Multiprotein Bridging Factor 1c Research Articles

A lily heat-inducible multi-protein bridging factor, LlMBF1c, plays a crucial role in plant thermotolerance

Lily (Lilium spp.) is popular for its colorful flowers and exquisite scents. Nonetheless, high temperatures often severely reduce its yield production and quality. The implementation of biotechnological approaches to manipulate the expression of key heat-resistant genes is an effective way to improve the thermotolerance of plants. Here, we isolated a gene encoding for a multi-protein bridging factor 1c (MBF1c) from L. longiflorum 'White Heaven' (LlMBF1c), which was highly similar to MBF1c from Elaeis guineensis (EgMBF1c). LlMBF1c harbors conserved MBF1 and helix-turn-helix (HTH) domains. Moreover, the expression of LlMBF1c and its promoter activity were enhanced under high-temperature conditions. Further analysis indicated that LlMBF1c is a transcriptional repressor in both yeast and Nicotiana benthamiana. Its protein was located in the nucleus and cytoplasm of N. benthamiana leaf cells. Overexpression of LlMBF1c in lily and Arabidopsis resulted in enhanced thermotolerance in these plants. By contrast, silencing LlMBF1c reduced the thermotolerance of lily. Our results identified an important candidate gene that can be utilized to develop thermotolerant lily germplasm.

HD-Zip I protein LlHOX6 antagonizes homeobox protein LlHB16 to attenuate basal thermotolerance in lily.

Homeodomain-leucine zipper (HD-Zip) I transcription factors are crucial for plant responses to drought, salt, and cold stresses. However, how they are associated with thermotolerance remains mostly unknown. We previously demonstrated that lily (Lilium longiflorum) LlHB16 (HOMEOBOX PROTEIN 16) promotes thermotolerance, whereas the roles of other HD-Zip I members are still unclear. Here, we conducted a transcriptomic analysis and identified a heat-responsive HD-Zip I gene, LlHOX6 (HOMEOBOX 6). We showed that LlHOX6 represses the establishment of basal thermotolerance in lily. LlHOX6 expression was rapidly activated by high temperature, and its protein localized to the nucleus. Heterologous expression of LlHOX6 in Arabidopsis (Arabidopsis thaliana) and overexpression in lily reduced their basal thermotolerance. In contrast, silencing LlHOX6 in lily elevated basal thermotolerance. Cooverexpressing or cosilencing LlHOX6 and LlHB16 in vivo compromised their functions in modulating basal thermotolerance. LlHOX6 interacted with itself and with LlHB16, although heterologous interactions were stronger than homologous ones. Notably, LlHOX6 directly bounds DNA elements to repress the expression of the LlHB16 target genes LlHSFA2 (HEAT STRESS TRANSCRIPTION FACTOR A2) and LlMBF1c (MULTIPROTEIN BRIDGING FACTOR 1C). Moreover, LlHB16 activated itself to form a positive feedback loop, while LlHOX6 repressed LlHB16 expression. The LlHOX6-LlHB16 heterooligomers exhibited stronger DNA binding to compete for LlHB16 homooligomers, thus weakening the transactivation ability of LlHB16 for LlHSFA2 and LlMBF1c and reducing its autoactivation. Altogether, our findings demonstrate that LlHOX6 interacts with LlHB16 to limit its transactivation, thereby impairing heat stress responses in lily.

A long noncoding RNA HILinc1 enhances pear thermotolerance by stabilizing PbHILT1 transcripts through complementary base pairing

As global warming intensifies, heat stress has become a major environmental constraint threatening crop production and quality worldwide. Here, we characterize Heat-induced long intergenic noncoding RNA 1 (HILinc1), a cytoplasm-enriched lincRNA that plays a key role in thermotolerance regulation of pear (Pyrus spp.). HILinc1 Target 1 (PbHILT1) which is the target transcript of HILinc1, was stabilized via complementary base pairing to upregulate its expression. PbHILT1 could bind to Heat shock transcription factor A1b (PbHSFA1b) to enhance its transcriptional activity, leading to the upregulation of a major downstream transcriptional regulator, Multiprotein bridging factor 1c (PbMBF1c), during heat response. Transient overexpressing of either HILinc1 or PbHILT1 increases thermotolerance in pear, while transient silencing of HILinc1 or PbHILT1 makes pear plants more heat sensitive. These findings provide evidences for a new regulatory mechanism by which HILinc1 facilitates PbHSFA1b activity and enhances pear thermotolerance through stabilizing PbHILT1 transcripts.

Regulation and physiological function of proteins for heat tolerance in cowpea (Vigna unguiculata) genotypes under controlled and field conditions.

The expression of heat shock proteins is considered a central adaptive mechanism to heat stress. This study investigated the expression of heat shock proteins (HSPs) and other stress-protective proteins against heat stress in cowpea genotypes under field (IT-96D-610 and IT-16) and controlled (IT-96D-610) conditions. Heat stress response analysis of proteins at 72 h in the controlled environment showed 270 differentially regulated proteins identified using label-free quantitative proteomics in IT-96D-610 plants. These plants expressed HSPs and chaperones [BAG family molecular chaperone 6 (BAG6), Multiprotein bridging factor1c (MBF1C) and cold shock domain protein 1 (CSDP1) in the controlled environment]. However, IT-96D-610 plants expressed a wider variety of small HSPs and more HSPs in the field. IT-96D-610 plants also responded to heat stress by exclusively expressing chaperones [DnaJ chaperones, universal stress protein and heat shock binding protein (HSBP)] and non-HSP proteins (Deg1, EGY3, ROS protective proteins, temperature-induced lipocalin and succinic dehydrogenase). Photosynthesis recovery and induction of proteins related to photosynthesis were better in IT-96D-610 because of the concurrent induction of heat stress response proteins for chaperone functions, protein degradation for repair and ROS scavenging proteins and PSII operating efficiency (Fq’/Fm′) than IT-16. This study contributes to identification of thermotolerance mechanisms in cowpea that can be useful in knowledge-based crop improvement.

The transcriptional coactivator CmMBF1c is required for waterlogging tolerance in Chrysanthemum morifolium.

Waterlogging is one of the most serious abiotic stressors affecting Chrysanthemum morifolium during its lifespan. However, the molecular mechanisms underlying the waterlogging tolerance of chrysanthemum remain unclear. In this study, we discovered that the transcriptional coactivator MULTIPROTEIN BRIDGING FACTOR 1c (CmMBF1c) was significantly induced by waterlogging stress in chrysanthemums. Promoter sequence analysis and transient dual-luciferase assay using chrysanthemum protoplasts showed that the waterlogging-tolerant cultivar 'Nannongxuefeng' carried more response elements involved in waterlogging and hypoxia stress compared with the waterlogging-sensitive cultivar 'Qinglu', conferring on 'Nannongxuefeng' a stronger hypoxia responsive activity and higher CmMBF1c expression under waterlogging conditions. Subcellular localization and transcriptional activity assays showed that CmMBF1c protein was localized to the nucleus and had no transcriptional activation activity. Overexpression of CmMBF1c in 'Qinglu' enhanced its waterlogging tolerance by promoting its reactive oxygen species (ROS) scavenging ability and maintaining low ROS levels. However, RNAi-mediated knockdown of CmMBF1c in cultivar 'Nannongxuefeng' resulted in the opposite tendency. Yeast two-hybrid screening and tobacco bimolecular fluorescence complementation assays revealed that CmHRE2, a pivotal regulator of hypoxia response, could interact with CmMBF1c. In summary, this study demonstrates that CmMBF1c improves chrysanthemum waterlogging tolerance by regulating its ROS signaling pathway and interacting with CmHRE2. These findings together offer, to our knowledge, new mechanistic insights into chrysanthemum waterlogging tolerance and provide a rational foundation for future research on the genetic improvement of horticultural crops for waterlogging stress tolerance.

Trehalose phosphate synthase 5-dependent trehalose metabolism modulates basal defense responses in Arabidopsis thaliana.

Despite the recent discovery that trehalose synthesis is important for plant development and abiotic stress tolerance, the effects of trehalose on biotic stress responses remain relatively unknown. In this study, we demonstrate that TREHALOSE PHOSPHATE SYNTHASE 5 (TPS5)-dependent trehalose metabolism regulates Arabidopsis thaliana defenses against pathogens (necrotrophic Botrytis cinerea and biotrophic Pseudomonas syringae). Pathogen infection increased trehalose levels and upregulated TPS5 expression. Application of exogenous trehalose significantly improved plant defenses against B. cinerea, but increased the susceptibility of plants to P. syringae. We demonstrate that elevated trehalose biosynthesis, in transgenic plants over-expressing TPS5, also increased the susceptibility to P. syringae, but decreased the disease symptoms caused by B. cinerea. The knockout of TPS5 prevented the accumulation of trehalose and enhanced defense responses against P. syringae. Additionally, we observed that a TPS5-interacting protein (multiprotein bridging factor 1c) was required for induced expression of TPS5 during pathogen infections. Furthermore, we show that trehalose promotes P. syringae growth and disease development, via a mechanism involving suppression of the plant defense gene, Pathogenesis-Related Protein 1. These findings provide insight into the function of TPS5-dependent trehalose metabolism in plant basal defense responses.

Transcriptomic analysis reveals unique molecular factors for lipid hydrolysis, secondary cell-walls and oxidative protection associated with thermotolerance in perennial grass

BackgroundHeat stress is the primary abiotic stress limiting growth of cool-season grass species. The objective of this study was to determine molecular factors and metabolic pathways associated with superior heat tolerance in thermal bentgrass (Agrostis scabra) by comparative analysis of transcriptomic profiles with its co-generic heat-sensitive species creeping bentgrass (A. stolonifera).ResultsTranscriptomic profiling by RNA-seq in both heat-sensitive A. stolonifera (cv. ‘Penncross’) and heat-tolerant A. scabra exposed to heat stress found 1393 (675 up- and 718 down-regulated) and 1508 (777 up- and 731 down-regulated) differentially-expressed genes, respectively. The superior heat tolerance in A. scabra was associated with more up-regulation of genes in oxidative protection, proline biosynthesis, lipid hydrolysis, hemicellulose and lignin biosynthesis, compared to heat-sensitive A. stolonifera. Several transcriptional factors (TFs), such as high mobility group B protein 7 (HMGB7), dehydration-responsive element-binding factor 1a (DREB1a), multiprotein-bridging factor 1c (MBF1c), CCCH-domain containing protein 47 (CCCH47), were also found to be up-regulated in A. scabra under heat stress.ConclusionsThe unique TFs and genes identified in thermal A. scabra could be potential candidate genes for genetic modification of cultivated grass species for improving heat tolerance, and the associated pathways could contribute to the transcriptional regulation for superior heat tolerance in bentgrass species.

Differences between seedlings and flowers in anti-ROS based heat responses of Arabidopsis plants deficient in cyclic nucleotide gated channel 2

Cyclic nucleotide gated channel 2 (CNGC2) in Arabidopsis has been identified as one of the putative heat sensors which might play a key role in the regulation of heat acclimation. However, it is still not understood how CNGC2 controls heat stress responses during different growth stages. This study aimed to characterize the differences in heat stress responses between seedlings and flowers of Arabidopsis plants deficient in CNGC2. Seedlings of Arabidopsis plants deficient in CNGC2 showed enhanced tolerance to heat stress accompanied by higher accumulation of heat response proteins such as multiprotein bridging factor 1c (MBF1c), ascorbate peroxidases (APXs) and heat shock proteins (HSPs). On the other hand, seed production of these knockout lines was more sensitive to heat stress. In contrast to seedlings, accumulation of MBF1c and APX proteins in flowers of these knockout lines was lower than or almost comparable with that in WT plants under heat stress. In addition, plants deficient in CNGC2 showed dramatically higher accumulation of H2O2 in flowers, but, only slightly higher accumulation in seedlings compared with WT plants. These results suggest that the stage-dependent differences in heat stress response of Arabidopsis regulated by CNGC2 might rely on regulatory mechanisms of APX1-and MBF1c-dependent pathways and H2O2 homeostasis.

Antarctic Moss Multiprotein Bridging Factor 1c Overexpression in Arabidopsis Resulted in Enhanced Tolerance to Salt Stress.

Polytrichastrum alpinum is one of the moss species that survives extreme conditions in the Antarctic. In order to explore the functional benefits of moss genetic resources, P. alpinum multiprotein-bridging factor 1c gene (PaMBF1c) was isolated and characterized. The deduced amino acid sequence of PaMBF1c comprises of a multiprotein-bridging factor (MBF1) domain and a helix-turn-helix (HTH) domain. PaMBF1c expression was induced by different abiotic stresses in P. alpinum, implying its roles in stress responses. We overexpressed PaMBF1c in Arabidopsis and analyzed the resulting phenotypes in comparison with wild type and/or Arabidopsis MBF1c (AtMBF1c) overexpressors. Overexpression of PaMBF1c in Arabidopsis resulted in enhanced tolerance to salt and osmotic stress, as well as to cold and heat stress. More specifically, enhanced salt tolerance was observed in PaMBF1c overexpressors in comparison to wild type but not clearly observable in AtMBF1c overexpressing lines. Thus, these results implicate the evolution of PaMBF1c under salt-enriched Antarctic soil. RNA-Seq profiling of NaCl-treated plants revealed that 10 salt-stress inducible genes were already up-regulated in PaMBF1c overexpressing plants even before NaCl treatment. Gene ontology enrichment analysis with salt up-regulated genes in each line uncovered that the terms lipid metabolic process, ion transport, and cellular amino acid biosynthetic process were significantly enriched in PaMBF1c overexpressors. Additionally, gene enrichment analysis with salt down-regulated genes in each line revealed that the enriched categories in wild type were not significantly overrepresented in PaMBF1c overexpressing lines. The up-regulation of several genes only in PaMBF1c overexpressing lines suggest that enhanced salt tolerance in PaMBF1c-OE might involve reactive oxygen species detoxification, maintenance of ATP homeostasis, and facilitation of Ca2+ signaling. Interestingly, many salt down-regulated ribosome- and translation-related genes were not down-regulated in PaMBF1c overexpressing lines under salt stress. These differentially regulated genes by PaMBF1c overexpression could contribute to the enhanced tolerance in PaMBF1c overexpressing lines under salt stress.

Arabidopsis heat stress transcription factors A2 (HSFA2) and A3 (HSFA3) function in the same heat regulation pathway

Heat stress transcription factors (HSFs) play an essential role in the adjustment of plants to high temperatures. These molecules have evolved complicated mechanisms that rely on interactions between different HSFs and other heat stress-related genes [such as bZIP28, multiprotein bridging factor 1c (MBF1c), calmodulin-binding protein kinase 3 (CBK3)] in response to different heat stresses (such as occasional or successive high temperatures). In the present study, phenotypic, gene expression and yeast two-hybrid assays revealed that HSFA2 and HSFA3 function in the same heat regulation pathway. The single mutants, hsfa2 and hsfa3 as well as double mutant hsfa2 and hsfa3, exhibited heat-sensitive phenotypes in acquired thermotolerance after a long recovery time (ATLR) but not in basic thermotolerance and acquired thermotolerance after a short recovery time (ATSR). The expression of HSP18.1-CI and HSP25.3-P was down-regulated in single and double mutants of hsfa2 and hsfa3 under successive heat stress in ATLR assays. In addition, HSFA2 interacted with HSFA3 at the protein level in yeast two-hybrid assays. These results demonstrated dynamic alterations in the expression of HSFA2, HSFA3 and other heat-related genes in ATLR assays, providing new insights into the relationship between HSFA2 and HSFA3; this information will refine the HSF network in the regulation of heat stress response.

Integrating Omics and Alternative Splicing Reveals Insights into Grape Response to High Temperature.

Heat stress is one of the primary abiotic stresses that limit crop production. Grape (Vitis vinifera) is a cultivated fruit with high economic value throughout the world, with its growth and development often influenced by high temperature. Alternative splicing (AS) is a widespread phenomenon increasing transcriptome and proteome diversity. We conducted high-temperature treatments (35°C, 40°C, and 45°C) on grapevines and assessed transcriptomic (especially AS) and proteomic changes in leaves. We found that nearly 70% of the genes were alternatively spliced under high temperature. Intron retention (IR), exon skipping, and alternative donor/acceptor sites were markedly induced under different high temperatures. Among all differential AS events, IR was the most abundant up- and down-regulated event. Moreover, the occurrence frequency of IR events at 40°C and 45°C was far higher than at 35°C. These results indicated that AS, especially IR, is an important posttranscriptional regulatory event during grape leaf responses to high temperature. Proteomic analysis showed that protein levels of the RNA-binding proteins SR45, SR30, and SR34 and the nuclear ribonucleic protein U1A gradually rose as ambient temperature increased, which revealed a reason why AS events occurred more frequently under high temperature. After integrating transcriptomic and proteomic data, we found that heat shock proteins and some important transcription factors such as MULTIPROTEIN BRIDGING FACTOR1c and HEAT SHOCK TRANSCRIPTION FACTOR A2 were involved mainly in heat tolerance in grape through up-regulating transcriptional (especially modulated by AS) and translational levels. To our knowledge, these results provide the first evidence for grape leaf responses to high temperature at simultaneous transcriptional, posttranscriptional, and translational levels.

ABA is required for the accumulation of APX1 and MBF1c during a combination of water deficit and heat stress.

Abscisic acid (ABA) plays a key role in plant acclimation to abiotic stress. Although recent studies suggested that ABA could also be important for plant acclimation to a combination of abiotic stresses, its role in this response is currently unknown. Here we studied the response of mutants impaired in ABA signalling (abi1-1) and biosynthesis (aba1-1) to a combination of water deficit and heat stress. Both mutants displayed reduced growth, biomass, and survival when subjected to stress combination. Focusing on abi1-1, we found that although its stomata had an impaired response to water deficit, remaining significantly more open than wild type, its stomatal aperture was surprisingly reduced when subjected to the stress combination. Stomatal closure during stress combination in abi1-1 was accompanied by higher levels of H2O2 in leaves, suggesting that H2O2 might play a role in this response. In contrast to the almost wild-type stomatal closure phenotype of abi1-1 during stress combination, the accumulation of ascorbate peroxidase 1 and multiprotein bridging factor 1c proteins, required for acclimation to a combination of water deficit and heat stress, was significantly reduced in abi1-1 Our findings reveal a key function for ABA in regulating the accumulation of essential proteins during a combination of water deficit and heat stress.

Histone acetyltransferase GCN5 is essential for heat stress-responsive gene activation and thermotolerance in Arabidopsis.

Exposure to temperatures exceeding the normal optimum levels, or heat stress (HS), constitutes an environmental disruption for plants, resulting in severe growth and development retardation. Here we show that loss of function of the Arabidopsis histone acetyltransferase GCN5 results in serious defects in terms of thermotolerance, and considerably impairs the transcriptional activation of HS-responsive genes. Notably, expression of several key regulators such as the HS transcription factors HSFA2 and HSFA3, Multiprotein Bridging Factor 1c (MBF1c) and UV-HYPERSENSITIVE 6 (UVH6) is down-regulated in the gcn5 mutant under HS compared with the wild-type. Chromatin immunoprecipitation (ChIP) assays indicated that GCN5 protein is enriched at the promoter regions of HSFA3 and UVH6 genes, but not in HSFA2 and MBF1c, and that GCN5 facilitates H3K9 and H3K14 acetylation, which are associated with HSFA3 and UVH6 activation under HS. Moreover, constitutive expression of UVH6 in the gcn5 mutant partially restores heat tolerance. Taken together, our data indicate that GCN5 plays a key role in the preservation of thermotolerance via versatile regulation in Arabidopsis. In addition, expression of the wheat TaGCN5 gene re-establishes heat tolerance in Arabidopsis gcn5 mutant plants, suggesting that GCN5-mediated thermotolerance may be conserved between Arabidopsis and wheat.

Overexpression of heat stress-responsive TaMBF1c, a wheat (Triticum aestivum L.) Multiprotein Bridging Factor, confers heat tolerance in both yeast and rice.

Previously, we found an ethylene-responsive transcriptional co-activator, which was significantly induced by heat stress (HS) in both thermo-sensitive and thermo-tolerant wheat. The corresponding ORF was isolated from wheat, and named TaMBF1c (Multiprotein Bridging Factor1c). The deduced amino acid sequence revealed the presence of conserved MBF1 and helix-turn-helix domains at the N- and C-terminus, respectively, which were highly similar to rice ERTCA (Ethylene Response Transcriptional Co-Activator) and Arabidopsis MBF1c. The promoter region of TaMBF1c contained three heat shock elements (HSEs) and other stress-responsive elements. There was no detectable mRNA of TaMBF1c under control conditions, but the transcript was rapidly and significantly induced by heat stress not only at the seedling stage, but also at the flowering stage. It was also slightly induced by drought and H2O2 stresses, as well as by application of the ethylene synthesis precursor ACC, but not, however, by circadian rhythm, salt, ABA or MeJA treatments. Under normal temperatures, TaMBF1c-eGFP protein showed predominant nuclear localization with some levels of cytosol localization in the bombarded onion epidermal cells, but it was mainly detected in the nucleus with almost no eGFP signals in cytosol when the bombarded onion cells were cultured under high temperature conditions. Overexpression of TaMBF1c in yeast imparted tolerance to heat stress compared to cells expressing the vector alone. Most importantly, transgenic rice plants engineered to overexpress TaMBF1c showed higher thermotolerance than control plants at both seedling and reproductive stages. In addition, transcript levels of six Heat Shock Protein and two Trehalose Phosphate Synthase genes were higher in TaMBF1c transgenic lines than in wild-type rice upon heat treatment. Collectively, the present data suggest that TaMBF1c plays a pivotal role in plant thermotolerance and holds promising possibilities for improving heat tolerance in crops.

Arabidopsis HEAT SHOCK TRANSCRIPTION FACTORA1b overexpression enhances water productivity, resistance to drought, and infection

Heat-stressed crops suffer dehydration, depressed growth, and a consequent decline in water productivity, which is the yield of harvestable product as a function of lifetime water consumption and is a trait associated with plant growth and development. Heat shock transcription factor (HSF) genes have been implicated not only in thermotolerance but also in plant growth and development, and therefore could influence water productivity. Here it is demonstrated that Arabidopsis thaliana plants with increased HSFA1b expression showed increased water productivity and harvest index under water-replete and water-limiting conditions. In non-stressed HSFA1b-overexpressing (HSFA1bOx) plants, 509 genes showed altered expression, and these genes were not over-represented for development-associated genes but were for response to biotic stress. This confirmed an additional role for HSFA1b in maintaining basal disease resistance, which was stress hormone independent but involved H2O2 signalling. Fifty-five of the 509 genes harbour a variant of the heat shock element (HSE) in their promoters, here named HSE1b. Chromatin immunoprecipitation-PCR confirmed binding of HSFA1b to HSE1b in vivo, including in seven transcription factor genes. One of these is MULTIPROTEIN BRIDGING FACTOR1c (MBF1c). Plants overexpressing MBF1c showed enhanced basal resistance but not water productivity, thus partially phenocopying HSFA1bOx plants. A comparison of genes responsive to HSFA1b and MBF1c overexpression revealed a common group, none of which harbours a HSE1b motif. From this example, it is suggested that HSFA1b directly regulates 55 HSE1b-containing genes, which control the remaining 454 genes, collectively accounting for the stress defence and developmental phenotypes of HSFA1bOx.

Identification of the MBF1 heat-response regulon of Arabidopsis thaliana.

Brief periods of heat stress of even a few days can have a detrimental effect on yield production worldwide, causing devastating economic and societal impacts. Here we report on the identification of a new heat-response regulon in plants controlled by the multiprotein bridging factor 1c (MBF1c) protein of Arabidopsis thaliana. Members of the highly conserved MBF1 protein family function as non-DNA-binding transcriptional co-activators involved in regulating metabolic and development pathways in different organisms from yeast to humans. Nonetheless, our studies suggest that MBF1c from Arabidopsis functions as a transcriptional regulator which binds DNA and controls the expression of 36 different transcripts during heat stress, including the important transcriptional regulator DRE-binding protein 2A (DREB2A), two heat shock transcription factors (HSFs), and several zinc finger proteins. We further identify CTAGA as a putative response element for MBF1c, demonstrate that the DNA-binding domain of MBF1c has a dominant-negative effect on heat tolerance when constitutively expressed in plants, and show that constitutive expression of MBF1c in soybean enhances yield production in plants grown under controlled growth conditions without causing adverse effects on growth. Our findings could have a significant impact on improving heat tolerance and yield of different crops subjected to heat stress.

The Transcriptional Co-activator MBF1c Is a Key Regulator of Thermotolerance in Arabidopsis thaliana

The ability of an organism to acclimate to its environment is a key determinant in its global distribution and capacity to compete with other organisms. The heat stress response, a highly conserved environmental and developmental program in eukaryotic and prokaryotic organisms, is an important component of the acclimation response of plants. Previous studies have shown that heat shock transcription factors play an important role in thermotolerance in plants and other organisms, controlling the expression of different heat shock proteins and detoxifying enzymes. In contrast, although several other pathways, involving ethylene, salicylic acid (SA), and trehalose, were recently shown to play a central role in thermotolerance in plants, a key regulator of these responses was not identified. Here we report that the highly conserved transcriptional co-activator, MBF1c (multiprotein bridging factor 1c), is a key regulator of thermotolerance in Arabidopsis thaliana. MBF1c protein accumulates rapidly and is localized to nuclei during heat stress. MBF1c is required for thermotolerance and functions upstream to SA, trehalose, ethylene, and pathogenesis-related protein 1 during heat stress. In contrast, MBF1c is not required for the expression of transcripts encoding HSFA2 and different heat shock proteins. Interestingly, MBF1c interacts with TPS5 (trehalose phosphate synthase 5), which is also heat-inducible, and mutants deficient in TPS5 are thermosensitive. Our results provide evidence for the existence of a tightly coordinated heat stress-response network, involving trehalose-, SA-, and ethylene-signaling pathways, that is under the control of MBF1c.

Enhanced Tolerance to Environmental Stress in Transgenic Plants Expressing the Transcriptional Coactivator Multiprotein Bridging Factor 1c

Abiotic stresses cause extensive losses to agricultural production worldwide. Acclimation of plants to abiotic conditions such as drought, salinity, or heat is mediated by a complex network of transcription factors and other regulatory genes that control multiple defense enzymes, proteins, and pathways. Associated with the activity of different transcription factors are transcriptional coactivators that enhance their binding to the basal transcription machinery. Although the importance of stress-response transcription factors was demonstrated in transgenic plants, little is known about the function of transcriptional coactivators associated with abiotic stresses. Here, we report that constitutive expression of the stress-response transcriptional coactivator multiprotein bridging factor 1c (MBF1c) in Arabidopsis (Arabidopsis thaliana) enhances the tolerance of transgenic plants to bacterial infection, heat, and osmotic stress. Moreover, the enhanced tolerance of transgenic plants to osmotic and heat stress was maintained even when these two stresses were combined. The expression of MBF1c in transgenic plants augmented the accumulation of a number of defense transcripts in response to heat stress. Transcriptome profiling and inhibitor studies suggest that MBF1c expression enhances the tolerance of transgenic plants to heat and osmotic stress by partially activating, or perturbing, the ethylene-response signal transduction pathway. Present findings suggest that MBF1 proteins could be used to enhance the tolerance of plants to different abiotic stresses.