enhanced resistance to M. oryzae.Notably, the basic leucine zipper transcription factor APIP5, a negative regulator of cell death, directly binds to the Os PHT4 promoter, repressing its transcription. Moreover, APIP5 suppression induces Os PHT4 expression and HP accumulation. Comparative genomic analysis revealed that the HP biosynthetic gene cluster is conserved in monocots. These results characterized a previously unidentified monocot-specific gene cluster that is involved in HP biosynthesis and contributes to defense and cell death in rice.

Function of hydroxycinnamoyl transferases for the biosynthesis of phenolamides in rice resistance to Magnaporthe oryzae

Phenolamide(PA)metabolites play important roles in the interaction between plants and pathogens.The putrescine hydroxycinnamoyl transferase genes Os PHT3 and Os PHT4 positively regulate rice cell death and resistance to Magnaporthe oryzae.The b ZIP transcription factor APIP5,a negative regulator of cell death and rice immunity,directly binds to the Os PHT4 promoter to regulate putrescine-derived PAs.Whether other hydroxycinnamoyl transferase(HT)genes also participate in APIP5-mediated immunity remains unclear.Surprisingly,we find that genes encoding agmatine hydroxycinnamoyl transferases Os AHT1 and Os AHT2,tryptamine hydroxycinnamoyl transferases Os TBT1 and Os TBT2,and tyramine hydroxycinnamoyl transferases Os THT1 and Os THT2,responsible for the biosynthesis of polyamine-derived PAs are all up-regulated in APIP5-RNAi transgenic plants compared with segregated wild-type rice.Furthermore,both Os AHT1/2 and Os TBT1/2 are induced during M.oryzae infection,showing expression patterns similar to those previously reported for Os THT1/2 and Os PHT3/4.Transgenic plants overexpressing either Os AHT2-GFP or Os TBT1-GFP show enhanced resistance against M.oryzae and accumulated more PA metabolites and lignin compared with wild-type plants.Interestingly,as demonstrated for Os PHT4,APIP5 directly binds to the promoters of Os AHT1/2,Os TBT1/2,and Os THT1/2,repressing their transcription.Together,these results indicate that the HT genes are common targets of APIP5 and that PAs play critical roles in rice immunity.

Dysregulation of glutathione synthesis in liver disease

Glutathione(GSH),a tripeptide that is present in all mammalian tissues,is especially highly concentrated in the liver.GSH synthesis occurs via two adenosine triphosphate(ATP)-requiring enzymatic steps:the first is rate-limiting,catalyzed by glutamate-cysteine ligase,generates g-glutamylcysteine from gluta-mate and cysteine;the second is catalyzed by GSH synthetase,generates GSH from g-glutamylcysteine and glycine.GSH defends against oxidative stress,participates in detoxification of xenobiotics,de-termines the redox status of the cell,and regulates vital processes such as growth and apoptosis.Hepatic GSH plays a central role in the interorgan GSH homeostasis because sinusoidal efflux of hepatic GSH determines plasma GSH level.In liver diseases GSH homeostasis is perturbed by multiple mechanisms.Hepatic GSH biosynthesis is impaired in cholestatic liver injury,endotoxemia,and fibrotic injury largely because the expression of the GSH synthetic enzymes falls.Lower hepatic GSH level further exacerbates and perpetuates ongoing liver injury.However,in hepatocellular carcinoma GSH synthetic enzymes are upregulated and this may play a role in chemoresistance.This review focuses on the current under-standing of hepatic GSH synthesis in health and disease.