Regulation of metal homoeostasis by two F-group bZIP transcription factors bZIP48 and bZIP50 in rice.

Zinc (Zn) deficiency not only impairs plant growth and development but also has negative effects on human health. Rice (Oryza Sativa L.) is a staple food for over half of the global population, yet the regulation of Zn deficiency response in rice remains largely unknown. In this study, we provide evidence that two F-group bZIP transcription factors, OsbZIP48/50, play a crucial role in Zn deficiency response. Mutations in OsbZIP48/50 result in impaired growth and reduced Zn/Fe/Cu content under Zn deficiency conditions. The N-terminus of OsbZIP48/OsbZIP50 contains two Zn sensor motifs (ZSMs), deletion or mutation of these ZSMs leads to increased nuclear localization. Both OsbZIP48 and OsbZIP50 exhibit transcriptional activation activity, and the upregulation of 1117 genes involved in metal uptake and other processes by Zn deficiency is diminished in the OsbZIP48/50 double mutant. Both OsbZIP48 and OsbZIP50 bind to the promoter of OsZIP10 and activate the ZDRE cis-element. Amino acid substitution mutation of the ZSM domain of OsbZIP48 in OsbZIP50 mutant background increases the content of Zn/Fe/Cu in brown rice seeds and leaves. Therefore, this study demonstrates that OsbZIP48/50 play a crucial role in regulating metal homoeostasis and identifies their downstream genes involved in the Zn deficiency response in rice.

NFXL1 functions as a transcriptional activator required for thermotolerance at reproductive stage in Arabidopsis.

Plants are highly susceptible to abiotic stresses, particularly heat stress during the reproductive stage. However, the specific molecular mechanisms underlying this sensitivity remain largely unknown. In the current study, we demonstrate that the Nuclear Transcription Factor, X-box Binding Protein 1-Like 1 (NFXL1), directly regulates the expression of DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN 2A (DREB2A), which is crucial for reproductive thermotolerance in Arabidopsis. NFXL1 is upregulated by heat stress, and its mutation leads to a reduction in silique length (seed number) under heat stress conditions. RNA-Seq analysis reveals that NFXL1 has a global impact on the expression of heat stress responsive genes, including DREB2A, Heat Shock Factor A3 (HSFA3) and Heat Shock Protein 17.6 (HSP17.6) in flower buds. Interestingly, NFXL1 is enriched in the promoter region of DREB2A, but not of either HSFA3 or HSP17.6. Further experiments using electrophoretic mobility shift assay have confirmed that NFXL1 directly binds to the DNA fragment derived from the DREB2A promoter. Moreover, effector-reporter assays have shown that NFXL1 activates the DREB2A promoter. The DREB2A mutants are also heat stress sensitive at the reproductive stage, and DEREB2A is epistatic to NFXL1 in regulating thermotolerance in flower buds. It is known that HSFA3, a direct target of DREB2A, regulates the expression of heat shock proteins genes under heat stress conditions. Thus, our findings establish NFXL1 as a critical upstream regulator of DREB2A in the transcriptional cassette responsible for heat stress responses required for reproductive thermotolerance in Arabidopsis.

A competition-attenuation mechanism modulates thermoresponsive growth at warm temperatures in plants.

Global warming has profound impact on growth and development, and plants constantly adjust their internal circadian clock to cope with external environment. However, how clock-associated genes fine-tune thermoresponsive growth in plants is little understood. We found that loss-of-function mutation of REVEILLE5 (RVE5) reduces the expression of circadian gene EARLY FLOWERING 4 (ELF4) in Arabidopsis, and confers accelerated hypocotyl growth under warm-temperature conditions. Both RVE5 and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) accumulate at warm temperatures and bind to the same EE cis-element presented on ELF4 promoter, but the transcriptional repression activity of RVE5 is weaker than that of CCA1. The binding of CCA1 to ELF4 promoter is enhanced in the rve5-2 mutant at warm temperatures, and overexpression of ELF4 in the rve5-2 mutant background suppresses the rve5-2 mutant phenotype at warm temperatures. Therefore, the transcriptional repressor RVE5 finetunes ELF4 expression via competing at a cis-element with the stronger transcriptional repressor CCA1 at warm temperatures. Such a competition-attenuation mechanism provides a balancing system for modulating the level of ELF4 and thermoresponsive hypocotyl growth under warm-temperature conditions.

The hot science in rice research: How rice plants cope with heat stress.

Global climate change has great impacts on plant growth and development, reducing crop productivity worldwide. Rice (Oryza sativa L.), one of the world's most important food crops, is susceptible to high-temperature stress from seedling stage to reproductive stage. In this review, we summarize recent advances in understanding the molecular mechanisms underlying heat stress responses in rice, including heat sensing and signalling, transcriptional regulation, transcript processing, protein translation, and post-translational regulation. We also highlight the irreversible effects of high temperature on reproduction and grain quality in rice. Finally, we discuss challenges and opportunities for future research on heat stress responses in rice.

Histone H3K4 methyltransferases SDG25 and ATX1 maintain heat-stress gene expression during recovery in Arabidopsis.

Plants have short-term stress memory that enables them to maintain the expression state of a substantial subset of heat-inducible genes during stress recovery after heat stress. Little is known about the molecular mechanisms controlling stress-responsive gene expression at the recovery stage in plants, however. In this article, we demonstrate that histone H3K4 methyltransferases SDG25 and ATX1 are required for heat-stress tolerance in Arabidopsis. SDG25 and ATX1 are not only important for stress-responsive gene expression during heat stress, but also for maintaining stress-responsive gene expression during stress recovery. A combination of whole-genome bisulfite sequencing, RNA-sequencing and ChIP-qPCR demonstrated that mutations of SDG25 and ATX1 decrease histone H3K4me3 levels, increase DNA cytosine methylation and inhibit the expression of a subset of heat stress-responsive genes during stress recovery in Arabidopsis. ChIP-qPCR results confirm that ATX1 binds to chromatins associated with these target genes. Our results reveal that histone H3K4me3 affects DNA methylation at regions in the loci associated with heat stress-responsive gene expression during stress recovery, providing insights into heat-stress transcriptional memory in plants.

Ectopic overexpression of a membrane-tethered transcription factor gene NAC60 from oilseed rape positively modulates programmed cell death and age-triggered leaf senescence.

Senescence is an integrative final stage of plant development that is governed by internal and external cues. The NAM, ATAF1/2, CUC2 (NAC) transcription factor (TF) family is specific to plants and membrane-tethered NAC TFs (MTTFs) constitute a unique and sophisticated mechanism in stress responses and development. However, the function of MTTFs in oilseed rape (Brassica napus L.) remains unknown. Here, we report that BnaNAC60 is an MTTF associated with the endoplasmic reticulum (ER) membrane. Expression of BnaNAC60 was induced during the progression of leaf senescence. Translocation of BnaNAC60 into nuclei was induced by ER stress and oxidative stress treatments. It binds to the NTLBS motif, rather than the canonical NAC recognition site. Overexpression of BnaNAC60 devoid of the transmembrane domain, but not the full-length BnaNAC60, induces significant reactive oxygen species (ROS) accumulation and hypersensitive response-like cell death in both tobacco (Nicotiana benthamiana) and oilseed rape protoplasts. Moreover, ectopic overexpression of BnaNAC60 devoid of the transmembrane domain, but not the full-length BnaNAC60, in Arabidopsis also induces precocious leaf senescence. Furthermore, screening and expression profiling identified an array of functional genes that are significantly induced by BnaNAC60 expression. Further it was found that BnaNAC60 can activate the promoter activities of BnaNYC1, BnaRbohD, BnaBFN1, BnaZAT12, and multiple BnaVPEs in a dual-luciferase reporter assay. Electrophoretic mobility shift assay and chromatin immunoprecipitation coupled to quantitative PCR assays revealed that BnaNAC60 directly binds to the promoter regions of these downstream target genes. To summarize, our data show that BnaNAC60 is an MTTF that modulates cell death, ROS accumulation, and leaf senescence.

Regulation of Chloroplast Development and Function at Adverse Temperatures in Plants.

The chloroplast is essential for photosynthesis, plant growth and development. As semiautonomous organelles, the biogenesis and development of chloroplasts need to be well-regulated during plant growth and stress responses. Low or high ambient temperatures are adverse environmental stresses that affect crop growth and productivity. As sessile organisms, plants regulate the development and function of chloroplasts in a fluctuating temperature environment to maintain normal photosynthesis. This review focuses on the molecular mechanisms and regulatory factors required for chloroplast biogenesis and development under cold or heat stress conditions and highlights the importance of chloroplast gene transcription, RNA metabolism, ribosome function and protein homeostasis essential for chloroplast development under adverse temperature conditions.

An ABA-serotonin module regulates root suberization and salinity tolerance.

Suberin in roots acts as a physical barrier preventing water/mineral losses. In Arabidopsis, root suberization is regulated by abscisic acid (ABA) and ethylene in response to nutrient stresses. ABA also mediates coordination between microbiota and root endodermis in mineral nutrient homeostasis. However, it is not known whether this regulatory system is common to plants in general, and whether there are other key molecule(s) involved. We show that serotonin acts downstream of ABA in regulating suberization in rice and Arabidopsis and negatively regulates suberization in rice roots in response to salinity. We show that ABA represses transcription of the key gene (OsT5H) in serotonin biosynthesis, thus promoting root suberization in rice. Conversely, overexpression of OsT5H or supplementation with exogenous serotonin represses suberization and reduces tolerance to salt stress. These results identify an ABA-serotonin regulatory module controlling root suberization in rice and Arabidopsis, which is likely to represent a general mechanism as ABA and serotonin are ubiquitous in plants. These findings are of significant importance to breeding novel crop varieties that are resilient to abiotic stresses and developing strategies for production of suberin-rich roots to sequestrate more CO2 , helping to mitigate the effects of climate change.

BLISTER-regulated vegetative growth is dependent on the protein kinase domain of ER stress modulator IRE1A in Arabidopsis thaliana.

The unfolded protein response (UPR) is required for protein homeostasis in the endoplasmic reticulum (ER) when plants are challenged by adverse environmental conditions. Inositol-requiring enzyme 1 (IRE1), the bifunctional protein kinase / ribonuclease, is an important UPR regulator in plants mediating cytoplasmic splicing of the mRNA encoding the transcription factor bZIP60. This activates the UPR signaling pathway and regulates canonical UPR genes. However, how the protein activity of IRE1 is controlled during plant growth and development is largely unknown. In the present study, we demonstrate that the nuclear and Golgi-localized protein BLISTER (BLI) negatively controls the activity of IRE1A/IRE1B under normal growth condition in Arabidopsis. Loss-of-function mutation of BLI results in chronic up-regulation of a set of both canonical UPR genes and non-canonical UPR downstream genes, leading to cell death and growth retardation. Genetic analysis indicates that BLI-regulated vegetative growth phenotype is dependent on IRE1A/IRE1B but not their canonical splicing target bZIP60. Genetic complementation with mutation analysis suggests that the D570/K572 residues in the ATP-binding pocket and N780 residue in the RNase domain of IRE1A are required for the activation of canonical UPR gene expression, in contrast, the D570/K572 residues and D590 residue in the protein kinase domain of IRE1A are important for the induction of non-canonical UPR downstream genes in the BLI mutant background, which correlates with the shoot growth phenotype. Hence, our results reveal the important role of IRE1A in plant growth and development, and BLI negatively controls IRE1A's function under normal growth condition in plants.

Organophosphorus Flame Retardant TCPP Induces Cellular Senescence in Normal Human Skin Keratinocytes: Implication for Skin Aging.

Tris (1-chloro-2-propyl) phosphate (TCPP) is one of the most frequently detected organophosphorus flames in the environment. Continuous daily exposure to TCPP may harm human skin. However, little is known about the adverse effects of TCPP on human skin. In this study, we first evaluated the detrimental effects and tried to uncover the underlying mechanisms of TCPP on human skin keratinocytes (HaCaT) after 24 h exposure. We found that TCPP caused a concentration-dependent decrease in HaCaT cell viability after exposure to 1.56-400 µg/mL for 24 h, with an IC50 of 275 µg/mL. TCPP also promoted the generation of intracellular reactive oxygen species (ROS) and triggered DNA damage, evidenced by an increase of phosphorylated histone H2A.X (γH2A.X) in the nucleus. Furthermore, the cell cycle was arrested at the G1 phase at 100 µg/mL by upregulation of the mRNA expression of p53 and p21 and downregulation of cyclin D1 and CDK4 expression. Additionally, both the senescence-associated-ß-galactosidase activity and related proinflammatory cytokine IL-1ß and IL-6 were elevated, indicating that TCPP exposure caused cellular senescence may be through the p53-dependent DNA damage signal pathway in HaCaT cells. Taken together, our data suggest that flame-retardant exposure may be a key precipitating factor for human skin aging.

UBA domain protein SUF1 interacts with NatA-complex subunit NAA15 to regulate thermotolerance in Arabidopsis.

During recovery from heat stress, plants clear away the heat-stress-induced misfolded proteins through the ubiquitin-proteasome system (UPS). In the UPS, the recognition of substrate proteins by E3 ligase can be regulated by the N-terminal acetyltransferase A (NatA) complex. Here, we determined that Arabidopsis STRESS-RELATED UBIQUITIN-ASSOCIATED-DOMAIN PROTEIN FACTOR 1 (SUF1) interacts with the NatA complex core subunit NAA15 and positively regulates NAA15. The suf1 and naa15 mutants are sensitive to heat stress; the NatA substrate N SNC1 is stabilized in suf1 mutant plants during heat stress recovery. Therefore, SUF1 and its interactor NAA15 play important roles in basal thermotolerance in Arabidopsis.

REVEILLE 7 inhibits the expression of the circadian clock gene EARLY FLOWERING 4 to fine-tune hypocotyl growth in response to warm temperatures.

The circadian clock maintains the daily rhythms of plant growth and anticipates predictable ambient temperature cycles. The evening complex (EC), comprising EARLY FLOWERING 3 (ELF3), ELF4, and LUX ARRHYTHMO, plays an essential role in suppressing thermoresponsive hypocotyl growth by negatively regulating PHYTOCHROME INTERACTING FACTOR 4 (PIF4) activity and its downstream targets in Arabidopsis thaliana. However, how EC activity is attenuated by warm temperatures remains unclear. Here, we demonstrate that warm temperature-induced REVEILLE 7 (RVE7) fine-tunes thermoresponsive growth in Arabidopsis by repressing ELF4 expression. RVE7 transcript and RVE7 protein levels increased in response to warm temperatures. Under warm temperature conditions, an rve7 loss-of-function mutant had shorter hypocotyls, while overexpressing RVE7 promoted hypocotyl elongation. PIF4 accumulation and downstream transcriptional effects were reduced in the rve7 mutant but enhanced in RVE7 overexpression plants under warm conditions. RVE7 associates with the Evening Element in the ELF4 promoter and directly represses its transcription. ELF4 is epistatic to RVE7, and overexpressing ELF4 suppressed the phenotype of the RVE7 overexpression line under warm temperature conditions. Together, our results identify RVE7 as an important regulator of thermoresponsive growth that functions (in part) by controlling ELF4 transcription, highlighting the importance of ELF4 for thermomorphogenesis in plants.

Two B-box domain proteins, BBX28 and BBX29, regulate flowering time at low ambient temperature in Arabidopsis.

KEY MESSAGE: This paper demonstrates that BBX28 and BBX29 proteins in Arabidopsis promote flowering in association with the CO-FT regulatory module at low ambient temperature under LD conditions. Flowering plants integrate internal developmental signals with external environmental stimuli for precise flowering time control. The expression of BBX29 is up-regulated by low temperature treatment, but the biological function of BBX29 in low temperature response is unknown. In the current study, we examined the biological role of BBX29 and its close-related protein BBX28 in flowering time control under long-day conditions. Although neither BBX28 single mutant nor BBX29 single mutant has a flowering-associated phenotype, the bbx28 bbx29 double mutant plants have an obvious delayed flowering phenotype grown at low ambient temperature (16°C) compared to the wild-type (WT) plants. The expression of FT and TSF was lower in bbx28 bbx29 double mutant plants than in wild-type plants at 16°C. Both BBX28 and BBX29 interact with CONSTANS (CO), an important flowering integrator that directly binds to the FLOWERING LOCUS T (FT) promoter. In the effector-reporter assays, transcriptional activation activity of CO on the FT promoter was reduced in bbx28 bbx29 double mutant plants compared to that in WT plants. Taken together, our results reveal that BBX28 and BBX29 are promoters of flowering in Arabidopsis, especially at low ambient temperature.

Chromatin remodeling factors regulate environmental stress responses in plants.

Environmental stress from climate change and agricultural activity threatens global plant biodiversity as well as crop yield and quality. As sessile organisms, plants must maintain the integrity of their genomes and adjust gene expression to adapt to various environmental changes. In eukaryotes, nucleosomes are the basic unit of chromatin around which genomic DNA is packaged by condensation. To enable dynamic access to packaged DNA, eukaryotes have evolved Snf2 (sucrose nonfermenting 2) family proteins as chromatin remodeling factors (CHRs) that modulate the position of nucleosomes on chromatin. During plant stress responses, CHRs are recruited to specific genomic loci, where they regulate the distribution or composition of nucleosomes, which in turn alters the accessibility of these loci to general transcription or DNA damage repair machinery. Moreover, CHRs interplay with other epigenetic mechanisms, including DNA methylation, histone modifications, and deposition of histone variants. CHRs are also involved in RNA processing at the post-transcriptional level. In this review, we discuss major advances in our understanding of the mechanisms by which CHRs function during plants' response to environmental stress.

The E3 ligase XBAT35 mediates thermoresponsive hypocotyl growth by targeting ELF3 for degradation in Arabidopsis.

Plants are capable of coordination of their growth and development with ambient temperatures. EARLY FLOWERING3 (ELF3), an essential component of the plant circadian clock, is also involved in ambient temperature sensing, as well as in inhibiting the expression and protein activity of the thermoresponsive regulator phytochrome interacting factor 4 (PIF4). The ELF3 activity is subjected to attenuation in response to warm temperature; however, how the protein level of ELF3 is regulated at warm temperature remains less understood. Here, we report that the E3 ligase XB3 ORTHOLOG 5 IN ARABIDOPSIS THALIANA, XBAT35, mediates ELF3 degradation. XBAT35 interacts with ELF3 and ubiquitinates ELF3. Loss-of-function mutation of XBAT35 increases the protein level of ELF3 and confers a short-hypocotyl phenotype under warm temperature conditions. Thus, our findings establish that XBAT35 mediates ELF3 degradation to lift the inhibition of ELF3 on PIF4 for promoting thermoresponsive hypocotyl growth in plants.

NAC103, a NAC family transcription factor, regulates ABA response during seed germination and seedling growth in Arabidopsis.

MAIN CONCLUSION: The Arabidopsis transcription factor NAC103 is up-regulated and its encoding protein is stabilized by ABA treatment, which positively regulates several ABA-responsive downstream genes during seed germination and seedlings growth. The Arabidopsis transcription factor NAC103 was previously found to be involved in endoplasmic reticulum (ER) stress and DNA damage responses. In this study, we report the new biological function of NAC103 in abscisic acid (ABA) response during seed germination and seedling growth in Arabidopsis. The expression of NAC103 was up-regulated and the NAC103 protein was stabilized by ABA treatment. Both the loss-of-function mutants of NAC103, created by targeted gene-editing, and the over-expression plants of NAC103 have no obvious germination-related phenotype under normal growth conditions. However, under exogenous ABA treatment conditions, the NAC103 mutants were less sensitive to ABA during seed germination; in contrast, the NAC103 over-expression plants were more sensitive to ABA during seed germination and young seedling growth. Further, NAC103 regulated several ABA-responsive downstream genes including MYB78, MYB3, PLP3, AMY1, and RGL2. These results demonstrate that NAC103 positively regulates ABA response in Arabidopsis.

A membrane-associated NAC transcription factor OsNTL3 is involved in thermotolerance in rice.

Heat stress induces misfolded protein accumulation in endoplasmic reticulum (ER), which initiates the unfolded protein response (UPR) in plants. Previous work has demonstrated the important role of a rice ER membrane-associated transcription factor OsbZIP74 (also known as OsbZIP50) in UPR. However, how OsbZIP74 and other membrane-associated transcription factors are involved in heat stress tolerance in rice is not reported. In the current study, we discovered that OsNTL3 is required for heat stress tolerance in rice. OsNTL3 is constitutively expressed and up-regulated by heat and ER stresses. OsNTL3 encodes a NAC transcription factor with a predicted C-terminal transmembrane domain. GFP-OsNTL3 relocates from plasma membrane to nucleus in response to heat stress and ER stress inducers. Loss-of-function mutation of OsNTL3 confers heat sensitivity while inducible expression of the truncated form of OsNTL3 without the transmembrane domain increases heat tolerance in rice seedlings. RNA-Seq analysis revealed that OsNTL3 regulates the expression of genes involved in ER protein folding and other processes. Interestingly, OsNTL3 directly binds to OsbZIP74 promoter and regulates its expression in response to heat stress. In turn, up-regulation of OsNTL3 by heat stress is dependent on OsbZIP74. Thus, our work reveals the important role of OsNTL3 in thermotolerance, and a regulatory circuit mediated by OsbZIP74 and OsNTL3 in communications among ER, plasma membrane and nucleus under heat stress conditions.

Tissue-Specific Transcriptomics Reveals an Important Role of the Unfolded Protein Response in Maintaining Fertility upon Heat Stress in Arabidopsis.

High temperatures have a great impact on plant reproductive development and subsequent fruit and seed set, but the underlying molecular mechanisms are not well understood. We used transcriptome profiling to investigate the effect of heat stress on reproductive development of Arabidopsis thaliana plants and observed distinct response patterns in vegetative versus reproductive tissues. Exposure to heat stress affected reproductive developmental programs, including early phases of anther/ovule development and meiosis. Also, genes participating in the unfolded protein response (UPR) were enriched in the reproductive tissue-specific genes that were upregulated by heat. Moreover, we found that the UPR-deficient bzip28 bzip60 double mutant was sensitive to heat stresses and had reduced silique length and fertility. Comparison of heat-responsive wild type versus bzip28 bzip60 plants identified 521 genes that were regulated by bZIP28 and bZIP60 upon heat stress during reproductive stages, most of which were noncanonical UPR genes. Chromatin immunoprecipitation coupled with high-throughput sequencing analyses revealed 133 likely direct targets of bZIP28 in Arabidopsis seedlings subjected to heat stress, including 27 genes that were also upregulated by heat during reproductive development. Our results provide important insights into heat responsiveness in Arabidopsis reproductive tissues and demonstrate the protective roles of the UPR for maintaining fertility upon heat stress.

Quantitative Proteomic Analysis of ER Stress Response Reveals both Common and Specific Features in Two Contrasting Ecotypes of Arabidopsis thaliana.

Accumulation of unfolded and misfolded proteins in endoplasmic reticulum (ER) elicits a well-conserved response called the unfolded protein response (UPR), which triggers the upregulation of downstream genes involved in protein folding, vesicle trafficking, and ER-associated degradation (ERAD). Although dynamic transcriptomic responses and the underlying major transcriptional regulators in ER stress response in Arabidopsis have been well established, the proteome changes induced by ER stress have not been reported in Arabidopsis. In the current study, we found that the Arabidopsis Landsberg erecta (Ler) ecotype was more sensitive to ER stress than the Columbia (Col) ecotype. Quantitative mass spectrometry analysis with Tandem Mass Tag (TMT) isobaric labeling showed that, in total, 7439 and 7035 proteins were identified from Col and Ler seedlings, with 88 and 113 differentially regulated (FC > 1.3 or <0.7, p < 0.05) proteins by ER stress in Col and Ler, respectively. Among them, 40 proteins were commonly upregulated in Col and Ler, among which 10 were not upregulated in bzip28 bzip60 double mutant (Col background) plants. Of the 19 specifically upregulated proteins in Col, as compared with that in Ler, components in ERAD, N-glycosylation, vesicle trafficking, and molecular chaperones were represented. Quantitative RT-PCR showed that transcripts of eight out of 19 proteins were not upregulated (FC > 1.3 or <0.7, p < 0.05) by ER stress in Col ecotype, while transcripts of 11 out of 19 proteins were upregulated by ER stress in both ecotypes with no obvious differences in fold change between Col and Ler. Our results experimentally demonstrated the robust ER stress response at the proteome level in plants and revealed differentially regulated proteins that may contribute to the differed ER stress sensitivity between Col and Ler ecotypes in Arabidopsis.

The ß5 subunit is essential for intact 26S proteasome assembly to specifically promote plant autotrophic growth under salt stress.

The ubiquitin 26S proteasome (26SP) system efficiently degrades many key regulators of plant development. 26SP consists of two subcomplexes: the catalytic 20S core particle (CP) and the 19S regulatory particle (RP). Previous studies have focused on 19S RP; whether there is a specific subunit in 20S CP that has a stress-related biological function in plants is unclear. PBE1, one of the ß5 subunits of Arabidopsis proteasome CP, is essential for the assembly and proteolytic activity of 26SP in salt-stressed seedlings. The expression of PBE1 is stress-induced. During the transition from seed germination to autotrophic growth in salt-stressed seedlings, loss of PBE1 function results specifically in arrest in developmental transition but not in germination and post-germination growth. PBE1 is also important for other types of proteasome stress and Endoplasmic Reticulum (ER) stress. PBE1 modulates the protein level of the transcription factor ABI5 and thereby down-regulates the expression of several genes downstream of this key regulator which are known to be essential for plant growth under stress. Collectively, our results showed PBE1-mediated intact proteasome assembly that is essential for successful autotrophic growth, and revealed how PBE1 mediated stress proteasome functions to control both proteasome activity and abscisic acid (ABA)-mediated stress signaling in plants.