The AP2/ERF Transcription Factor TINY Modulates Brassinosteroid-Regulated Plant Growth and Drought Responses in Arabidopsis

Overexpression of PagLOL1b improves drought tolerance through increasing water use efficiency and reactive oxygen species scavenging in transgenic poplar

LESION SIMULATING DISEASE1 (LSD) family genes play a key role in plant response to abiotic and biotic stress. However, their functions in the resistance of tree to drought stress are still largely not clear. Here, five LSD family genes in poplar genome were identified. Phylogenetic and collinear relationship analysis showed that they belonged to LSD, LSD-one-like 1 (LOL1) and LSD-one-like 2 (LOL2) subfamilies, and experienced two segmental duplication events. PagLSDs were highly conserved in gene structure, and all PagLSDs contained at least two LSD domains. Expression pattern and cis-acting element analyses showed that PagLSDs were widely expressed in different organs, significantly induced by polyethylene glycol, and possessed a great number of plant growth, development, plant hormones, and biotic and abiotic stress elements in their promoter regions. Further physiological experiments with transgenic poplar plants revealed that overexpression of PagLOL1b significantly enhanced the drought tolerance of transgenic plants. The improved drought tolerance was closely associated with the significant increase in stomatal closure, water use efficiency, antioxidant enzyme gene expression and antioxidant enzyme activity in transgenic plants. The results in our study imply that PagLOL1b has great potential in the engineering of new tree varieties resistant to drought stress.

Surviving the stress: Understanding the molecular basis of plant adaptations and uncovering the role of mycorrhizal association in plant abiotic stresses

Environmental stresses severely impair plant growth, resulting in significant crop yield and quality loss. Among various abiotic factors, salt and drought stresses are one of the major factors that affect the nutrients and water uptake by the plants, hence ultimately various physiological aspects of the plants that compromises crop yield. Continuous efforts have been made to investigate, dissect and improve plant adaptations at the molecular level in response to drought and salinity stresses. In this context, the plant beneficial microbiome presents in the rhizosphere, endosphere, and phyllosphere, also referred as second genomes of the plant is well known for its roles in plant adaptations. Exploration of beneficial interaction of fungi with host plants known as mycorrhizal association is one such special interaction that can facilitates the host plants adaptations. Mycorrhiza assist in alleviating the salinity and drought stresses of plants via redistributing the ion imbalance through translocation to different parts of the plants, as well as triggering oxidative machinery. Mycorrhiza association also regulates the level of various plant growth regulators, osmolytes and assists in acquiring minerals that are helpful in plant's adaptation against extreme environmental stresses. The current review examines the role of various plant growth regulators and plants' antioxidative systems, followed by mycorrhizal association during drought and salt stresses.

The Potential Relevance of PnDREBs to Panax notoginseng Nitrogen Sensitiveness

The dehydration response element-binding (DREB) transcription factor is a subfamily of AP2/ERF. It actively responds to various abiotic stresses in plants. As one of the representative plants, Panax notoginseng is sensitive to Nitrogen (N). Here, bioinformatics analysis, the identification, chromosomal location, phylogeny, structure, cis-acting elements, and collinearity of PnDREBs were analyzed. In addition, the expression levels of PnDREBs were analyzed by quantitative reverse transcription PCR. In this study, 54 PnDREBs were identified and defined as PnDREB1 to PnDREB54. They were divided into 6 subfamilies (A1-A6). And 44 PnDREBs were irregularly distributed on 10 of 12 chromosomes. Each group showed specific motifs and exon-intron structures. By predicting cis-acting elements, the PnDREBs may participate in biotic stress, abiotic stress, and hormone induction. Collinear analysis showed that fragment duplication events were beneficial to the amplification and evolution of PnDREB members. The expression of PnDREBs showed obvious tissue specificity in its roots, flowers, and leaves. In addition, under the action of ammonium nitrogen and nitrate nitrogen at the 15 mM level, the level of PnDREB genes expression in roots varied to different degrees. In this study, we identified and characterized PnDREBs for the first time, and analyzed that PnDREBs may be related to the response of P. Notoginseng to N sensitiveness. The results of this study lay a foundation for further research on the function of PnDREBs in P. Notoginseng.

Time-Course Analysis and Transcriptomic Identification of a Group III ERF CmTINY2 Involved in Waterlogging Tolerance in Chrysanthemums × morifolium Ramat

'Hangju' is a variety of Chrysanthemum × morifolium Ramat. with both edible and medicinal value, cultivated as a traditional Chinese medicine for four centuries. The cultivation of 'Hangju' is currently at risk due to waterlogging, yet there is a lack of comprehensive understanding regarding its response to waterlogging stress. This study compared the waterlogging-tolerant 'Hangju' variety Enhanced Waterlogging Tolerance (EWT) with the waterlogging-sensitive variety CK ('zaoxiaoyangju'). EWT exhibited a more developed aeration tissue structure and demonstrated rapid growth regarding the adventitious roots following waterlogging. The time-course transcriptome analysis indicated that EWT could swiftly adjust the expression of the genes involved in the energy metabolism signaling pathways to acclimate to the waterlogged environment. Through WGCNA analysis, we identified Integrase-Type DNA-Binding Protein (CmTINY2) as a key factor in regulating the waterlogging tolerance in EWT. CmTINY2, a transcription factor belonging to the ethylene-responsive factor (ERF) subfamily III, operated within the nucleus and activated downstream gene expression. Its role in enhancing the waterlogging tolerance might be linked to the control of the stomatal aperture via the Ethylene-Responsive Element (ERE) gene. In summary, our research elucidated that the waterlogging tolerance displayed by EWT is a result of a combination of the morphological structure and molecular regulatory mechanisms. Furthermore, the study of the functions of CmTINY2 from ERF subfamily III also broadened our knowledge of the role of the ERF genes in the waterlogging signaling pathways.

Monosaccharide transporter OsMST6 is activated by transcription factor OsERF120 to enhance chilling tolerance in rice seedlings

Chilling stress caused by extreme weather is threatening global rice (Oryza sativa L.) production. Identifying components of the signal transduction pathways underlying chilling tolerance in rice would advance molecular breeding. Here, we report that OsMST6, which encodes a monosaccharide transporter, positively regulates the chilling tolerance of rice seedlings. mst6 mutants showed hypersensitivity to chilling, while OsMST6 overexpression lines were tolerant. During chilling stress, OsMST6 transported more glucose into cells to modulate sugar and abscisic acid signaling pathways. We showed that the transcription factor OsERF120 could bind to the DRE/CRT element of the OsMST6 promoter and activate the expression of OsMST6 to positively regulate chilling tolerance. Genetically, OsERF120 was functionally dependent on OsMST6 when promoting chilling tolerance. In summary, OsERF120 and OsMST6 form a new downstream chilling regulatory pathway in rice in response to chilling stress, providing valuable findings for molecular breeding aimed at achieving global food security.

The BTB-BACK-TAZ domain protein MdBT2 reduces drought resistance by weakening the positive regulatory effect of MdHDZ27 on apple drought tolerance via ubiquitination

Drought stress is one of the dominating challenges to the growth and productivity in crop plants. Elucidating the molecular mechanisms of plants responses to drought stress is fundamental to improve fruit quality. However, such molecular mechanisms are poorly understood in apple (Malus domestica Borkh.). In this study, we explored that the BTB-BACK-TAZ protein, MdBT2, negatively modulates the drought tolerance of apple plantlets. Moreover, we identified a novel Homeodomain-leucine zipper (HD-Zip) transcription factor, MdHDZ27, using a yeast two-hybrid (Y2H) screen with MdBT2 as the bait. Overexpression of MdHDZ27 in apple plantlets, calli, and tomato plantlets enhanced their drought tolerance by promoting the expression of drought tolerance-related genes [responsive to dehydration 29A (MdRD29A) and MdRD29B]. Biochemical analyses demonstrated that MdHDZ27 directly binds to and activates the promoters of MdRD29A and MdRD29B. Furthermore, in vitro and in vivo assays indicate that MdBT2 interacts with and ubiquitinates MdHDZ27, via the ubiquitin/26S proteasome pathway. This ubiquitination results in the degradation of MdHDZ27 and weakens the transcriptional activation of MdHDZ27 on MdRD29A and MdRD29B. Finally, a series of transgenic analyses in apple plantlets further clarified the role of the relationship between MdBT2 and MdHDZ27, as well as the effect of their interaction on drought resistance in apple plantlets. Collectively, our findings reveal a novel mechanism by which the MdBT2-MdHDZ27 regulatory module controls drought tolerance, which is of great significance for enhancing the drought resistance of apple and other plants.

TaGSK3 regulates wheat development and stress adaptation through BR-dependent and BR-independent pathways

The GSK3/SHAGGY-like kinase plays critical roles in plant development and response to stress, but its specific function remains largely unknown in wheat (Triticum aestivum L.). In this study, we investigated the function of TaGSK3, a GSK3/SHAGGY-like kinase, in wheat development and response to stress. Our findings demonstrated that TaGSK3 mutants had significant effects on wheat seedling development and brassinosteroid (BR) signalling. Quadruple and quintuple mutants showed amplified BR signalling, promoting seedling development, while a sextuple mutant displayed severe developmental defects but still responded to exogenous BR signals, indicating redundancy and non-BR-related functions of TaGSK3. A gain-of-function mutation in TaGSK3-3D disrupted BR signalling, resulting in compact and dwarf plant architecture. Notably, this mutation conferred significant drought and heat stress resistance of wheat, and enhanced heat tolerance independent of BR signalling, unlike knock-down mutants. Further research revealed that this mutation maintains a higher relative water content by regulating stomatal-mediated water loss and maintains a lower ROS level to reduces cell damage, enabling better growth under stress. Our study provides comprehensive insights into the role of TaGSK3 in wheat development, stress response, and BR signal transduction, offering potential for modifying TaGSK3 to improve agronomic traits and enhance stress resistance in wheat.

BRZ-INSENSITIVE-LONG HYPOCOTYL8 inhibits kinase-mediated phosphorylation to regulate brassinosteroid signaling

Glycogen synthase kinase 3 (GSK3) is an evolutionarily conserved serine/threonine protein kinase in eukaryotes. In plants, the GSK3-like kinase BRASSINOSTEROID-INSENSITIVE 2 (BIN2) functions as a central signaling node through which hormonal and environmental signals are integrated to regulate plant development and stress adaptation. BIN2 plays a major regulatory role in brassinosteroid (BR) signaling and is critical for phosphorylating/inactivating BRASSINAZOLE-RESISTANT 1 (BZR1), also known as BRZ-INSENSITIVE-LONG HYPOCOTYL 1 (BIL1), a master transcription factor of BR signaling, but the detailed regulatory mechanism of BIN2 action has not been fully revealed. In this study, we identified BIL8 as a positive regulator of BR signaling and plant growth in Arabidopsis (Arabidopsis thaliana). Genetic and biochemical analyses showed that BIL8 is downstream of the BR receptor BRASSINOSTEROID-INSENSITIVE 1 (BRI1) and promotes the dephosphorylation of BIL1/BZR1. BIL8 interacts with and inhibits the activity of the BIN2 kinase, leading to the accumulation of dephosphorylated BIL1/BZR1. BIL8 suppresses the cytoplasmic localization of BIL1/BZR1, which is induced via BIN2-mediated phosphorylation. Our study reveals a regulatory factor, BIL8, that positively regulates BR signaling by inhibiting BIN2 activity.

Interaction of the Transcription Factors BES1/BZR1 in Plant Growth and Stress Response

Bri1-EMS Suppressor 1 (BES1) and Brassinazole Resistant 1 (BZR1) are two key transcription factors in the brassinosteroid (BR) signaling pathway, serving as crucial integrators that connect various signaling pathways in plants. Extensive genetic and biochemical studies have revealed that BES1 and BZR1, along with other protein factors, form a complex interaction network that governs plant growth, development, and stress tolerance. Among the interactome of BES1 and BZR1, several proteins involved in posttranslational modifications play a key role in modifying the stability, abundance, and transcriptional activity of BES1 and BZR1. This review specifically focuses on the functions and regulatory mechanisms of BES1 and BZR1 protein interactors that are not involved in the posttranslational modifications but are crucial in specific growth and development stages and stress responses. By highlighting the significance of the BZR1 and BES1 interactome, this review sheds light on how it optimizes plant growth, development, and stress responses.

Revealing critical mechanisms in determining sorghum resistance to drought and salt using mRNA, small RNA and degradome sequencing

BACKGROUND

Plant growth and development are severely threatened by drought and salt stresses. Compared with structural genes, transcription factors (TFs) play more pivotal roles in plant growth and stress adaptation. However, the underlying mechanisms of sorghum adapting to drought and salt are insufficient, and systematic analysis of TFs in response to the above stresses is lacking.

RESULTS

In this study, TFs were identified in sorghum and model plants (Arabidopsis thaliana and rice), and gene number and conserved domain were compared between sorghum and model plants. According to syntenic analysis, the expansion of sorghum and rice TFs may be due to whole-genome duplications. Between sorghum and model plants TFs, specific conserved domains were identified and they may be related to functional diversification of TFs. Forty-five key genes in sorghum, including four TFs, were likely responsible for drought adaption based on differently expression analysis. MiR5072 and its target gene (Sobic.001G449600) may refer to the determination of sorghum drought resistance according to small RNA and degradome analysis. Six genes were associated with drought adaptation of sorghum based on weighted gene co-expression network analysis (WGCNA). Similarly, the core genes in response to salt were also characterized using the above methods. Finally, 15 candidate genes, particularly two TFs (Sobic.004G300300, HD-ZIP; Sobic.003G244100, bZIP), involved in combined drought and salt resistance of sorghum were identified.

CONCLUSIONS

In summary, the findings in this study help clarify the molecular mechanisms of sorghum responding to drought and salt. We identified candidate genes and provide important genetic resource for potential development of drought-tolerant and salt-tolerant sorghum plants.

VvERF117 positively regulates grape cold tolerance through direct regulation of the antioxidative gene BAS1

Cold stress significantly threatens grape quality, yield, and geographical distribution. Although ethylene-responsive factors (ERFs) are recognized for their pivotal roles in cold stress, the regulatory mechanisms of many ERFs contributing to tolerance remain unclear. In this study, we identified the cold-responsive gene VvERF117 and elucidated its positive regulatory function in cold tolerance. VvERF117 exhibits transcriptional activity and localizes to the nucleus. VvERF117 overexpression improved cold tolerance in transgenic Arabidopsis, grape calli, and grape leaves, whereas VvERF117 silencing increased cold sensitivity in grape calli and leaves. Furthermore, VvERF117 overexpression remarkably upregulated the expression of several stress-related genes. Importantly, BAS1, encoding a 2-Cys peroxidase (POD), was confirmed as a direct target gene of VvERF117. Meanwhile, compared to the wild-type, POD activity and H2O2 content were remarkably increased and decreased in VvERF117-overexpressing grape calli and leaves, respectively. Conversely, VvERF117 silencing displayed the opposite trend in grape calli and leaves under cold stress. These findings indicate that VvERF117 plays a positive role in cold resistance by, at least in part, enhancing antioxidant capacity through regulating the POD-encoding gene VvBAS1, leading to effective mitigation of reactive oxygen species.

The CsAP2-09-CsWRKY25-CsRBOH2 cascade confers resistance against citrus bacterial canker by regulating ROS homeostasis

Citrus bacterial canker (CBC) is a serious bacterial disease caused by Xanthomonas citri subsp. citri (Xcc) that adversely impacts the global citrus industry. In a previous study, we demonstrated that overexpression of an Xcc-inducible apetala 2/ethylene response factor encoded by Citrus sinensis, CsAP2-09, enhances CBC resistance. The mechanism responsible for this effect, however, is not known. In the present study, we showed that CsAP2-09 targeted the promoter of the Xcc-inducible WRKY transcription factor coding gene CsWRKY25 directly, activating its transcription. CsWRKY25 was found to localize to the nucleus and to activate transcriptional activity. Plants overexpressing CsWRKY25 were more resistant to CBC and showed higher expression of the respiratory burst oxidase homolog (RBOH) CsRBOH2, in addition to exhibiting increased RBOH activity. Transient overexpression assays in citrus confirmed that CsWRKY25 and CsRBOH2 participated in the generation of reactive oxygen species (ROS) bursts, which were able to restore the ROS degradation caused by CsAP2-09 knockdown. Moreover, CsWRKY25 was found to bind directly to W-box elements within the CsRBOH2 promoter. Notably, CsRBOH2 knockdown had been reported previously to reduce the CBC resistance, while demonstrated in this study, CsRBOH2 transient overexpression can enhance the CBC resistance. Overall, our results outline a pathway through which CsAP2-09-CsWRKY25 transcriptionally reprograms CsRBOH2-mediated ROS homeostasis in a manner conducive to CBC resistance. These data offer new insight into the mechanisms and regulatory pathways through which CsAP2-09 regulates CBC resistance, highlighting its potential utility as a target for the breeding of CBC-resistant citrus varieties.

Exogenous 24-Epibrassinolide Enhanced Drought Tolerance and Promoted BRASSINOSTEROID-INSENSITIVE2 Expression of Quinoa

Brassinosteroids (BRs) are involved in the regulation of biotic and abiotic stresses in plants. The molecular mechanisms of BRs that alleviate the drought stress in quinoa have rarely been reported. Here, quinoa seedlings were treated with 24-epibrassinolide (EBR) and we transiently transferred CqBIN2 to the quinoa seedlings' leaves using VIGS technology to analyze the molecular mechanism of the BR mitigation drought stress. The results showed that EBR treatment significantly increased the root growth parameters, the antioxidant enzyme activities, and the osmolyte content, resulting in a decrease in the H2O2, O2∙-, and malondialdehyde content in quinoa. A transcriptome analysis identified 8124, 2761, and 5448 differentially expressed genes (DEGs) among CK and Drought, CK and EBR + Drought, and Drought and EBR + Drought groups. WGCNA divided these DEGs into 19 modules in which these characterized genes collectively contributed significantly to drought stress. In addition, the EBR application also up-regulated the transcript levels of CqBIN2 and proline biosynthesis genes. Silenced CqBIN2 by VIGS could reduce the drought tolerance, survival rate, and proline content in quinoa seedlings. These findings not only revealed that exogenous BRs enhance drought tolerance, but also provided insight into the novel functions of CqBIN2 involved in regulating drought tolerance in plants.

Recent Advances in the Crosstalk between Brassinosteroids and Environmental Stimuli

Due to their sessile lifestyle, plants need to optimize their growth in order to adapt to ever-changing environments. Plants receive stimuli from the environment and convert them into cellular responses. Brassinosteroids (BRs), as growth-promoting steroid hormones, play a significant role in the tradeoff between growth and environmental responses. Here, we provide a comprehensive summary for understanding the crosstalk between BR and various environmental stresses, including water availability, temperature fluctuations, salinization, nutrient deficiencies and diseases. We also highlight the bottlenecks that need to be addressed in future studies. Ultimately, we suppose to improve plant environmental adaptability and crop yield by excavating natural BR mutants or modifying BR signaling and its targets.

SNAC1-OsERF103-OsSDG705 module mediates drought response in rice

Drought stress profoundly hampers both plant growth and crop yield. To combat this, plants have evolved intricate transcriptional regulation mechanisms as a pivotal strategy. Through a genetic screening with rice genome-scale mutagenesis pool under drought stress, we identified an APETALA2/Ethylene Responsive Factor, namely OsERF103, positively responds to drought tolerance in rice. Combining chromatin immunoprecipitation sequencing and RNA sequencing analyses, we pinpointed c. 1000 genes directly influenced by OsERF103. Further results revealed that OsERF103 interacts with Stress-responsive NAC1 (SNAC1), a positive regulator of drought tolerance in rice, to synergistically regulate the expression of key drought-related genes, such as OsbZIP23. Moreover, we found that OsERF103 recruits a Su(var)3-9,enhancer of zeste and trithorax-domain group protein 705, which encodes a histone 3 lysine 4 (H3K4)-specific methyltransferase to specifically affect the deposition of H3K4me3 at loci like OsbZIP23 and other genes linked to dehydration responses. Additionally, the natural alleles of OsERF103 are selected during the domestication of both indica and japonica rice varieties and exhibit significant geographic distribution. Collectively, our findings have unfurled a comprehensive mechanistic framework underlying the OsERF103-mediated cascade regulation of drought response. This discovery not only enhances our understanding of drought signaling but also presents a promising avenue for the genetic improvement of drought-tolerant rice cultivars.

Comprehensive investigation of BZR gene family in four dicots and the function of PtBZR9 and PtBZR12 under drought stress

Brassinazole-resistant (BZR) transcription factor plays an important role in plant growth and stress resistance through brassinosteroid (BR) signal transduction. However, systematic analysis of the BZR family in dicots remains limited. In this study, we conducted a genome-wide study of four typical dicots: Arabidopsis thaliana, Carica papaya, Vitis vinifera and Populus trichocarpa. Thirty-four BZR gene family members were identified and classified them into three subfamilies. Analysis of promoter and expression patterns revealed crucial role of a pair of homologous BZR genes, PtBZR9 and PtBZR12, in poplar may play a critical role under abiotic stress. PtBZR9 and PtBZR12 were localised in the nucleus and exhibited mutual interactions. Moreover, transient overexpression (OE) of PtBZR9 and PtBZR12 in poplar enhanced tolerance to drought stress. The phenotypic and physiological characteristics of PtBZR9 and PtBZR12 OE in Arabidopsis mirrored those of transient OE in the poplar. Additionally, PtBZR9 and PtBZR12 can bind to the E-box element. Under exogenous BR treatment, transgenic lines displayed a greater decrease in root length than the wild type. Thus, these findings provide a solid foundation for future research on the complex regulatory mechanisms of BZR genes.

APETALA2/ethylene-responsive factors in higher plant and their roles in regulation of plant stress response

Plants, anchored throughout their life cycles, face a unique set of challenges from fluctuating environments and pathogenic assaults. Central to their adaptative mechanisms are transcription factors (TFs), particularly the AP2/ERF superfamily-one of the most extensive TF families unique to plants. This family plays instrumental roles in orchestrating diverse biological processes ranging from growth and development to secondary metabolism, and notably, responses to both biotic and abiotic stresses. Distinguished by the presence of the signature AP2 domain or its responsiveness to ethylene signals, the AP2/ERF superfamily has become a nexus of research focus, with increasing literature elucidating its multifaceted roles. This review provides a synoptic overview of the latest research advancements on the AP2/ERF family, spanning its taxonomy, structural nuances, prevalence in higher plants, transcriptional and post-transcriptional dynamics, and the intricate interplay in DNA-binding and target gene regulation. Special attention is accorded to the ethylene response factor B3 subgroup protein Pti5 and its role in stress response, with speculative insights into its functionalities and interaction matrix in tomatoes. The overarching goal is to pave the way for harnessing these TFs in the realms of plant genetic enhancement and novel germplasm development.

Genome-wide analysis and expression pattern of the ZoPP2C gene family in Zingiber officinale Roscoe

BACKGROUND

Protein phosphatases type 2C (PP2C) are heavily involved in plant growth and development, hormone-related signaling pathways and the response of various biotic and abiotic stresses. However, a comprehensive report identifying the genome-scale of PP2C gene family in ginger is yet to be published.

RESULTS

In this study, 97 ZoPP2C genes were identified based on the ginger genome. These genes were classified into 15 branches (A-O) according to the phylogenetic analysis and distributed unevenly on 11 ginger chromosomes. The proteins mainly functioned in the nucleus. Similar motif patterns and exon/intron arrangement structures were identified in the same subfamily of ZoPP2Cs. Collinearity analysis indicated that ZoPP2Cs had 33 pairs of fragment duplicated events uniformly distributed on the corresponding chromosomes. Furthermore, ZoPP2Cs showed greater evolutionary proximity to banana's PP2Cs. The forecast of cis-regulatory elements and transcription factor binding sites demonstrated that ZoPP2Cs participate in ginger growth, development, and responses to hormones and stresses. ZoERFs have plenty of binding sites of ZoPP2Cs, suggesting a potential synergistic contribution between ZoERFs and ZoPP2Cs towards regulating growth/development and adverse conditions. The protein-protein interaction network displayed that five ZoPP2Cs (9/23/26/49/92) proteins have robust interaction relationship and potential function as hub proteins. Furthermore, the RNA-Seq and qRT-PCR analyses have shown that ZoPP2Cs exhibit various expression patterns during ginger maturation and responses to environmental stresses such as chilling, drought, flooding, salt, and Fusarium solani. Notably, exogenous application of melatonin led to notable up-regulation of ZoPP2Cs (17/59/11/72/43) under chilling stress.

CONCLUSIONS

Taken together, our investigation provides significant insights of the ginger PP2C gene family and establishes the groundwork for its functional validation and genetic engineering applications.

Characterization of Almond Scion/Rootstock Communication in Cultivar and Rootstock Tissues through an RNA-Seq Approach

The rootstock genotype plays a crucial role in determining various aspects of scion development, including the scion three-dimensional structure, or tree architecture. Consequently, rootstock choice is a pivotal factor in the establishment of new almond (Prunus amygdalus (L.) Batsch, syn P. dulcis (Mill.)) intensive planting systems, demanding cultivars that can adapt to distinct requirements of vigor and shape. Nevertheless, considering the capacity of the rootstock genotype to influence scion development, it is likely that the scion genotype reciprocally affects rootstock performance. In the context of this study, we conducted a transcriptomic analysis of the scion/rootstock interaction in young almond trees, with a specific focus on elucidating the scion impact on the rootstock molecular response. Two commercial almond cultivars were grafted onto two hybrid rootstocks, thereby generating four distinct combinations. Through RNA-Seq analysis, we discerned that indeed, the scion genotype exerts an influence on the rootstock expression profile. This influence manifests through the modulation of genes associated with hormonal regulation, cell division, root development, and light signaling. This intricate interplay between scion and rootstock communication plays a pivotal role in the development of both scion and rootstock, underscoring the critical importance of a correct choice when establishing new almond orchards.

Inhibition of the maize salt overly sensitive pathway by ZmSK3 and ZmSK4

Soil salinity is a worldwide problem that adversely affects plant growth and crop productivity. The salt overly sensitive (SOS) pathway is evolutionarily conserved and essential for plant salt tolerance. In this study, we reveal how the maize shaggy/glycogen synthase kinase 3-like kinases ZmSK3 and ZmSK4, orthologs of brassinosteroid insensitive 2 in Arabidopsis thaliana, regulate the maize SOS pathway. ZmSK3 and ZmSK4 interact with and phosphorylate ZmSOS2, a core member of the maize SOS pathway. The mutants defective in ZmSK3 or ZmSK4 are hyposensitive to salt stress, with higher salt-induced activity of ZmSOS2 than that in the wild type. Furthermore, the Ca2+ sensors ZmSOS3 and ZmSOS3-like calcium binding protein 8 (ZmSCaBP8) activate ZmSOS2 to maintain Na+/K+ homeostasis under salt stress and may participate in the regulation of ZmSOS2 by ZmSK3 and ZmSK4. These findings discover the regulation of the maize SOS pathway and provide important gene targets for breeding salt-tolerant maize.

The AP2/ERF transcription factor PtoERF15 confers drought tolerance via JA-mediated signaling in Populus

Drought stress is one of the major limiting factors for the growth and development of perennial trees. Xylem vessels act as the center of water conduction in woody species, but the underlying mechanism of its development and morphogenesis under water-deficient conditions remains elucidation. Here, we identified and characterized an osmotic stress-induced ETHYLENE RESPONSE FACTOR 15 (PtoERF15) and its target, PtoMYC2b, which was involved in mediating vessel size, density, and cell wall thickness in response to drought in Populus tomentosa. PtoERF15 is preferentially expressed in differentiating xylem of poplar stems. Overexpression of PtoERF15 contributed to stem water potential maintaining, thus promoting drought tolerance. RNA-Seq and biochemical analysis further revealed that PtoERF15 directly regulated PtoMYC2b, encoding a switch of JA signaling pathway. Additionally, our findings verify that three sets of homologous genes from NAC (NAM, ATAF1/2, and CUC2) gene family: PtoSND1-A1/A2, PtoVND7-1/7-2, and PtoNAC118/120, as the targets of PtoMYC2b, are involved in the regulation of vessel morphology in poplar. Collectively, our study provides molecular evidence for the involvement of the PtoERF15-PtoMYC2b transcription cascade in maintaining stem water potential through the regulation of xylem vessel development, ultimately improving drought tolerance in poplar.

HbBIN2 Functions in Plant Cold Stress Resistance through Modulation of HbICE1 Transcriptional Activity and ROS Homeostasis in Hevea brasiliensis

Cold stress poses significant limitations on the growth, latex yield, and ecological distribution of rubber trees (Hevea brasiliensis). The GSK3-like kinase plays a significant role in helping plants adapt to different biotic and abiotic stresses. However, the functions of GSK3-like kinase BR-INSENSITIVE 2 (BIN2) in Hevea brasiliensis remain elusive. Here, we identified HbBIN2s of Hevea brasiliensis and deciphered their roles in cold stress resistance. The transcript levels of HbBIN2s are upregulated by cold stress. In addition, HbBIN2s are present in both the nucleus and cytoplasm and have the ability to interact with the INDUCER OF CBF EXPRESSION1(HbICE1) transcription factor, a central component in cold signaling. HbBIN2 overexpression in Arabidopsis displays decreased tolerance to chilling stress with a lower survival rate and proline content but a higher level of electrolyte leakage (EL) and malondialdehyde (MDA) than wild type under cold stress. Meanwhile, HbBIN2 transgenic Arabidopsis treated with cold stress exhibits a significant increase in the accumulation of reactive oxygen species (ROS) and a decrease in the activity of antioxidant enzymes. Further investigation reveals that HbBIN2 inhibits the transcriptional activity of HbICE1, thereby attenuating the expression of C-REPEAT BINDING FACTOR (HbCBF1). Consistent with this, overexpression of HbBIN2 represses the expression of CBF pathway cold-regulated genes under cold stress. In conclusion, our findings indicate that HbBIN2 functions as a suppressor of cold stress resistance by modulating HbICE1 transcriptional activity and ROS homeostasis.

BRASSINOSTEROID-INSENSITIVE 2 regulates salt stress tolerance in Arabidopsis by promoting AGL16 activity

Salt stress is a negative environmental factors to affecting plants. Salinity inhibits seed germination and root growth, which reduces the biomass of agricultural plants. BRASSINOSTEROID-INSENSITIVE2 (BIN2) functions as a signalling hub to integrate the perception and transduction of plant growth and stress tolerance by the phosphorylation of target proteins. However, only a small number of target molecules have been discovered thus far. In this study, we present evidence that BIN2 controls the post-transcriptional activity of AGL16. BIN2 interacts and phosphorylates AGL16, which increases AGL16 stability and transcriptional activity. Genetic testing showed that the agl16 mutant can restore the reduction in the seed germination rate and primary root growth of the bin2-1 mutant, while the overexpression of AGL16 in the bin2-3bil1bil2 mutant reduced the salt tolerance compared with bin2-3bil1bil2 in response to salt stress. Taken together, our data identify a BIN2-AGL16 core protein module that is mediates the inhibition of seed germination and primary root growth under salt stress.

The DREB transcription factor, a biomacromolecule, responds to abiotic stress by regulating the expression of stress-related genes

Abiotic stress is a crucial factor that affects plant survival and growth and even leads to plant death in severe cases. Transcription factors can enhance the ability of plants to fight against various stresses by controlling the expression of downstream genes. The dehydration response element binding protein (DREB) is the most extensive subfamily of AP2/ERF transcription factors involved in abiotic stress. However, insufficient research on the signal network of DREB transcription factors has limited plant growth and reproduction. Furthermore, field planting of DREB transcription factors and their roles under multiple stress also require extensive research. Previous reports on DREB transcription factors have focused on the regulation of DREB expression and its roles in plant abiotic stress. In recent years, there has been new progress in DREB transcription factors. Here, the structure and classification, evolution and regulation, role in abiotic stress, and application in crops of DREB transcription factors were reviewed. And this paper highlighted the evolution of DREB1/CBF, as well as the regulation of DREB transcription factors under the participation of plant hormone signals and the roles of subgroups in abiotic stress. In the future, it will lay a solid foundation for further study of DREB transcription factors and pave the way for the cultivation of resistant plants.

An intrinsically disordered region-containing protein mitigates the drought-growth trade-off to boost yields

Drought stress poses a serious threat to global agricultural productivity and food security. Plant resistance to drought is typically accompanied by a growth deficit and yield penalty. Herein, we report a previously uncharacterized, dicotyledon-specific gene, Stress and Growth Interconnector (SGI), that promotes growth during drought in the oil crop rapeseed (Brassica napus) and the model plant Arabidopsis (Arabidopsis thaliana). Overexpression of SGI conferred enhanced biomass and yield under water-deficient conditions, whereas corresponding CRISPR SGI mutants exhibited the opposite effects. These attributes were achieved by mediating reactive oxygen species (ROS) homeostasis while maintaining photosynthetic efficiency to increase plant fitness under water-limiting environments. Further spatial-temporal transcriptome profiling revealed dynamic reprogramming of pathways for photosynthesis and stress responses during drought and the subsequent recovery. Mechanistically, SGI represents an intrinsically disordered region-containing protein that interacts with itself, catalase isoforms, dehydrins, and other drought-responsive positive factors, restraining ROS generation. These multifaceted interactions stabilize catalases in response to drought and facilitate their ROS-scavenging activities. Taken altogether, these findings provide insights into currently underexplored mechanisms to circumvent trade-offs between plant growth and stress tolerance that will inform strategies to breed climate-resilient, higher yielding crops for sustainable agriculture.

Maize Transcription Factor ZmHsf28 Positively Regulates Plant Drought Tolerance

Identification of central genes governing plant drought tolerance is fundamental to molecular breeding and crop improvement. Here, maize transcription factor ZmHsf28 is identified as a positive regulator of plant drought responses. ZmHsf28 exhibited inducible gene expression in response to drought and other abiotic stresses. Overexpression of ZmHsf28 diminished drought effects in Arabidopsis and maize. Gene silencing of ZmHsf28 via the technology of virus-induced gene silencing (VIGS) impaired maize drought tolerance. Overexpression of ZmHsf28 increased jasmonate (JA) and abscisic acid (ABA) production in transgenic maize and Arabidopsis by more than two times compared to wild-type plants under drought conditions, while it decreased reactive oxygen species (ROS) accumulation and elevated stomatal sensitivity significantly. Transcriptomic analysis revealed extensive gene regulation by ZmHsf28 with upregulation of JA and ABA biosynthesis genes, ROS scavenging genes, and other drought related genes. ABA treatment promoted ZmHsf28 regulation of downstream target genes. Specifically, electrophoretic mobility shift assays (EMSA) and yeast one-hybrid (Y1H) assay indicated that ZmHsf28 directly bound to the target gene promoters to regulate their gene expression. Taken together, our work provided new and solid evidence that ZmHsf28 improves drought tolerance both in the monocot maize and the dicot Arabidopsis through the implication of JA and ABA signaling and other signaling pathways, shedding light on molecular breeding for drought tolerance in maize and other crops.

HD-ZIP Transcription Factors and Brassinosteroid Signaling Play a Role in Capitulum Patterning in Chrysanthemum

Chrysanthemum is a genus in the Asteraceae family containing numerous cut flower varieties with high ornamental value. It owes its beauty to the composite flower head, which resembles a compact inflorescence. This structure is also known as a capitulum, in which many ray and disc florets are densely packed. The ray florets are localized at the rim, are male sterile, and have large colorful petals. The centrally localized disc florets develop only a small petal tube but produce fertile stamens and a functional pistil. Nowadays, varieties with more ray florets are bred because of their high ornamental value, but, unfortunately, this is at the expense of their seed setting. In this study, we confirmed that the disc:ray floret ratio is highly correlated to seed set efficiency, and therefore, we further investigated the mechanisms that underlie the regulation of the disc:ray floret ratio. To this end, a comprehensive transcriptomics analysis was performed in two acquired mutants with a higher disc:ray floret ratio. Among the differentially regulated genes, various potential brassinosteroid (BR) signaling genes and HD-ZIP class IV homeodomain transcription factors stood out. Detailed follow-up functional studies confirmed that reduced BR levels and downregulation of HD-ZIP IV gene Chrysanthemum morifolium PROTODERMAL FACTOR 2 (CmPDF2) result in an increased disc:ray floret ratio, thereby providing ways to improve seed set in decorative chrysanthemum varieties in the future.

Brassinosteroid gene regulatory networks at cellular resolution in the Arabidopsis root

Brassinosteroids are plant steroid hormones that regulate diverse processes, such as cell division and cell elongation, through gene regulatory networks that vary in space and time. By using time series single-cell RNA sequencing to profile brassinosteroid-responsive gene expression specific to different cell types and developmental stages of the Arabidopsis root, we identified the elongating cortex as a site where brassinosteroids trigger a shift from proliferation to elongation associated with increased expression of cell wall-related genes. Our analysis revealed HOMEOBOX FROM ARABIDOPSIS THALIANA 7 (HAT7) and GT-2-LIKE 1 (GTL1) as brassinosteroid-responsive transcription factors that regulate cortex cell elongation. These results establish the cortex as a site of brassinosteroid-mediated growth and unveil a brassinosteroid signaling network regulating the transition from proliferation to elongation, which illuminates aspects of spatiotemporal hormone responses.

Regulation of the regulators: Transcription factors controlling biosynthesis of plant secondary metabolites during biotic stresses and their regulation by miRNAs

Biotic stresses threaten to destabilize global food security and cause major losses to crop yield worldwide. In response to pest and pathogen attacks, plants trigger many adaptive cellular, morphological, physiological, and metabolic changes. One of the crucial stress-induced adaptive responses is the synthesis and accumulation of plant secondary metabolites (PSMs). PSMs mitigate the adverse effects of stress by maintaining the normal physiological and metabolic functioning of the plants, thereby providing stress tolerance. This differential production of PSMs is tightly orchestrated by master regulatory elements, Transcription factors (TFs) express differentially or undergo transcriptional and translational modifications during stress conditions and influence the production of PSMs. Amongst others, microRNAs, a class of small, non-coding RNA molecules that regulate gene expression post-transcriptionally, also play a vital role in controlling the expression of many such TFs. The present review summarizes the role of stress-inducible TFs in synthesizing and accumulating secondary metabolites and also highlights how miRNAs fine-tune the differential expression of various stress-responsive transcription factors during biotic stress.

Regulatory network of GSK3-like kinases and their role in plant stress response

Glycogen synthase kinase 3 (GSK3) family members are evolutionally conserved Ser/Thr protein kinases in mammals and plants. In plants, the GSK3s function as signaling hubs to integrate the perception and transduction of diverse signals required for plant development. Despite their role in the regulation of plant growth and development, emerging research has shed light on their multilayer function in plant stress responses. Here we review recent advances in the regulatory network of GSK3s and the involvement of GSK3s in plant adaptation to various abiotic and biotic stresses. We also discuss the molecular mechanisms underlying how plants cope with environmental stresses through GSK3s-hormones crosstalk, a pivotal biochemical pathway in plant stress responses. We believe that our overview of the versatile physiological functions of GSK3s and underlined molecular mechanism of GSK3s in plant stress response will not only opens further research on this important topic but also provide opportunities for developing stress-resilient crops through the use of genetic engineering technology.

CsAP2-09 confers resistance against citrus bacterial canker by regulating CsGH3.1L-mediated phytohormone biosynthesis

Citrus bacterial canker (CBC) is a serious bacterial disease affecting citrus plantations and the citrus industry all over the world. We have previously shown that an apetala 2/ethylene response factor in Citrus sinensis, CsAP2-09, positively regulated resistance to CBC, although the regulatory mechanisms remained undetermined. Here, we demonstrated that CsAP2-09 positively and sustainably controlled resistance to CBC in three-year transgenic plants. CsAP2-09 was found to be a transcriptional activator, and qRT-PCR and dual luciferase assays showed that it controlled the expression CsGH3.1L. CsAP2-09 bound directly to the promotor of CsGH3.1L, shown by yeast one-hybrid assay, with the binding site confirmed by electrophoretic mobility shift assay. Biochemical assays showed that CsAP2-09 negatively regulated the biosynthesis of indole acetic acid (IAA) and positively regulated that of salicylic acid (SA) and ethylene, verified with transient overexpression of CsGH3.1L. The combination of these results with those of previous reports indicated that SA, ethylene, and IAA can directly regulate CBC resistance. Overall, we revealed a pathway whereby CsAP2-09 conferred CBC resistance by direct binding to the CsGH3.1L promoter, activating its expression and modulating IAA, SA, and ethylene biosynthesis. Our study indicates the potential value of manipulating CsAP2-09 and CsGH3.1L in the breeding of CBC-resistant citrus.

Genome-Wide Identification of the ERF Transcription Factor Family for Structure Analysis, Expression Pattern, and Response to Drought Stress in Populus alba × Populus glandulosa

The Ethylene Responsive Factor (ERF) transcription factor family is important for regulating plant growth and stress responses. Although the expression patterns of ERF family members have been reported in many plant species, their role in Populus alba × Populus glandulosa, an important model plant for forest research, remains unclear. In this study, we identified 209 PagERF transcription factors by analyzing the P. alba × P. glandulosa genome. We analyzed their amino acid sequences, molecular weight, theoretical pI (Isoelectric point), instability index, aliphatic index, grand average of hydropathicity, and subcellular localization. Most PagERFs were predicted to localize in the nucleus, with only a few PagERFs localized in the cytoplasm and nucleus. Phylogenetic analysis divided the PagERF proteins into ten groups, Class I to X, with those belonging to the same group containing similar motifs. Cis-acting elements associated with plant hormones, abiotic stress responses, and MYB binding sites were analyzed in the promoters of PagERF genes. We used transcriptome data to analyze the expression patterns of PagERF genes in different tissues of P. alba × P. glandulosa, including axillary buds, young leaves, functional leaves, cambium, xylem, and roots, and the results indicated that PagERF genes are expressed in all tissues of P. alba × P. glandulosa, especially in roots. Quantitative verification results were consistent with transcriptome data. When P. alba × P. glandulosa seedlings were treated with 6% polyethylene glycol 6000 (PEG6000), the results of RT-qRCR showed that nine PagERF genes responded to drought stress in various tissues. This study provides a new perspective on the roles of PagERF family members in regulating plant growth and development, and responses to stress in P. alba × P. glandulosa. Our study provides a theoretical basis for ERF family research in the future.

BIN2 phosphorylates the Thr280 of CO to restrict its function in promoting Arabidopsis flowering

CONSTANS (CO) is a central regulator of floral initiation in response to photoperiod. In this study, we show that the GSK3 kinase BIN2 physically interacts with CO and the gain-of-function mutant bin2-1 displays late flowering phenotype through down-regulation of FT transcription. Genetic analyses show that BIN2 genetically acts upstream of CO in regulating flowering time. Further, we illustrate that BIN2 phosphorylates the Thr280 residue of CO. Importantly, the BIN2 phosphorylation of Thr280 residue restricts the function of CO in promoting flowering through affecting its DNA-binding activity. Moreover, we reveal that the N-terminal part of CO harboring the B-Box domain mediates the interaction of both CO-CO and BIN2-CO. We find that BIN2 inhibits the formation of CO dimer/oligomer. Taken together, this study reveals that BIN2 regulates flowering time through phosphorylating the Thr280 of CO and inhibiting the CO-CO interaction in Arabidopsis.

Comparative and expression analyses of AP2/ERF genes reveal copy number expansion and potential functions of ERF genes in Solanaceae

BACKGROUND

The AP2/ERF gene family is a superfamily of transcription factors that are important in the response of plants to abiotic stress and development. However, comprehensive research of the AP2/ERF genes in the Solanaceae family is lacking.

RESULTS

Here, we updated the annotation of AP2/ERF genes in the genomes of eight Solanaceae species, as well as Arabidopsis thaliana and Oryza sativa. We identified 2,195 AP2/ERF genes, of which 368 (17%) were newly identified. Based on phylogenetic analyses, we observed expansion of the copy number of these genes, especially those belonging to specific Ethylene-Responsive Factor (ERF) subgroups of the Solanaceae. From the results of chromosomal location and synteny analyses, we identified that the AP2/ERF genes of the pepper (Capsicum annuum), the tomato (Solanum lycopersicum), and the potato (Solanum tuberosum) belonging to ERF subgroups form a tandem array and most of them are species-specific without orthologs in other species, which has led to differentiation of AP2/ERF gene repertory among Solanaceae. We suggest that these genes mainly emerged through recent gene duplication after the divergence of these species. Transcriptome analyses showed that the genes have a putative function in the response of the pepper and tomato to abiotic stress, especially those in ERF subgroups.

CONCLUSIONS

Our findings will provide comprehensive information on AP2/ERF genes and insights into the structural, evolutionary, and functional understanding of the role of these genes in the Solanaceae.

Brassinosteroid signaling positively regulates abscisic acid biosynthesis in response to chilling stress in tomato

Brassinosteroids (BRs) and abscisic acid (ABA) are essential regulators of plant growth and stress tolerance. Although the antagonistic interaction of BRs and ABA is proposed to ensure the balance between growth and defense in model plants, the crosstalk between BRs and ABA in response to chilling in tomato (Solanum lycopersicum), a warm-climate horticultural crop, is unclear. Here, we determined that overexpression of the BR biosynthesis gene DWARF (DWF) or the key BR signaling gene BRASSINAZOLE-RESISTANT1 (BZR1) increases ABA levels in response to chilling stress via positively regulating the expression of the ABA biosynthesis gene 9-CIS-EPOXYCAROTENOID DIOXYGENASE1 (NCED1). BR-induced chilling tolerance was mostly dependent on ABA biosynthesis. Chilling stress or high BR levels decreased the abundance of BRASSINOSTEROID-INSENSITIVE2 (BIN2), a negative regulator of BR signaling. Moreover, we observed that chilling stress increases BR levels and results in the accumulation of BZR1. BIN2 negatively regulated both the accumulation of BZR1 protein and chilling tolerance by suppressing ABA biosynthesis. Our results demonstrate that BR signaling positively regulates chilling tolerance via ABA biosynthesis in tomato. The study has implications in production of warm-climate crops in horticulture.

Genome-wide analysis of AP2/ERF superfamily in Isatis indigotica

OBJECTIVE

AP2/ERF (APETALA2/ethylene-responsive factor) superfamily is one of the largest gene families in plants and has been reported to participate in various biological processes, such as the regulation of biosynthesis of active lignan. However, few studies have investigated the genome-wide role of the AP2/ERF superfamily in Isatis indigotica. This study establishes a complete picture of the AP2/ERF superfamily in I. indigotica and contributes valuable information for further functional characterization of IiAP2/ERF genes and supports further metabolic engineering.

METHODS

To identify the IiAP2/ERF superfamily genes, the AP2/ERF sequences from Arabidopsis thaliana and Brassica rapa were used as query sequences in the basic local alignment search tool. Bioinformatic analyses were conducted to investigate the protein structure, motif composition, chromosome location, phylogenetic relationship, and interaction network of the IiAP2/ERF superfamily genes. The accuracy of omics data was verified by quantitative polymerase chain reaction and heatmap analyses.

RESULTS

One hundred and twenty-six putative IiAP2/ERF genes in total were identified from the I. indigotica genome database in this study. By sequence alignment and phylogenetic analysis, the IiAP2/ERF genes were classified into 5 groups including AP2, ERF, DREB (dehydration-responsive element-binding factor), Soloist and RAV (related to abscisic acid insensitive 3/viviparous 1) subfamilies. Among which, 122 members were unevenly distributed across seven chromosomes. Sequence alignment showed that I. indigotica and A. thaliana had 30 pairs of orthologous genes, and we constructed their interaction network. The comprehensive analysis of gene expression pattern in different tissues suggested that these genes may play a significant role in organ growth and development of I. indigotica. Members that may regulate lignan biosynthesis in roots were also preliminarily identified. Ribonucleic acid sequencing analysis revealed that the expression of 76 IiAP2/ERF genes were up- or down-regulated under salt or drought treatment, among which, 33 IiAP2/ERF genes were regulated by both stresses.

CONCLUSION

This study undertook a genome-wide characterization of the AP2/ERF superfamily in I. indigotica, providing valuable information for further functional characterization of IiAP2/ERF genes and discovery of genetic targets for metabolic engineering.

VyUSPA3, a universal stress protein from the Chinese wild grape Vitis yeshanensis, confers drought tolerance to transgenic V. vinifera

VyUSPA3 from the Chinese wild grape Vitis yeshanensis interacts with ERF105, PUB24 and NF-YB3, and overexpression of the VyUSPA3 gene in V. vinifera cv. 'Thompson Seedless' confers drought tolerance. Drought is a major abiotic stress factor that seriously affects the growth and yield of grapevine. Although many drought-related genes have been identified in Arabidopsis and other plants, the functions of only a few of their counterparts have been revealed in grape. Here, a universal stress protein (USP) A from the Chinese wild grape Vitis yeshanensis, VyUSPA3, was identified and its function was subsequently characterized by overexpressing or silencing the VyUSPA3 gene in V. vinifera cv. 'Thompson Seedless' via Agrobacterium-mediated genetic transformation. After 21 d of the drought treatment, most leaves of the untransformed (UT) 'Thompson Seedless' lines wilted, yet UT lines were less damaged compared to the RNAi-VyUSPA3 lines, nonetheless, the OE-VyUSPA3 lines were mostly unaffected. Meanwhile, OE-VyUSPA3 lines showed smaller stomatal aperture, more developed roots, higher leaf relative water content, proline content, and antioxidant enzyme activities, as well as lower malondialdehyde, H₂O₂ and O₂^•- accumulation than UT lines, but this response pattern was reversed in the RNAi-VyUSPA3 lines. Besides, the transcript levels of four drought-related genes (RD22, RD29B, DREB2A, and NCED1) in OE-VyUSPA3 lines were greater than those in the RNAi-VyUSPA3 and UT lines. In addition, a yeast two-hybrid assay and a bimolecular fluorescence complementation assay confirmed that VyUSPA3 interacted with ERF105, PUB24, and NF-YB3, respectively. This study revealed that VyUSPA3 improved drought tolerance in transgenic grapevines possibly through interaction with the hormone signaling, ubiquitination system, ethylene-responsive element binding factor and nuclear factors.

TaERF87 and TaAKS1 synergistically regulate TaP5CS1/TaP5CR1-mediated proline biosynthesis to enhance drought tolerance in wheat

Drought stress limits wheat production and threatens food security world-wide. While ethylene-responsive factors (ERFs) are known to regulate plant response to drought stress, the regulatory mechanisms responsible for a tolerant phenotype remain unclear. Here, we describe the positive regulatory role of TaERF87 in mediating wheat tolerance to drought stress. TaERF87 overexpression (OE) enhances drought tolerance, while silencing leads to drought sensitivity in wheat. RNA sequencing with biochemical assays revealed that TaERF87 activates the expression of the proline biosynthesis genes TaP5CS1 and TaP5CR1 via direct binding to GCC-box elements. Furthermore, proline accumulates to higher levels in TaERF87- and TaP5CS1-OE lines than that in wild-type plants under well-watered and drought stress conditions concomitantly with enhanced drought tolerance in these transgenic lines. Moreover, the interaction between TaERF87 and the bHLH transcription factor TaAKS1 synergistically enhances TaP5CS1 and TaP5CR1 transcriptional activation. TaAKS1 OE also increases wheat drought tolerance by promoting proline accumulation. Additionally, our findings verified that TaERF87 and TaAKS1 are targets of abscisic acid-responsive element binding factor 2 (TaABF2). Together, our study elucidates the mechanisms underlying a positive response to drought stress mediated by the TaABF2-TaERF87/TaAKS1-TaP5CS1/TaP5CR1 module, and identifies candidate genes for the development of elite drought-tolerant wheat varieties.

Genome-Wide Identification of AP2/ERF Superfamily Genes in Juglans mandshurica and Expression Analysis under Cold Stress

Juglans mandshurica has strong freezing resistance, surviving temperatures as low as -40 °C, making it an important freeze tolerant germplasm resource of the genus Juglans. APETALA2/ethylene responsive factor (AP2/ERF) is a plant-specific superfamily of transcription factors that regulates plant development, growth, and the response to biotic and abiotic stress. In this study, phylogenetic analysis was used to identify 184 AP2/ERF genes in the J. mandshurica genome, which were classified into five subfamilies (JmAP2, JmRAV, JmSoloist, JmDREB, and JmERF). A significant amount of discordance was observed in the 184 AP2/ERF genes distribution of J. mandshurica throughout its 16 chromosomes. Duplication was found in 14 tandem and 122 segmental gene pairs, which indicated that duplications may be the main reason for JmAP2/ERF family expansion. Gene structural analysis revealed that 64 JmAP2/ERF genes contained introns. Gene evolution analysis among Juglandaceae revealed that J. mandshurica is separated by 14.23 and 15 Mya from Juglans regia and Carya cathayensis, respectively. Based on promoter analysis in J. mandshurica, many cis-acting elements were discovered that are related to light, hormones, tissues, and stress response processes. Proteins that may contribute to cold resistance were selected for further analysis and were used to construct a cold regulatory network based on GO annotation and JmAP2/ERF protein interaction network analysis. Expression profiling using qRT-PCR showed that 14 JmAP2/ERF genes were involved in cold resistance, and that seven and five genes were significantly upregulated under cold stress in female flower buds and phloem tissues, respectively. This study provides new light on the role of the JmAP2/ERF gene in cold stress response, paving the way for further functional validation of JmAP2/ERF TFs and their application in the genetic improvement of Juglans and other tree species.

HOP1 and HOP2 are involved in salt tolerance by facilitating the brassinosteroid-related nucleo-cytoplasmic partitioning of the HSP90-BIN2 complex

The co-chaperone heat shock protein (HSP)70-HSP90 organizing protein (HOP) is involved in plant thermotolerance. However, its function in plant salinity tolerance was not yet studied. We found that Arabidopsis HOP1 and HOP2 play critical roles in salt tolerance by affecting the nucleo-cytoplasmic partitioning of HSP90 and brassinosteroid-insensitive 2 (BIN2). A hop1/2 double mutant was hypersensitive to salt-stress. Interestingly, this sensitivity was remedied by exogenous brassinolide application, while the application of brassinazole impeded growth of both wild-type (WT) and hop1/2 plants under normal and salt stress conditions. This suggested that the insufficient brassinosteroid (BR) content was responsible for the salt-sensitivity of hop1/2. After WT was transferred to salt stress conditions, HOP1/2, BIN2 and HSP90 accumulated in the nucleus, brassinazole-resistant 1 (BZR1) was phosphorylated and accumulated in the cytoplasm, and BR content significantly increased. This initial response resulted in dephosphorylation of BZR1 and BR response. This dynamic regulation of BR content was impeded in salt-stressed hop1/2. Thus, we propose that HOP1 and HOP2 are involved in salt tolerance by affecting BR signalling.

A role for brassinosteroid signalling in decision-making processes in the Arabidopsis seedling

Plants often adapt to adverse conditions via differential growth, whereby limited resources are discriminately allocated to optimize the growth of one organ at the expense of another. Little is known about the decision-making processes that underly differential growth. In this study, we developed a screen to identify decision making mutants by deploying two tools that have been used in decision theory: a well-defined yet limited budget, as well as conflict-of-interest scenarios. A forward genetic screen that combined light and water withdrawal was carried out. This identified BRASSINOSTEROID INSENSITIVE 2 (BIN2) alleles as decision mutants with "confused" phenotypes. An assessment of organ and cell length suggested that hypocotyl elongation occurred predominantly via cellular elongation. In contrast, root growth appeared to be regulated by a combination of cell division and cell elongation or exit from the meristem. Gain- or loss- of function bin2 mutants were most severely impaired in their ability to adjust cell geometry in the hypocotyl or cell elongation as a function of distance from the quiescent centre in the root tips. This study describes a novel paradigm for root growth under limiting conditions, which depends not only on hypocotyl-versus-root trade-offs in the allocation of limited resources, but also on an ability to deploy different strategies for root growth in response to multiple stress conditions.

Genome-Wide Analysis of AP2/ERF Gene Superfamily in Ramie (Boehmeria nivea L.) Revealed Their Synergistic Roles in Regulating Abiotic Stress Resistance and Ramet Development

AP2/ERF transcription factors (TFs) are one of the largest superfamilies in plants, and play vital roles in growth and response to biotic/abiotic stresses. Although the AP2/ERF family has been extensively characterized in many species, very little is known about this family in ramie (Boehmeria nivea L.). In this study, 138 AP2/ERF TFs were identified from the ramie genome and were grouped into five subfamilies, including the AP2 (19), RAV (5), Soloist (1), ERF (77), and DREB (36). Unique motifs were found in the DREB/ERF subfamily members, implying significance to the AP2/ERF TF functions in these evolutionary branches. Segmental duplication events were found to play predominant roles in the BnAP2/ERF TF family expansion. Light-, stress-, and phytohormone-responsive elements were identified in the promoter region of BnAP2/ERF genes, with abscisic acid response elements (ABRE), methyl jasmonate response elements, and the dehydration response element (DRE) being dominant. The integrated transcriptome and quantitative real-time PCR (qPCR) revealed 12 key BnAP2/ERF genes positively responding to waterlogging. Five of the genes are also involved in ramet development, with two (BnERF-30 and BnERF-32) further showing multifunctional roles. The protein interaction prediction analysis further verified their crosstalk mechanism in coordinating waterlogging resistance and ramet development. Our study provides new insights into the presence of AP2/ERF TFs in ramie, and provides candidate AP2/ERF TFs for further studies on breeding varieties with coupling between water stress tolerance and high yield.

Identification and Characterization of AP2/ERF Transcription Factors in Yellow Horn

The AP2/ERF gene family involves numerous plant processes, including growth, development, metabolism, and various plant stress responses. However, several studies have been conducted on the AP2/ERF gene family in yellow horn, a new type of oil woody crop and an essential oil crop in China. According to sequence alignment and phylogenetic analyses, one hundred and forty-five AP2/ERF genes were detected from the yellow horn genome. They were divided into four relatively conserved subfamilies, including 21 AP2 genes, 119 ERBP genes, 4 RAV genes, and 1 Soloist gene. Gene analysis of XsAP2/ERF TFs showed 87 XsAP2/ERF TFs lacked introns. There were 75 pairs of collinearity relationships between X. sorbifolium and Arabidopsis, indicating a close similarity. In addition, the expression patterns of XsAP2/ERF TFs under cold treatments confirmed that the XsAP2/ERF TFs play essential roles in abiotic stress response. The expression of eight XsAP2/ERF transcription factors was verified in different tissues and under various stress treatments using RT-qPCR. This study establishes a starting point for further research to explore the potential mechanisms of identifying candidate AP2/ERF TFs that could respond to the abiotic stress of yellow horn.

ERF subfamily transcription factors and their function in plant responses to abiotic stresses

Ethylene Responsive Factor (ERF) subfamily comprise the largest number of proteins in the plant AP2/ERF superfamily, and have been most extensively studied on the biological functions. Members of this subfamily have been proven to regulate plant resistances to various abiotic stresses, such as drought, salinity, chilling and some other adversities. Under these stresses, ERFs are usually activated by mitogen-activated protein kinase induced phosphorylation or escape from ubiquitin-ligase enzymes, and then form complex with nucleic proteins before binding to cis-element in promoter regions of stress responsive genes. In this review, we will discuss the phylogenetic relationships among the ERF subfamily proteins, summarize molecular mechanism how the transcriptional activity of ERFs been regulated and how ERFs of different subgroup regulate the transcription of stress responsive genes, such as high-affinity K⁺ transporter gene PalHKT1;2, reactive oxygen species related genes LcLTP, LcPrx, and LcRP, flavonoids synthesis related genes FtF3H and LhMYBSPLATTER, etc. Though increasing researches demonstrate that ERFs are involved in various abiotic stresses, very few interact proteins and target genes of them have been comprehensively annotated. Hence, future research prospects are described on the mechanisms of how stress signals been transited to ERFs and how ERFs regulate the transcriptional expression of stress responsive genes.

Transcriptome analysis reveals key drought-stress-responsive genes in soybean

Drought is the most common environmental stress and has had dramatic impacts on soybean (Glycine max L.) growth and yield worldwide. Therefore, to investigate the response mechanism underlying soybean resistance to drought stress, the drought-sensitive cultivar "Liaodou 15" was exposed to 7 (mild drought stress, LD), 17 (moderate drought stress, MD) and 27 (severe drought stress, SD) days of drought stress at the flowering stage followed by rehydration until harvest. A total of 2214, 3684 and 2985 differentially expressed genes (DEGs) in LD/CK1, MD/CK2, and SD/CK3, respectively, were identified by RNA-seq. Weighted gene co-expression network analysis (WGCNA) revealed the drought-response TFs such as WRKY (Glyma.15G021900, Glyma.15G006800), MYB (Glyma.15G190100, Glyma.15G237900), and bZIP (Glyma.15G114800), which may be regulated soybean drought resistance. Second, Glyma.08G176300 (NCED1), Glyma.03G222600 (SDR), Glyma.02G048400 (F3H), Glyma.14G221200 (CAD), Glyma.14G205200 (C4H), Glyma.19G105100 (CHS), Glyma.07G266200 (VTC) and Glyma.15G251500 (GST), which are involved in ABA and flavonoid biosynthesis and ascorbic acid and glutathione metabolism, were identified, suggesting that these metabolic pathways play key roles in the soybean response to drought. Finally, the soybean yield after rehydration was reduced by 50% under severe drought stress. Collectively, our study deepens the understanding of soybean drought resistance mechanisms and provides a theoretical basis for the soybean drought resistance molecular breeding and effectively adjusts water-saving irrigation for soybean under field production.

Field evaluation of TaDREB2B-ectopic expression sugarcane (Saccharum spp. hybrid) for drought tolerance

Sugarcane is one of the most crucial sugar crops globally that supplies the main raw material for sugar and ethanol production, but drought stress causes a severe decline in sugarcane yield worldwide. Enhancing sugarcane drought resistance and reducing yield and quality losses is an ongoing challenge in sugarcane genetic improvement. Here, we introduced a Tripidium arundinaceum dehydration-responsive element-binding transcription factor (TaDREB2B) behind the drought-responsible RD29A promoter into a commercial sugarcane cultivar FN95-1702 and subsequently conducted a series of drought tolerance experiments and investigation of agronomic and quality traits. Physiological analysis indicated that Prd29A: TaDREB2B transgenic sugarcane significantly confers drought tolerance in both the greenhouses and the field by enhancing water retention capacity and reducing membrane damage without compromising growth. These transgenic plants exhibit obvious improvements in yield performance and various physiological traits under the limited-irrigation condition in the field, such as increasing 41.9% yield and 44.4% the number of ratooning sugarcane seedlings. Moreover, Prd29A: TaDREB2B transgenic plants do not penalize major quality traits, including sucrose content, gravity purity, Brix, etc. Collectively, our results demonstrated that the Prd29A-TaDREB2B promoter-transgene combination will be a useful biotechnological tool for the increase of drought tolerance and the minimum of yield losses in sugarcane.

Integration of multi-omics data reveals interplay between brassinosteroid and Target of Rapamycin Complex signaling in Arabidopsis

Brassinosteroids (BRs) and Target of Rapamycin Complex (TORC) are two major actors coordinating plant growth and stress responses. Brassinosteroids function through a signaling pathway to extensively regulate gene expression and TORC is known to regulate translation and autophagy. Recent studies have revealed connections between these two pathways, but a system-wide view of their interplay is still missing. We quantified the level of 23 975 transcripts, 11 183 proteins, and 27 887 phosphorylation sites in wild-type Arabidopsis thaliana and in mutants with altered levels of either BRASSINOSTEROID INSENSITIVE 2 (BIN2) or REGULATORY ASSOCIATED PROTEIN OF TOR 1B (RAPTOR1B), two key players in BR and TORC signaling, respectively. We found that perturbation of BIN2 or RAPTOR1B levels affects a common set of gene-products involved in growth and stress responses. Furthermore, we used the multi-omic data to reconstruct an integrated signaling network. We screened 41 candidate genes identified from the reconstructed network and found that loss of function mutants of many of these proteins led to an altered BR response and/or modulated autophagy activity. Altogether, these results establish a predictive network that defines different layers of molecular interactions between BR- or TORC-regulated growth and autophagy.

OsDREB2B, an AP2/ERF transcription factor, negatively regulates plant height by conferring GA metabolism in rice

The AP2/ERF family is a large group of plant-specific transcription factors that play an important role in many biological processes, such as growth, development, and abiotic stress responses. OsDREB2B, a dehydration responsive factor (DRE/CRT) in the DREB subgroup of the AP2/ERF family, is associated with abiotic stress responses, such as cold, drought, salt, and heat stress, in Arabidopsis or rice. However, its role in regulating plant growth and development in rice is unclear. In this study, we reported a new function of OsDREB2B, which negatively regulates plant height in rice. Compared with wild type (WT), OsDREB2B-overexpressing (OE) rice exhibited dwarf phenotypes, such as reduction in plant height, internode length, and seed length, as well as grain yield, while the knockout mutants developed by CRISPR/Cas9 technology exhibited similar phenotypes. Spatial expression analysis revealed that OsDREB2B was highly expressed in the leaf sheaths. Under exogenous GA₃ application, OsDREB2B expression was induced, and the length of the second leaf sheath of the OsDREB2B-OE lines recovered to that of the WT. OsDREB2B localized to the nucleus of the rice protoplast acted as a transcription activator and upregulated OsAP2-39 by directly binding to its promoter. OsDREB2B-OE lines reduced endogenous bioactive GA levels by downregulating seven GA biosynthesis genes and upregulating eight GA deactivation genes but not GA signaling genes. The yeast two-hybrid assay and bimolecular fluorescence complementation assay showed that OsDREB2B interacted with OsWRKY21. In summary, our study suggests that OsDREB2B plays a negative role in rice growth and development by regulating GA metabolic gene expression, which is mediated by OsAP2-39 and OsWRKY21, thereby reducing GA content and rice plant height.

Role of pepper MYB transcription factor CaDIM1 in regulation of the drought response

Abscisic acid (ABA) is a major phytohormone that plays important roles in stress responses, including regulation of gene expression and stomatal closure. Regulation of gene expression by transcription factors is a key cellular process for initiating defense responses to biotic and abiotic stresses. Here, using pepper (Capsicum annuum) leaves, we identified the MYB transcription factor CaDIM1 (Capsicum annuum Drought Induced MYB 1), which was highly induced by ABA and drought stress. CaDIM1 has an MYB domain in the N-terminal region and an acidic domain in the C-terminal region, which are responsible for recognition and transactivation of the target gene, respectively. Compared to control plants, CaDIM1-silenced pepper plants displayed ABA-insensitive and drought-sensitive phenotypes with reduced expression of stress-responsive genes. On the other hand, overexpression of CaDIM1 in Arabidopsis exhibited the opposite phenotypes of CaDIM1-silenced pepper plants, accompanied by enhanced ABA sensitivity and drought tolerance. Taken together, we demonstrate that CaDIM1 functions as a positive regulator of the drought-stress response via modulating ABA-mediated gene expression.

Salicylic acid-activated BIN2 phosphorylation of TGA3 promotes Arabidopsis PR gene expression and disease resistance

The plant defense hormone, salicylic acid (SA), plays essential roles in immunity and systemic acquired resistance. Salicylic acid induced by the pathogen is perceived by the receptor nonexpressor of pathogenesis-related genes 1 (NPR1), which is recruited by TGA transcription factors to induce the expression of pathogenesis-related (PR) genes. However, the mechanism by which post-translational modifications affect TGA's transcriptional activity by salicylic acid signaling/pathogen infection is not well-established. Here, we report that the loss-of-function mutant of brassinosteroid insensitive2 (BIN2) and its homologs, bin2-3 bil1 bil2, causes impaired pathogen resistance and insensitivity to SA-induced PR gene expression, whereas the gain-of-function mutant, bin2-1, exhibited enhanced SA signaling and immunity against the pathogen. Our results demonstrate that salicylic acid activates BIN2 kinase, which in turn phosphorylates TGA3 at Ser33 to enhance TGA3 DNA binding ability and NPR1-TGA3 complex formation, leading to the activation of PR gene expression. These findings implicate BIN2 as a new component of salicylic acid signaling, functioning as a key node in balancing brassinosteroid-mediated plant growth and SA-induced immunity.