Benefits of brassinosteroid crosstalk

The role of strigolactones in resistance to environmental stress in plants

Abiotic stress impairs plant growth and development, thereby causing low yield and inferior quality of crops. Increasing studies reported that strigolactones (SL) are plant hormones that enhance plant stress resistance by regulating plant physiological processes and gene expressions. In this review, we introduce the response and regulatory role of SL in salt, drought, light, heat, cold and cadmium stresses in plants. This review also discusses how SL alleviate the damage of abiotic stress in plants, furthermore, introducing the mechanisms of SL enhancing plant stress resistance at the genetic level. Under abiotic stress, the exogenous SL analog GR24 can induce the biosynthesis of SL in plants, and endogenous SL can alleviate the damage caused by abiotic stress. SL enhanced the stress resistance of plants by protecting photosynthesis, enhancing the antioxidant capacity of plants and promoting the symbiosis between plants and arbuscular mycorrhiza (AM). SL interact with abscisic acid (ABA), salicylic acid (SA), auxin, cytokinin (CK), jasmonic acid (JA), hydrogen peroxide (H2O2) and other signal molecules to jointly regulate plant stress resistance. Lastly, both the importance of SL and their challenges for future work are outlined in order to further elucidate the specific mechanisms underlying the roles of SL in plant responses to abiotic stress.

Exogenous melatonin prolongs raspberry postharvest life quality by increasing some antioxidant and enzyme activity and phytochemical contents

There is a growing trend towards enhancing the post-harvest shelf life and maintaining the nutritional quality of horticultural products using eco-friendly methods. Raspberries are valued for their diverse array of phenolic compounds, which are key contributors to their health-promoting properties. However, raspberries are prone to a relatively short post-harvest lifespan. The present study aimed to investigate the effect of exogenous melatonin (MEL; 0, 0.001, 0.01, and 0.1 mM) on decay control and shelf-life extension. The results demonstrated that MEL treatment significantly reduced the fruit decay rate (P ≤ 0.01). Based on the findings, MEL treatment significantly increased titratable acidity (TA), total phenolics content (TPC), total flavonoid content (TFC), and total anthocyanin content (TAC). Furthermore, the MEL-treated samples showed increased levels of rutin and quercetin content, as well as antioxidant activity as measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reduction activity potential (FRAP). Additionally, the samples exhibited higher levels of phenylalanine ammonia-lyase (PAL) and catalase (CAT) enzymes compared to the control samples. Moreover, the levels of pH, total soluble solids (TSS), and IC50 were decreased in the MEL-treated samples (P ≤ 0.01). The highest amount of TA (0.619 g/100 ml juice), rutin (16.722 µg/ml juice) and quercetin (1.467 µg/ml juice), and PAL activity (225.696 nm/g FW/min) was observed at 0.001 mM treatment, while, the highest amount of TAC (227.235 mg Cy-g/100 ml juice) at a concentration of 0.01 mM and CAT (0.696 u/g FW) and TAL activities (9.553 nm/100 g FW) at a concentration of 0.1 mM were obtained. Considering the lack of significant differences in the effects of melatonin concentrations and the low dose of 0.001 mM, this concentration is recommended for further research. The hierarchical cluster analysis (HCA) and principal component analysis (PCA) divided the treatments into three groups based on their characteristics. Based on the Pearson correlation between TPC, TFC, TAC, and TAA, a positive correlation was observed with antioxidant (DPPH and FRAP) and enzyme (PAL and CAT) activities. The results of this study have identified melatonin as an eco-friendly compound that enhances the shelf life of raspberry fruits by improving phenolic compounds, as well as antioxidant and enzyme activities.

Homobrassinolide Delays Huanglongbing Progression in Newly Planted Citrus (Citrus sinensis) Trees

Huanglongbing (HLB), or citrus greening, is a devastating disease impacting citrus trees worldwide, with severe effects particularly noted in Florida. Current strategies to combat HLB focus on aggressive replanting, despite the high susceptibility of young trees to infection. In this context, it is critical to explore agronomic practices that can enhance the health and resistance of young citrus trees to HLB. Here, we demonstrate that treatment with homobrassinolide (HBr), a type of brassinosteroid, in newly planted citrus (Citrus sinensis) trees can delay HLB infection and improve tree health amidst the high psyllid pressure conditions endemic to Florida. Our study reveals a significant reduction in HLB infection rates in HBr-treated trees compared to control trees, with only 25% of treated trees testing positive for HLB by six months, in contrast to 100% infection in untreated trees. This delay in infection may be attributed to HBr inducing an immune response and negatively impacting psyllid performance, as subsequently demonstrated in a greenhouse experiment. Our findings suggest that HBr applications could serve as a viable strategy to enhance the resilience of citrus production against HLB, underscoring the need for further investigation into their mechanisms of action and potential role in a comprehensive pest and disease management strategy.

Genome-Wide Identification, Characterization, and Expression Analysis of the BES1 Family Genes under Abiotic Stresses in Phoebe bournei

The BRI1 EMS suppressor 1(BES1) transcription factor is a crucial regulator in the signaling pathway of Brassinosteroid (BR) and plays an important role in plant growth and response to abiotic stress. Although the identification and functional validation of BES1 genes have been extensively explored in various plant species, the understanding of their role in woody plants-particularly the endangered species Phoebe bournei (Hemsl.) Yang-remains limited. In this study, we identified nine members of the BES1 gene family in the genome of P. bournei; these nine members were unevenly distributed across four chromosomes. In our further evolutionary analysis of PbBES1, we discovered that PbBES1 can be divided into three subfamilies (Class I, Class II, and Class IV) based on the evolutionary tree constructed with Arabidopsis thaliana, Oryza sativa, and Solanum lycopersicum. Each subfamily contains 2-5 PbBES1 genes. There were nine pairs of homologous BES1 genes in the synteny analysis of PbBES1 and AtBES1. Three segmental replication events and one pair of tandem duplication events were present among the PbBES1 family members. Additionally, we conducted promoter cis-acting element analysis and discovered that PbBES1 contains binding sites for plant growth and development, cell cycle regulation, and response to abiotic stress. PbBES1.2 is highly expressed in root bark, stem bark, root xylem, and stem xylem. PbBES1.3 was expressed in five tissues. Moreover, we examined the expression profiles of five representative PbBES1 genes under heat and drought stress. These experiments preliminarily verified their responsiveness and functional roles in mediating responses to abiotic stress. This study provides important clues to elucidate the functional characteristics of the BES1 gene family, and at the same time provides new insights and valuable information for the regulation of resistance in P. bournei.

Enhanced Susceptibility to Tomato Chlorosis Virus (ToCV) in Hsp90- and Sgt1-Silenced Plants: Insights from Gene Expression Dynamics

The emerging whitefly-transmitted crinivirus tomato chlorosis virus (ToCV) causes substantial economic losses by inducing yellow leaf disorder in tomato crops. This study explores potential resistance mechanisms by examining early-stage molecular responses to ToCV. A time-course transcriptome analysis compared naïve, mock, and ToCV-infected plants at 2, 7, and 14 days post-infection (dpi). Gene expression changes were most notable at 2 and 14 dpi, likely corresponding to whitefly feeding and viral infection. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed key genes and pathways associated with ToCV infection, including those related to plant immunity, flavonoid and steroid biosynthesis, photosynthesis, and hormone signaling. Additionally, virus-derived small interfering RNAs (vsRNAs) originating from ToCV predominantly came from RNA2 and were 22 nucleotides in length. Furthermore, two genes involved in plant immunity, Hsp90 (heat shock protein 90) and its co-chaperone Sgt1 (suppressor of the G2 allele of Skp1) were targeted through viral-induced gene silencing (VIGS), showing a potential contribution to basal resistance against viral infections since their reduction correlated with increased ToCV accumulation. This study provides insights into tomato plant responses to ToCV, with potential implications for developing effective disease control strategies.

Assessing the effects of 24-epibrassinolide and yeast extract at various levels on cowpea's morphophysiological and biochemical responses under water deficit stress

BACKGROUND

Due to the factor of water deficit, which has placed human food security at risk by causing a 20% annual reduction in agricultural products, addressing this growing peril necessitates the adoption of inventive strategies aimed at enhancing plant tolerance. One such promising approach is employing elicitors such as 24-epibrassinolide (EBR) and yeast extract, which are potent agents capable of triggering robust defense responses in plants. By employing these elicitors, crops can develop enhanced adaptive mechanisms to combat water deficit and improve their ability to withstand drought condition. This study investigates the impact of different levels of EBR (0, 5, 10 µm) and yeast extract (0 and 12 g/l) on enhancing the tolerance of cowpea to water deficit stress over two growing seasons.

RESULTS

The findings of this study demonstrate that, the combined application of EBR (especially 10 µm) and yeast extract (12 g/l) can increase seed yield (18%), 20-pod weight (16%), the number of pods per plant (18%), total chlorophyll content (90%), and decrease malondialdehyde content (45%) in cowpea, compared to plants grown under water deficit stress without these treatments. Upon implementing these treatments, impressive results were obtained, with the highest recorded values observed for the seed yield (1867.55 kg/ha), 20-pod weight (16.29 g), pods number per plant (9), and total chlorophyll content (19.88 mg g-1 FW). The correlation analysis indicated a significant relationship between the seed yield, and total chlorophyll (0.74**), carotenoids (0.82**), weight of 20 seeds (0.67**), and number of pods (0.90**). These traits should be prioritized in cowpea breeding programs focusing on water deficit stress.

CONCLUSIONS

The comprehensive exploration of the effects of EBR and yeast extract across various levels on cowpea plants facing water deficit stress presents a pivotal contribution to the agricultural domain. This research illuminates a promising trajectory for future agricultural practices and users seeking sustainable solutions to enhance crops tolerance. Overall, the implications drawn from this study contribute significantly towards advancing our understanding of plant responses to water deficit stress while providing actionable recommendations for optimizing crop production under challenging environmental conditions.

Influence of Exogenous 24-Epicasterone on the Hormonal Status of Soybean Plants

Brassinosteroids (BRs) are key phytohormones involved in the regulation of major processes of cell metabolism that guide plant growth. In the past decades, new evidence has made it clear that BRs also play a key role in the orchestration of plant responses to many abiotic and biotic stresses. In the present work, we analyzed the impact of foliar treatment with 24-epicastasterone (ECS) on the endogenous content of major phytohormones (auxins, salicylic acid, jasmonic acid, and abscisic acid) and their intermediates in soybean leaves 7 days following the treatment. Changes in the endogenous content of phytohormones have been identified and quantified by LC/MS. The obtained results point to a clear role of ECS in the upregulation of auxin content (indole-3-acetic acid, IAA) and downregulation of salicylic, jasmonic, and abscisic acid levels. These data confirm that under optimal conditions, ECS in tested concentrations of 0.25 µM and 1 µM might promote growth in soybeans by inducing auxin contents. Benzoic acid (a precursor of salicylic acid (SA)), but not SA itself, has also been highly accumulated under ECS treatment, which indicates an activation of the adaptation strategies of cell metabolism to possible environmental challenges.

Novel Insights into Exogenous Phytohormones: Central Regulators in the Modulation of Physiological, Biochemical, and Molecular Responses in Rice under Metal(loid) Stress

Rice (Oryza sativa) is a research model for monocotyledonous plants. Rice is also one of the major staple foods and the primary crop for more than half of the world's population. Increasing industrial activities and the use of different fertilizers and pesticides containing heavy metals (HMs) contribute to the contamination of agriculture fields. HM contamination is among the leading causes that affect the health of rice plants by limiting their growth and causing plant death. Phytohormones have a crucial role in stress-coping mechanisms and in determining a range of plant development and growth aspects during heavy metal stress. This review summarizes the role of different exogenous applications of phytohormones including auxin, cytokinin, gibberellins, ethylene, abscisic acid, strigolactones, jasmonates, brassinosteroids, and salicylic acids in rice plants for mitigating heavy metal stress via manipulation of their stress-related physiological and biochemical processes, and alterations of signaling and biosynthesis of genes. Exogenous administration of phytohormones and regulation of endogenous levels by targeting their biosynthesis/signaling machineries is a potential strategy for protecting rice from HM stress. The current review primarily emphasizes the key mechanistic phytohormonal-mediated strategies for reducing the adverse effects of HM toxicity in rice. Herein, we have provided comprehensive evidence for the effective role of exogenous phytohormones in employing defense responses and tolerance in rice to the phytotoxic effects of HM toxicity along with endogenous hormonal crosstalk for modulation of subcellular mechanisms and modification of stress-related signaling pathways, and uptake and translocation of metals. Altogether, this information offers a systematic understanding of how phytohormones modulate a plant's tolerance to heavy metals and may assist in directing the development of new approaches to strengthen rice plant resistance to HM toxicity.

Characterization and gene expression patterns analysis implies BSK family genes respond to salinity stress in cotton

Identification, evolution, and expression patterns of BSK (BR signaling kinase) family genes revealed that BSKs participated in the response of cotton to abiotic stress and maintained the growth of cotton in extreme environment. The steroidal hormone brassinosteroids (BR) play important roles in different plant biological processes. This study focused on BSK which were downstream regulatory element of BR, in order to help to decipher the functions of BSKs genes from cotton on growth development and responses to abiotic stresses and lean the evolutionary relationship of cotton BSKs. BSKs are a class of plant-specific receptor-like cytoplasmic kinases involved in BR signal transduction. In this study, bioinformatics methods were used to identify the cotton BSKs gene family at the cotton genome level, and the gene structure, promoter elements, protein structure and properties, gene expression patterns and candidate interacting proteins were analyzed. In the present study, a total of 152 BSKs were identified by a genome-wide search in four cotton species and other 11 plant species, and phylogenetic analysis revealed three evolutionary clades. It was identified that BSKs contain typical PKc and TPR domains, the N-terminus is composed of extended chains and helical structures. Cotton BSKs genes show different expression patterns in different tissues and organs. The gene promoter contains numerous cis-acting elements induced by hormones and abiotic stress, the hormone ABA and Cold-inducing related elements have the highest count, indicating that cotton BSK genes may be regulated by various hormones at different growth stages and involved in the response regulation of cotton to various stresses. The expression analysis of BSKs in cotton showed that the expression levels of GhBSK06, GhBSK10, GhBSK21 and GhBSK24 were significantly increased with salt-inducing. This study is helpful to analyze the function of cotton BSKs genes in growth and development and in response to stress.

Reciprocal inhibition of expression between RAV1 and BES1 modulates plant growth and development in Arabidopsis

RAV1 (Related to ABI3/VP1) is a plant-specific B3 and AP2 domain-containing transcription factor that acts as a negative regulator of growth in many plant species. The expression of RAV1 is downregulated by brassinosteroids (BRs); large-scale transcriptome analyses have shown that the expression of RAV1 was previously targeted by BRI1-EMS-SUPPRESOR1 (BES1) and BRASSINAZOLE-RESISTANT1 (BZR1), which are critical transcription factors for the BR-signaling process. Using RAV1-overexpressing transgenic plants, we showed that RAV1 overexpression reduced the BR signaling capacity, resulting in the downregulation of BR biosynthetic genes and BES1 expression. Furthermore, we demonstrated that BES1, not BZR1, is directly bound to the RAV1 promoter and repressed RAV1 expression, and vice versa; RAV1 is also bound to the BES1 promoter and repressed BES1 expression. This mutual inhibition was specific to RAV1 and BES1 because RAV1 exhibited binding activity to the BZR1 promoter but did not repress BZR1 expression. We observed that constitutively activated BR signaling phenotypes in bes1-D were attenuated by the repression of endogenous BES1 expression in transgenic bes1-D plants overexpressing RAV1. RNA-sequencing analysis of RAV1-overexpressing transgenic plants and bes1-D mutant plants revealed differentially expressed genes by RAV1 and BES1 and genes that were oppositely co-regulated by RAV1 and BES1. RAV1 and BES1 regulated different transcriptomes but co-regulated a specific set of genes responsible for the balance between growth and defense. These results suggested that the mutual inhibitory transcriptional activities of RAV1 and BES1 provide fine regulatory mechanisms for plant growth and development.

A necessary considering factor for breeding: growth-defense tradeoff in plants

Crop diseases cause enormous yield losses and threaten global food security. Deployment of resistant cultivars can effectively control the disease and to minimize crop losses. However, high level of genetic immunity to disease was often accompanied by an undesired reduction in crop growth and yield. Recently, literatures have been rapidly emerged in understanding the mechanism of disease resistance and development genes in crop plants. To determine how and why the costs and the likely benefit of resistance genes caused in crop varieties, we re-summarized the present knowledge about the crosstalk between plant development and disease resistance caused by those genes that function as plasma membrane residents, MAPK cassette, nuclear envelope (NE) channels components and pleiotropic regulators. Considering the growth-defense tradeoffs on the basis of current advances, finally, we try to understand and suggest that a reasonable balancing strategies based on the interplay between immunity with growth should be considered to enhance immunity capacity without yield penalty in future crop breeding.

Brassinosteroids mediate moderate soil-drying to alleviate spikelet degeneration under high temperature during meiosis of rice

This study tested the hypothesis that brassinosteroids (BRs) mediate moderate soil-drying (MD) to alleviate spikelet degeneration under high temperature (HT) stress during meiosis of rice (Oryza sativa L.). A rice cultivar was pot-grown and subjected to normal temperature (NT) and HT treatments during meiosis, and two irrigation regimes including well-watered (WW) and MD were imposed to the plants simultaneously. The MD effectively alleviated the spikelet degeneration and yield loss under HT stress mainly via improving root activity and canopy and panicle traits including higher photosynthetic capacity, tricarboxylic acid cycle activity, and antioxidant capacity than WW. These parameters were regulated by BRs levels in plants. The decrease in BRs levels at HT was due mainly to the enhanced BRs decomposition, and the MD could rescue the BRs deficiency at HT via enhancing BRs biosynthesis and impeding decomposition. The connection between BRs and HT was verified by using rice BRs-deficient mutants, transgenic rice lines, and chemical regulators. Similar results were obtained in the open-air field experiment. The results suggest that BRs can mediate the MD to alleviate spikelet degeneration under HT stress during meiosis mainly via enhancing root activity, canopy traits, and young panicle traits of rice.

Application of Data Modeling, Instrument Engineering and Nanomaterials in Selected Medid the Scientific Recinal Plant Tissue Culture

At present, most precious compounds are still obtained by plant cultivation such as ginsenosides, glycyrrhizic acid, and paclitaxel, which cannot be easily obtained by artificial synthesis. Plant tissue culture technology is the most commonly used biotechnology tool, which can be used for a variety of studies such as the production of natural compounds, functional gene research, plant micropropagation, plant breeding, and crop improvement. Tissue culture material is a basic and important part of this issue. The formation of different plant tissues and natural products is affected by growth conditions and endogenous substances. The accumulation of secondary metabolites are affected by plant tissue type, culture method, and environmental stress. Multi-domain technologies are developing rapidly, and they have made outstanding contributions to the application of plant tissue culture. The modes of action have their own characteristics, covering the whole process of plant tissue from the induction, culture, and production of natural secondary metabolites. This paper reviews the induction mechanism of different plant tissues and the application of multi-domain technologies such as artificial intelligence, biosensors, bioreactors, multi-omics monitoring, and nanomaterials in plant tissue culture and the production of secondary metabolites. This will help to improve the tissue culture technology of medicinal plants and increase the availability and the yield of natural metabolites.

Molecular evidence for adaptive evolution of drought tolerance in wild cereals

The considerable drought tolerance of wild cereal crop progenitors has diminished during domestication in the pursuit of higher productivity. Regaining this trait in cereal crops is essential for global food security but requires novel genetic insight. Here, we assessed the molecular evidence for natural variation of drought tolerance in wild barley (Hordeum spontaneum), wild emmer wheat (Triticum dicoccoides), and Brachypodium species collected from dry and moist habitats at Evolution Canyon, Israel (ECI). We report that prevailing moist vs dry conditions have differentially shaped the stomatal and photosynthetic traits of these wild cereals in their respective habitats. We present the genomic and transcriptomic evidence accounting for differences, including co-expression gene modules, correlated with physiological traits, and selective sweeps, driven by the xeric site conditions on the African Slope (AS) at ECI. Co-expression gene module 'circadian rhythm' was linked to significant drought-induced delay in flowering time in Brachypodium stacei genotypes. African Slope-specific differentially expressed genes are important in barley drought tolerance, verified by silencing Disease-Related Nonspecific Lipid Transfer 1 (DRN1), Nonphotochemical Quenching 4 (NPQ4), and Brassinosteroid-Responsive Ring-H1 (BRH1). Our results provide new genetic information for the breeding of resilient wheat and barley in a changing global climate with increasingly frequent drought events.

Systematic analysis of Histidine photosphoto transfer gene family in cotton and functional characterization in response to salt and around tolerance

BACKGROUND

Phosphorylation regulated by the two-component system (TCS) is a very important approach signal transduction in most of living organisms. Histidine phosphotransfer (HP) is one of the important members of the TCS system. Members of the HP gene family have implications in plant stresses tolerance and have been deeply studied in several crops. However, upland cotton is still lacking with complete systematic examination of the HP gene family.

RESULTS

A total of 103 HP gene family members were identified. Multiple sequence alignment and phylogeny of HPs distributed them into 7 clades that contain the highly conserved amino acid residue "XHQXKGSSXS", similar to the Arabidopsis HP protein. Gene duplication relationship showed the expansion of HP gene family being subjected with whole-genome duplication (WGD) in cotton. Varying expression profiles of HPs illustrates their multiple roles under altering environments particularly the abiotic stresses. Analysis is of transcriptome data signifies the important roles played by HP genes against abiotic stresses. Moreover, protein regulatory network analysis and VIGS mediated functional approaches of two HP genes (GhHP23 and GhHP27) supports their predictor roles in salt and drought stress tolerance.

CONCLUSIONS

This study provides new bases for systematic examination of HP genes in upland cotton, which formulated the genetic makeup for their future survey and examination of their potential use in cotton production.

Abiotic Stress Tolerance in Plants: Brassinosteroids Navigate Competently

Brassinosteroid hormones (BRs) multitask to smoothly regulate a broad spectrum of vital physiological processes in plants, such as cell division, cell expansion, differentiation, seed germination, xylem differentiation, reproductive development and light responses (photomorphogenesis and skotomorphogenesis). Their importance is inferred when visible abnormalities arise in plant phenotypes due to suboptimal or supraoptimal hormone levels. This group of steroidal hormones are major growth regulators, having pleiotropic effects and conferring abiotic stress resistance to plants. Numerous abiotic stresses are the cause of significant loss in agricultural yield globally. However, plants are well equipped with efficient stress combat machinery. Scavenging reactive oxygen species (ROS) is a unique mechanism to combat the deleterious effects of abiotic stresses. In light of numerous reports in the past two decades, the complex BR signaling under different stress conditions (drought, salinity, extreme temperatures and heavy metals/metalloids) that drastically hinders the normal metabolism of plants is gradually being untangled and revealed. Thus, crop improvement has substantial potential by tailoring either the brassinosteroid signaling, biosynthesis pathway or perception. This review aims to explore and dissect the actual mission of BRs in signaling cascades and summarize their positive role with respect to abiotic stress tolerance.

Isolation and Functional Characterization of Soybean BES1/BZR1 Homolog 3-Like 1 (GmBEH3L1) Associated with Dehydration Sensitivity and Brassinosteroid Signaling in Arabidopsis thaliana

Brassinosteroid (BR) is an important steroid hormone that regulates plant development, abscisic acid (ABA) signaling, and responses to abiotic stress. We previously demonstrated that BEH3 (BES1/BZR1 Homolog 3) of Arabidopsis thaliana regulates dehydration and ABA responses by mediating proline metabolism. Furthermore, BEH3 negatively regulates BR-mediated hypocotyl elongation in dark-grown seedlings. However, the roles of BEH3 ortholog genes in the osmotic stress response of plants have remained largely unknown. Here, GmBEH3L1 (Glycine max BEH3-Like 1), a soybean (G. max) ortholog of the BEH3 gene of A. thaliana, was isolated and functionally characterized. GmBEH3L1 is induced by ABA, dehydration, and drought conditions. The GmBEH3L1-overexpressing transgenic lines (GmBEH3L1-OE/beh3) with the beh3 mutant background have ABA- and dehydration-sensitive phenotypes during early seedling growth, implying that GmBEH3L1 is involved in both osmotic stress and ABA sensitivity as a negative regulator in A. thaliana. Consistent with these results, GmBEH3L1-OE/beh3 complemental lines exhibit decreased expression levels of ABA- or dehydration-inducible genes. Under darkness, GmBEH3L1-OE/beh3 complemental lines display a short hypocotyl length compared to the beh3 mutant, indicating that GmBEH3L1 is linked to BR signaling. Together, our data suggest that GmBEH3L1 participates negatively in ABA and dehydration responses through BR signaling.

Physiological and Comparative Transcriptome Analysis Reveals the Mechanism by Which Exogenous 24-Epibrassinolide Application Enhances Drought Resistance in Potato (Solanum tuberosum L.)

Drought stress is a key factor limiting the growth and tuber yield of potatoes (Solanum tuberosum L.). Brassinosteroids (BRs) have been shown to alleviate drought stress in several plant species; however, little is known about the physiological and molecular mechanisms by which BRs enhance drought resistance in potatoes. Here, we characterized changes in the physiology and transcriptome of the tetraploid potato variety ‘Xuanshu-2′ in response to drought stress after 24-epibrassinolide (EBR) pretreatment. The abscisic acid (ABA) content, photosynthetic capacity, and the activities of antioxidant enzymes were increased; the intercellular CO2 concentration, relative conductivity, reactive oxygen species, malondialdehyde, proline, and soluble sugar content were decreased after EBR pretreatment compared with plants under drought stress. Transcriptome analysis revealed 1330 differently expressed genes (DEGs) involved in the response to drought stress after EBR pretreatment. DEGs were enriched in plant hormone signal transduction, starch and sucrose metabolism, circadian rhythm, flavonoid biosynthesis, and carotenoid biosynthesis. DEGs associated with the BR signaling and biosynthesis pathways, as well as ABA metabolic pathways were identified. Our findings provide new insights into the mechanisms by which BRs enhance the drought resistance of potatoes.

ZmBSK1 positively regulates BR-induced H2O2 production via NADPH oxidase and functions in oxidative stress tolerance in maize

Brassinosteroid (BR) has been indicated to induce the production of hydrogen peroxide (H₂O₂) in plants in response to various environmental stimuli. However, it remains largely unknown how BR induces H₂O₂ production. In this study, we found that BR treatment significantly raised the kinase activity of maize (Zea mays L.) brassinosteroid-signaling kinase 1 (ZmBSK1) using the immunoprecipitation kinase assay. ZmBSK1 could modulate the gene expressions and activities of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (EC 1.6.3.1) to modulate BR-induced H₂O₂ production. BR could enhance the interaction between ZmBSK1 and maize calcium/calmodulin-dependent protein kinase (ZmCCaMK), a previously identified substrate of ZmBSK1. The BR-induced phosphorylation and kinase activity of ZmCCaMK are dependent on ZmBSK1. Moreover, we showed that ZmBSK1 regulated the NADPH oxidase gene expression and activity via directly phosphorylating ZmCCaMK. Genetic analysis suggested that ZmBSK1-ZmCCaMK module strengthened plant tolerance to oxidative stress induced by exogenous application of H₂O₂ through improving the activities of antioxidant defense enzyme and alleviating the malondialdehyde (MDA) accumulation and electrolyte leakage rate. In conclusion, these findings provide the new insights of ZmBSK1 functioning in BR-induced H₂O₂ production and the theoretical supports for breeding stress-tolerant crops.

5-Aminolevulinic Acid and 24-Epibrassinolide Improve the Drought Stress Resilience and Productivity of Banana Plants

Plant growth, development, and productivity are adversely affected under drought conditions. Previous findings indicated that 5-aminolevulinic acid (ALA) and 24-epibrassinolide (EBL) play an important role in the plant response to adverse environmental conditions. This study demonstrated the role of ALA and EBL on oxidative stress and photosynthetic capacity of drought-stressed 'Williams' banana grown under the Egyptian semi-arid conditions. Exogenous application of either ALA or EBL at concentrations of 15, 30, and 45 mg·L-1 significantly restored plant photosynthetic activity and increased productivity under reduced irrigation; this was equivalent to 75% of the plant's total water requirements. Both compounds significantly reduced drought-induced oxidative damages by increasing antioxidant enzyme activities (superoxide dismutase 'SOD', catalase 'CAT', and peroxidase 'POD') and preserving chloroplast structure. Lipid peroxidation, electrolyte loss and free non-radical H2O2 formation in the chloroplast were noticeably reduced compared to the control, but chlorophyll content and photosynthetic oxygen evolution were increased. Nutrient uptake, auxin and cytokinin levels were also improved with the reduced abscisic acid levels. The results indicated that ALA and EBL could reduce the accumulation of reactive oxygen species and maintain the stability of the chloroplast membrane structure under drought stress. This study suggests that the use of ALA or EBL at 30 mg·L-1 can promote the growth, productivity and fruit quality of drought-stressed banana plants.

Sexual and Apogamous Species of Woodferns Show Different Protein and Phytohormone Profiles

The gametophyte of ferns reproduces either by sexual or asexual means. In the latter, apogamy represents a peculiar case of apomixis, in which an embryo is formed from somatic cells. A proteomic and physiological approach was applied to the apogamous fern Dryopteris affinis ssp. affinis and its sexual relative D. oreades. The proteomic analysis compared apogamous vs. female gametophytes, whereas the phytohormone study included, in addition to females, three apogamous stages (filamentous, spatulate, and cordate). The proteomic profiles revealed a total of 879 proteins and, after annotation, different regulation was found in 206 proteins of D. affinis and 166 of its sexual counterpart. The proteins upregulated in D. affinis are mostly associated to protein metabolism (including folding, transport, and proteolysis), ribosome biogenesis, gene expression and translation, while in the sexual counterpart, they account largely for starch and sucrose metabolism, generation of energy and photosynthesis. Likewise, ultra-performance liquid chromatography-tandem spectrometry (UHPLC-MS/MS) was used to assess the levels of indol-3-acetic acid (IAA); the cytokinins: 6-benzylaminopurine (BA), trans-Zeatine (Z), trans-Zeatin riboside (ZR), dyhidrozeatine (DHZ), dyhidrozeatin riboside (DHZR), isopentenyl adenine (iP), isopentenyl adenosine (iPR), abscisic acid (ABA), the gibberellins GA₃ and GA₄, salicylic acid (SA), and the brassinosteroids: brassinolide (BL) and castasterone (CS). IAA, the cytokinins Z, ZR, iPR, the gibberellin GA₄, the brassinosteoids castasterone, and ABA accumulated more in the sexual gametophyte than in the apogamous one. When comparing the three apogamous stages, BA and SA peaked in filamentous, GA₃ and BL in spatulate and DHRZ in cordate gametophytes. The results point to the existence of large metabolic differences between apogamous and sexual gametophytes, and invite to consider the fern gametophyte as a good experimental system to deepen our understanding of plant reproduction.

24-epibrassinolide improves differential cadmium tolerance of mung bean roots, stems, and leaves via amending antioxidative systems similar to that of abscisic acid

Cadmium (Cd) pollution has attracted global concern. In the present study, the biochemical mechanisms underlying the amelioration of 24-epibrassinolide (eBL) and abscisic acid (ABA) on Cd tolerance of roots, stems, and leaves in mung bean seedlings were comparatively analyzed. Foliar application of eBL markedly ameliorated the growth of mung bean seedling exposed to 100 μM Cd. eBL alone had no significant effects on the activities of antioxidative enzymes and the contents of glutathione (GSH) and polyphenols in the three organs whereas significantly increased the root, stem, and leaf proline contents on average by 54.9%, 39.9%, and 94.4%, respectively, and leaf malondialdehyde (MDA) content on average by 69.0% compared with the controls. When the plants were exposed to Cd, eBL significantly reversed the Cd-increased root ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities, root polyphenol, proline, and GSH levels, leaf chlorophyll contents, and MDA levels in the three organs. eBL significantly restored the Cd-decreased leaf catalase (CAT) activity and leaf polyphenol levels. These results indicated that eBL played roles in maintaining cellular redox homeostasis and evidently alleviated Cd-caused membrane lipid peroxidation via controlling the activity of antioxidative systems. eBL mediated the differential responses of cellular biochemical processes in the three organs to Cd exposure. Furthermore, a comparative analysis revealed that, under Cd stress, the effects of eBL on the biochemical processes were very similar to those of ABA, suggesting that ABA and eBL improve plant Cd tolerance via some common downstream pathways.

Brassinosteroids as a multidimensional regulator of plant physiological and molecular responses under various environmental stresses

Biotic and abiotic stresses, especially heavy metal toxicity, are becoming a big problem in agriculture, which pose serious threats to crop production. Plant hormones have recently been used to develop stress tolerance in a variety of plants. Brassinosteroids (BRs) are the sixth class of plant steroid hormones, with pleiotropic effects on plants. Exogenous application of BRs to boost plant tolerance mechanisms to various stresses has been a major research focus. Numerous studies have revealed the role of these steroidal hormones in the up-regulation of stress-related resistance genes, as well as their interactions with other metabolic pathways. BRs interact with other phytohormones such as auxin, cytokinin, ethylene, gibberellin, jasmonic acid, abscisic acid, salicylic acid, and polyamines to regulate a variety of physiological and developmental processes in plants. BRs regulate expressions of many BR-inducible genes by activating the brassinazole-resistant 1 (BZR1)/BRI1-EMS suppressor 1 (BES1) complex. Moreover, to improve plant development under a variety of stresses, BRs regulate antioxidant enzyme activity, chlorophyll concentration, photosynthetic capability, and glucose metabolism. This review will provide insights into the mechanistic role and actions of brassinosteroids in plants in response to various stresses.

Role of jasmonic acid in plants: the molecular point of view

Recent updates in JA biosynthesis, signaling pathways and the crosstalk between JA and others phytohormones in relation with plant responses to different stresses. In plants, the roles of phytohormone jasmonic acid (JA), amino acid conjugate (e.g., JA-Ile) and their derivative emerged in last decades as crucial signaling compounds implicated in stress defense and development in plants. JA has raised a great interest, and the number of researches on JA has increased rapidly highlighting the importance of this phytohormone in plant life. First, JA was considered as a stress hormone implicated in plant response to biotic stress (pathogens and herbivores) which confers resistance to biotrophic and hemibiotrophic pathogens contrarily to salicylic acid (SA) which is implicated in plant response to necrotrophic pathogens. JA is also implicated in plant responses to abiotic stress (such as soil salinity, wounding and UV). Moreover, some researchers have recently revealed that JA controls several physiological processes like root growth, growth of reproductive organs and, finally, plant senescence. JA is also involved in the biosynthesis of various metabolites (e.g., phytoalexins and terpenoids). In plants, JA signaling pathways are well studied in few plants essentially Arabidopsis thaliana, Nicotiana benthamiana, and Oryza sativa L. confirming the crucial role of this hormone in plants. In this review, we highlight the last foundlings about JA biosynthesis, JA signaling pathways and its implication in plant maturation and response to environmental constraints.

The first draft genome of Picrorhiza kurrooa, an endangered medicinal herb from Himalayas

Picrorhiza kurrooa is an endangered medicinal herb which is distributed across the Himalayan region at an altitude between 3000–5000 m above mean sea level. The medicinal properties of P. kurrooa are attributed to monoterpenoid picrosides present in leaf, rhizome and root of the plant. However, no genomic information is currently available for P. kurrooa, which limits our understanding about its molecular systems and associated responses. The present study brings the first assembled draft genome of P. kurrooa by using 227 Gb of raw data generated by Illumina and PacBio RS II sequencing platforms. The assembled genome has a size of n = ~ 1.7 Gb with 12,924 scaffolds. Four pronged assembly quality validations studies, including experimentally reported ESTs mapping and directed sequencing of the assembled contigs, confirmed high reliability of the assembly. About 76% of the genome is covered by complex repeats alone. Annotation revealed 24,798 protein coding and 9789 non-coding genes. Using the assembled genome, a total of 710 miRNAs were discovered, many of which were found responsible for molecular response against temperature changes. The miRNAs and targets were validated experimentally. The availability of draft genome sequence will aid in genetic improvement and conservation of P. kurrooa. Also, this study provided an efficient approach for assembling complex genomes while dealing with repeats when regular assemblers failed to progress due to repeats.

Contribution of strigolactone in plant physiology, hormonal interaction and abiotic stresses

Strigolactones (SLs) are carotenoid-derived molecules, which regulate various developmental and adaptation processes in plants. These are engaged in different aspects of growth such as development of root, leaf senescence, shoot branching, etc. Plants grown under nutrient-deficient conditions enhance SL production that facilitates root architecture and symbiosis of arbuscular mycorrhizal fungi, as a result increases nutrient uptake. The crosstalk of SLs with other phytohormones such as auxin, abscisic acid, cytokinin and gibberellins, in response to abiotic stresses indicates that SLs actively contribute to the regulatory systems of plant stress adaptation. In response to different environmental circumstances such as salinity, drought, heat, cold, heavy metals and nutrient deprivation, these SLs get accumulated in plant tissues. Strigolactones regulate multiple hormonal responsive pathways, which aids plants to surmount stressful environmental constraints as well as reduce negative impact on overall productivity of crops. The external application of SL analog GR24 for its higher bioaccumulation can be one of the possible approaches for establishing various abiotic stress tolerances in plants.

Consequences of LED Lights on Root Morphological Traits and Compounds Accumulation in Sarcandra glabra Seedlings

This study evaluated the effects of different light spectra (white light; WL, blue light; BL and red light; RL) on the root morphological traits and metabolites accumulation and biosynthesis in Sarcandra glabra. We performed transcriptomic and metabolomic profiling by RNA-seq and ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS), respectively. When morphological features were compared to WL, BL substantially increased under-ground fresh weight, root length, root surface area, and root volume, while RL inhibited these indices. A total of 433 metabolites were identified, of which 40, 18, and 68 compounds differentially accumulated in roots under WL (WG) vs. roots under BL (BG), WG vs. roots under RL (RG), and RG vs. BG, respectively. In addition, the contents of sinapyl alcohol, sinapic acid, fraxetin, and 6-methylcoumarin decreased significantly in BG and RG. In contrast, chlorogenic acid, rosmarinyl glucoside, quercitrin and quercetin were increased considerably in BG. Furthermore, the contents of eight terpenoids compounds significantly reduced in BG. Following transcriptomic profiling, several key genes related to biosynthesis of phenylpropanoid-derived and terpenoids metabolites were differentially expressed, such as caffeic acid 3-O-methyltransferase) (COMT), hydroxycinnamoyl-CoA shikimate hydroxycinnamoyl transferase (HCT), O-methyltransferase (OMT), and 1-deoxy-D-xylulose-5-phosphate synthetase (DXS). In summary, our findings showed that BL was suitable for growth and accumulation of bioactive metabolites in root tissue of S. glabra. Exposure to a higher ratio of BL might have the potential to improve the production and quality of S. glabra seedlings, but this needs to be confirmed further.

Two ATAF transcription factors ANAC102 and ATAF1 contribute to the suppression of cytochrome P450-mediated brassinosteroid catabolism in Arabidopsis

PHYB ACTIVATION TAGGED SUPPRESSOR 1 (BAS1) and SUPPRESSOR OF PHYB-4 7 (SOB7) are two cytochrome P450 enzymes that inactivate brassinosteroids (BRs) in Arabidopsis. The NAC transcription factor (TF) ATAF2 (ANAC081) and the core circadian clock regulator CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) both suppress the expression of BAS1 and SOB7 via direct promoter binding. Additionally, BRs cause feedback suppression on ATAF2 expression. Here, we report that two ATAF-subgroup TFs, ANAC102 and ATAF1 (ANAC002), also contribute to the transcriptional suppression of BAS1 and SOB7. ANAC102 and ATAF1 gene-knockout mutants exhibit elevated expression of both BAS1 and SOB7, expanded tissue-level accumulation of their protein products and reduced hypocotyl growth in response to exogenous BR treatments. Similar to ATAF2, both ANAC102 and ATAF1 are transcriptionally suppressed by BRs and white light. Neither BAS1 nor SOB7 expression is further elevated in ATAF double or triple mutants, suggesting that the suppression effect of these three ATAFs is not additive. In addition, ATAF single, double, and triple mutants have similar levels of BR responsiveness with regard to hypocotyl elongation. ATAF2, ANAC102, ATAF1, and CCA1 physically interact with itself and each other, suggesting that they may coordinately suppress BAS1 and SOB7 expression via protein-protein interactions. Despite the absence of CCA1-binding elements in their promoters, ANAC102 and ATAF1 have similar transcript circadian oscillation patterns as that of CCA1, suggesting that these two ATAF genes may be indirectly regulated by the circadian clock.

Genome-wide expression and network analyses of mutants in key brassinosteroid signaling genes

BACKGROUND

Brassinosteroid (BR) signaling regulates plant growth and development in concert with other signaling pathways. Although many genes have been identified that play a role in BR signaling, the biological and functional consequences of disrupting those key BR genes still require detailed investigation.

RESULTS

Here we performed phenotypic and transcriptomic comparisons of A. thaliana lines carrying a loss-of-function mutation in BRI1 gene, bri1-5, that exhibits a dwarf phenotype and its three activation-tag suppressor lines that were able to partially revert the bri1-5 mutant phenotype to a WS2 phenotype, namely bri1-5/bri1-1D, bri1-5/brs1-1D, and bri1-5/bak1-1D. From the three investigated bri1-5 suppressors, bri1-5/bak1-1D was the most effective suppressor at the transcriptional level. All three bri1-5 suppressors showed altered expression of the genes in the abscisic acid (ABA signaling) pathway, indicating that ABA likely contributes to the partial recovery of the wild-type phenotype in these bri1-5 suppressors. Network analysis revealed crosstalk between BR and other phytohormone signaling pathways, suggesting that interference with one hormone signaling pathway affects other hormone signaling pathways. In addition, differential expression analysis suggested the existence of a strong negative feedback from BR signaling on BR biosynthesis and also predicted that BRS1, rather than being directly involved in signaling, might be responsible for providing an optimal environment for the interaction between BRI1 and its ligand.

CONCLUSIONS

Our study provides insights into the molecular mechanisms and functions of key brassinosteroid (BR) signaling genes, especially BRS1.

24-Epibrasinolide Modulates the Vase Life of Lisianthus Cut Flowers by Modulating ACC Oxidase Enzyme Activity and Physiological Responses

Ethylene is the most important factor playing roles in senescence and deterioration of harvested crops including cut flowers. Brassinosteroids (BRs), as natural phytohormones, have been reported to differently modulate ethylene production and related senescence processes in different crops. This study was carried out to determine the effects of different levels of 24-epibrassinolide (EBL) on ACC oxidase enzyme activity, the final enzyme in ethylene biosynthesis pathway, vase life, and senescence rate in lisianthus cut flowers. Harvested flowers were treated with EBL (at 0, 3, 6, and 9 µmol/L) and kept at 25 °C for 15 days. The ACC oxidase activity, water absorption, malondialdehyde (MDA) production and vase solution absorption rates, chlorophyll and anthocyanin contents, and the vase life of the flowers were evaluated during and at the end of storage. EBL at 3 µmol/L significantly (p ≤ 0.01) enhanced the flower vase life by decreasing the ACC oxidase activity, MDA production and senescence rates, and enhancing chlorophyll and anthocyanin biosynthesis and accumulation, relative water content, and vase solution absorption rates. By increasing the concentration, EBL negatively affected the flower vase life and postharvest quality probably via enhancing the ACC oxidase enzyme activity and subsequent ethylene production. EBL at 6 and 9 µmol/L and in a concentration dependent manner, enhanced the ACC oxidase activity and MDA production rate and decreased chlorophyll and anthocyanin accumulation and water absorption rate. The results indicate that the effects of brassinosteroids on ethylene production and physiology of lisianthus cut flowers is highly dose dependent.

Exogenous EBR Ameliorates Endogenous Hormone Contents in Tomato Species under Low-Temperature Stress

Low-temperature stress is a type of abiotic stress that limits plant growth and production in both subtropical and tropical climate conditions. In the current study, the effects of 24-epi-brassinolide (EBR) as analogs of brassinosteroids (BRs) were investigated, in terms of hormone content, antioxidant enzyme activity, and transcription of several cold-responsive genes, under low-temperature stress (9 °C) in two different tomato species (cold-sensitive and cold-tolerant species). Results indicated that the treatment with exogenous EBR increases the content of gibberellic acid (GA3) and indole-3-acetic acid (IAA), whose accumulation is reduced by low temperatures in cold-sensitive species. Furthermore, the combination or contribution of BR and abscisic acid (ABA) as a synergetic interaction was recognized between BR and ABA in response to low temperatures. The content of malondialdehyde (MDA) and proline was significantly increased in both species, in response to low-temperature stress; however, EBR treatment did not affect the MDA and proline content. Moreover, in the present study, the effect of EBR application was different in the tomato species under low-temperature stress, which increased the catalase (CAT) activity in the cold-tolerant species and increased the glutathione peroxidase (GPX) activity in the cold-sensitive species. Furthermore, expression levels of cold-responsive genes were influenced by low-temperature stress and EBR treatment. Overall, our findings revealed that a low temperature causes oxidative stress while EBR treatment may decrease the reactive oxygen species (ROS) damage into increasing antioxidant enzymes, and improve the growth rate of the tomato by affecting auxin and gibberellin content. This study provides insight into the mechanism by which BRs regulate stress-dependent processes in tomatoes, and provides a theoretical basis for promoting cold resistance of the tomato.

Current understanding of the interplays between host hormones and plant viral infections

Phytohormones mediate plant development and responses to stresses caused by biotic agents or abiotic factors. The functions of phytohormones in responses to viral infection have been intensively studied, and the emerging picture of complex mechanisms provides insights into the roles that phytohormones play in defense regulation as a whole. These hormone signaling pathways are not simple linear or isolated cascades, but exhibit crosstalk with each other. Here, we summarized the current understanding of recent advances for the classical defense hormones salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) and also the roles of abscisic acid (ABA), auxin, gibberellic acid (GA), cytokinins (CKs), and brassinosteroids (BRs) in modulating plant–virus interactions.

BES1/BZR1 Homolog 3 cooperates with E3 ligase AtRZF1 to regulate osmotic stress and brassinosteroid responses in Arabidopsis

Proline (Pro) metabolism plays important roles in protein synthesis, redox balance, and abiotic stress response. However, it is not known if cross-talk occurs between proline and brassinosteroid (BR) signaling pathways. Here, an Arabidopsis intergenic enhancer double mutant, namely proline content alterative 41 (pca41), was generated by inserting a T-DNA tag in the Arabidopsis thaliana ring zinc finger 1 (atrzf1 ) mutant background. pca41 had a T-DNA inserted at the site of the gene encoding BES1/BZR1 Homolog 3 (BEH3). pca41 has a drought-insensitive phenotype that is stronger than atrzf1 under osmotic stress, including high Pro accumulation and decreased amounts of reactive oxygen species. Analysis of physiological, genetic, and molecular networks revealed that negative regulation of BEH3 during abiotic stress was linked to the BR signaling pathway. Our data also suggest that AtRZF1, an E3 ubiquitin ligase, might control osmotic stress, abscisic acid, and BR responses in a BEH3-dependent manner. Under darkness, pca41 displays a long hypocotyl phenotype, which is similar to atrzf1 and beh3, suggesting that BEH3 acts in the same pathway as AtRZF1. Overexpression of BEH3 results in an osmotic stress-sensitive phenotype, which is reversed by exogenous BR application. Taken together, our results indicate that AtRZF1 and BEH3 may play important roles in the osmotic stress response via ubiquitination and BR signaling.

Exogenous Application of Brassinosteroid 24-Norcholane 22(S)-23-Dihydroxy Type Analogs to Enhance Water Deficit Stress Tolerance in Arabidopsis thaliana

Brassinosteroids (BRs) are plant hormones that play an essential role in plant development and have the ability to protect plants against various environmental stresses, such as low and high temperature, drought, heat, salinity, heavy metal toxicity, and pesticides. Mitigation of stress effects are produced through independent mechanisms or by interaction with other important phytohormones. However, there are few studies in which this property has been reported for BRs analogs. Thus, in this work, the enhancement of drought stress tolerance of A. thaliana was assessed for a series of 2-deoxybrassinosteroid analogs. In addition, the growth-promoting activity in the Rice Lamina Inclination Test (RLIT) was also evaluated. The results show that analog 1 exhibits similar growth activity as brassinolide (BL; used as positive control) in the RLIT bioassay. Interestingly, both compounds increase their activities by a factor of 1.2–1.5 when they are incorporated to polymer micelles formed by Pluronic F-127. On the other hand, tolerance to water deficit stress of Arabidopsis thaliana seedlings was evaluated by determining survival rate and dry weight of seedlings after the recovery period. In both cases, the effect of analog 1 is higher than that exhibited by BL. Additionally, the expression of a subset of drought stress marker genes was evaluated in presence and absence of exogenous applied BRs. Results obtained by qRT-PCR analysis, indicate that transcriptional changes of AtDREBD2A and AtNCED3 genes were more significant in A. thaliana treated with analog 1 in homogeneous solution than in that treated with BL. These changes suggest the activation of alternative pathway in response to water stress deficit. Thus, exogenous application of BRs synthetic analogs could be a potential tool for improvement of crop production under stress conditions.

Jasmonates, Ethylene and Brassinosteroids Control Adventitious and Lateral Rooting as Stress Avoidance Responses to Heavy Metals and Metalloids

Developmental and environmental signaling networks often converge during plant growth in response to changing conditions. Stress-induced hormones, such as jasmonates (JAs), can influence growth by crosstalk with other signals like brassinosteroids (BRs) and ethylene (ET). Nevertheless, it is unclear how avoidance of an abiotic stress triggers local changes in development as a response. It is known that stress hormones like JAs/ET and BRs can regulate the division rate of cells from the first asymmetric cell divisions (ACDs) in meristems, suggesting that stem cell activation may take part in developmental changes as a stress-avoidance-induced response. The root system is a prime responder to stress conditions in soil. Together with the primary root and lateral roots (LRs), adventitious roots (ARs) are necessary for survival in numerous plant species. AR and LR formation is affected by soil pollution, causing substantial root architecture changes by either depressing or enhancing rooting as a stress avoidance/survival response. Here, a detailed overview of the crosstalk between JAs, ET, BRs, and the stress mediator nitric oxide (NO) in auxin-induced AR and LR formation, with/without cadmium and arsenic, is presented. Interactions essential in achieving a balance between growth and adaptation to Cd and As soil pollution to ensure survival are reviewed here in the model species Arabidopsis and rice.

How Hormones and MADS-Box Transcription Factors Are Involved in Controlling Fruit Set and Parthenocarpy in Tomato

Fruit set is the earliest phase of fruit growth and represents the onset of ovary growth after successful fertilization. In parthenocarpy, fruit formation is less affected by environmental factors because it occurs in the absence of pollination and fertilization, making parthenocarpy a highly desired agronomic trait. Elucidating the genetic program controlling parthenocarpy, and more generally fruit set, may have important implications in agriculture, considering the need for crops to be adaptable to climate changes. Several phytohormones play an important role in the transition from flower to fruit. Further complexity emerges from functional analysis of floral homeotic genes. Some homeotic MADS-box genes are implicated in fruit growth and development, displaying an expression pattern commonly observed for ovary growth repressors. Here, we provide an overview of recent discoveries on the molecular regulatory gene network underlying fruit set in tomato, the model organism for fleshy fruit development due to the many genetic and genomic resources available. We describe how the genetic modification of components of this network can cause parthenocarpy, discussing the contribution of hormonal signals and MADS-box transcription factors.

Foliar Application of 24-Epibrassinolide Improves Growth, Ascorbate-Glutathione Cycle, and Glyoxalase System in Brown Mustard (Brassica juncea (L.) Czern.) under Cadmium Toxicity

Cadmium (Cd) metal toxicity is a crucial ecological matter that requires immediate efforts to mitigate it. Brassica juncea plants were exposed to Cd (0 and 200 µM as CdSO₄) and foliar application of 24-Epibrassinolide (EBR) (0, 10⁻⁷ and 10⁻⁵ M). The toxic effect of Cd was evident in terms of declined growth and biomass yield, lowered levels of pigment content and chlorophyll fluorescence, and reduction in gas exchange attributes. The levels of proline and glycinebetaine increased in response to Cd treatment. There was an imperative rise in the contents of H₂O₂ and malondialdehyde as well as electrolyte leakage in the Cd-stressed plants. With the application of EBR, there was a significant replenishment in growth attributes and photosynthetic efficacy. The contents of ROS (reactive oxygen species) and malondialdehyde as well as electrolyte leakage were reduced by the hormone supplementation. Enhancement in the contents of glutathione and ascorbic acid, and the activities of enzymes of the antioxidative defense system and glyoxalase system was recorded in response to Cd as well as hormone treatment. The in situ levels of Cd in roots and shoot were augmented in response to Cd treatment, but were found to be lowered by the EBR application.

Brassinosteroid Regulates 3-Hydroxy-3-methylglutaryl CoA Reductase to Promote Grape Fruit Development

Brassinosteroids (BRs) are known to regulate plant growth and development. However, only little is known about their mechanism in the regulation of berry development in grapes. This study demonstrates that BR treatment enhances the accumulation of fruit sugar components, reduces the content of organic acids (e.g., tartaric acid), promotes coloration, and increases the anthocyanin content in grape berries at the onset of the veraison, half veraison, and full veraison stages at the rate of 0.0998, 0.0560, and 0.0281 mg·g^-1_, respectively. In addition, BR treatment was also found to accelerate the biosynthesis of terpenoid aroma components, such as α-pinene, d-limonene, and γ-terpinene, which influence the aromatic composition of grapes. BRs can negatively regulate the expression of VvHMGR, a key gene involved in the mevalonate (MVA) pathway, and reduce the activity of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR). Inhibiting the expression of HMGR promoted the accumulation of anthocyanins and fruit coloration. Meanwhile, after the inhibition, the contents of auxin indole-3-acetic acid (IAA), abscisic acid (ABA), and brassinosteroid (BR) increased, while gibberellin (GA₃) and zeatin riboside (ZR) decreased, and its aromatic composition also changed. Therefore, it may be concluded that BRs inhibited HMGR activity and cooperated with VvHMGR to regulate the formation of color, aroma, and other quality characteristics in fruits.

Insights into Metabolic Reactions of Semi-Dwarf, Barley Brassinosteroid Mutants to Drought

The roles of endogenous brassinosteroids (BRs) in the modulation of reaction to drought and genetic regulation of this process are still obscure. In this study, a multidirectional analysis was performed on semi-dwarf barley (Hordeum vulgare) Near-Isogenic Lines (NILs) and the reference cultivar “Bowman” to get insights into various aspects of metabolic reaction to drought. The NILs are defective in BR biosynthesis or signaling and displayed an enhanced tolerance to drought. The BR metabolism perturbations affected the glucose and fructose accumulation under the control and stress conditions. The BR metabolism abnormalities negatively affected the sucrose accumulation as well. However, during drought, the BR-deficient NILs accumulated higher contents of sucrose than the “Bowman” cultivar. Under the control conditions, accumulation of transcripts encoding antioxidant enzymes ascorbate peroxidase (HvAPX) and superoxide dismutase (HvSOD) was BR-dependent. However, during drought, the accumulation of HvAPX transcript was BR-dependent, whereas accumulations of transcripts encoding catalase (HvCAT) and HvSOD were not affected by the BR metabolism perturbations. The obtained results reveal a significant role of BRs in regulation of the HvAPX and HvCAT enzymatic activities under control conditions and the HvAPX and HvSOD activities during physiological reactions to drought.

Expression profiles of four BES1/BZR1 homologous genes encoding bHLH transcription factors in Arabidopsis

Arabidopsis bHLH-type transcription factors-BRASSINOSTEROID INSENSITIVE 1-EMS-SUPPRESSOR 1 (BES1) and BRASSINAZOLE RESISTANT 1 (BZR1)-play key roles in brassinosteroid (BR) signaling. By contrast, the functions of the other four BES1/BZR1 homologs (BEH1-4) remain unknown. Here, we describe the detailed expression profiles of the BES1/BZR1 family genes. Their expressions were distinct regarding growth-stage dependence and organ specificity but exhibited some overlaps as well. Furthermore, their mRNA levels mostly remained unchanged responding to seven non-BR phytohormones. However, BEH1 and BEH2 were downregulated by brassinolide, suggesting a close association with the BR function. Additionally, BEH4 was ubiquitously expressed throughout the life of the plant but displayed some expression preference. For instance, BEH4 expression was limited to guard cells and the adjacent pavement cells in the leaf epidermis and was induced during growth progression in very young seedlings, suggesting that BEH4 is specifically regulated in certain contexts, although it is almost constitutively controlled.

Transgenic Breeding Approaches for Improving Abiotic Stress Tolerance: Recent Progress and Future Perspectives

The recent rapid climate changes and increasing global population have led to an increased incidence of abiotic stress and decreased crop productivity. Environmental stresses, such as temperature, drought, nutrient deficiency, salinity, and heavy metal stresses, are major challenges for agriculture, and they lead to a significant reduction in crop growth and productivity. Abiotic stress is a very complex phenomenon, involving a variety of physiological and biochemical changes in plant cells. Plants exposed to abiotic stress exhibit enhanced levels of ROS (reactive oxygen species), which are highly reactive and toxic and affect the biosynthesis of chlorophyll, photosynthetic capacity, and carbohydrate, protein, lipid, and antioxidant enzyme activities. Transgenic breeding offers a suitable alternative to conventional breeding to achieve plant genetic improvements. Over the last two decades, genetic engineering/transgenic breeding techniques demonstrated remarkable developments in manipulations of the genes for the induction of desired characteristics into transgenic plants. Transgenic approaches provide us with access to identify the candidate genes, miRNAs, and transcription factors (TFs) that are involved in specific plant processes, thus enabling an integrated knowledge of the molecular and physiological mechanisms influencing the plant tolerance and productivity. The accuracy and precision of this phenomenon assures great success in the future of plant improvements. Hence, transgenic breeding has proven to be a promising tool for abiotic stress improvement in crops. This review focuses on the potential and successful applications, recent progress, and future perspectives of transgenic breeding for improving abiotic stress tolerance and productivity in plants.

Functions of Jasmonic Acid in Plant Regulation and Response to Abiotic Stress

Jasmonic acid (JA) is an endogenous growth-regulating substance, initially identified as a stress-related hormone in higher plants. Similarly, the exogenous application of JA also has a regulatory effect on plants. Abiotic stress often causes large-scale plant damage. In this review, we focus on the JA signaling pathways in response to abiotic stresses, including cold, drought, salinity, heavy metals, and light. On the other hand, JA does not play an independent regulatory role, but works in a complex signal network with other phytohormone signaling pathways. In this review, we will discuss transcription factors and genes involved in the regulation of the JA signaling pathway in response to abiotic stress. In this process, the JAZ-MYC module plays a central role in the JA signaling pathway through integration of regulatory transcription factors and related genes. Simultaneously, JA has synergistic and antagonistic effects with abscisic acid (ABA), ethylene (ET), salicylic acid (SA), and other plant hormones in the process of resisting environmental stress.

An S-domain receptor-like kinase, OsESG1, regulates early crown root development and drought resistance in rice

Plant receptor-like kinase (RLKs) are serine/threonine protein kinases that play fundamental roles in development, innate immunity, and abiotic stress response. Here, we identified an S-domain receptor-like kinase OsESG1 from rice (Oryza sativa), and identified its involvement in early crown root (CR) development and drought response. The OsESG1 kinase domain possessed auto-phosphorylation activity and was able to phosphorylate MBP and His proteins. OsESG1 was expressed ubiquitously in all tissues that were examined, with relatively higher expression in the embryo. And it could be induced to express by treating with PEG, NaCl and ABA. Transgenic plants carrying anti-sense (AS) OsESG1 were generated by knockdown of OsESG1 expression. At the early seedling stage, AS lines had fewer CRs and shorter shoot compared with wild type (WT) plants. IAA flux and the genes' expressions of the auxin responsive and efflux carrier were infected in the AS lines. These results indicated that auxin signaling and polar auxin transport (PAT) were disrupted. The AS lines were more sensitive to osmotic stress compared to WT, and showed excessive accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA), lower activities of antioxidant enzymes, and impaired expressions of stress-related genes under PEG treatment. Results above suggested that OsESG1 may regulate CR initiation and development by controlling auxin response and distribution, and participate in stress response by regulating the activities of antioxidants and expressions of stress-regulated genes.

Mechanisms Regulating the Dynamics of Photosynthesis Under Abiotic Stresses

Photosynthesis sustains plant life on earth and is indispensable for plant growth and development. Factors such as unfavorable environmental conditions, stress regulatory networks, and plant biochemical processes limits the photosynthetic efficiency of plants and thereby threaten food security worldwide. Although numerous physiological approaches have been used to assess the performance of key photosynthetic components and their stress responses, though, these approaches are not extensive enough and do not favor strategic improvement of photosynthesis under abiotic stresses. The decline in photosynthetic capacity of plants due to these stresses is directly associated with reduction in yield. Therefore, a detailed information of the plant responses and better understanding of the photosynthetic machinery could help in developing new crop plants with higher yield even under stressed environments. Interestingly, cracking of signaling and metabolic pathways, identification of some key regulatory elements, characterization of potential genes, and phytohormone responses to abiotic factors have advanced our knowledge related to photosynthesis. However, our understanding of dynamic modulation of photosynthesis under dramatically fluctuating natural environments remains limited. Here, we provide a detailed overview of the research conducted on photosynthesis to date, and highlight the abiotic stress factors (heat, salinity, drought, high light, and heavy metal) that limit the performance of the photosynthetic machinery. Further, we reviewed the role of transcription factor genes and various enzymes involved in the process of photosynthesis under abiotic stresses. Finally, we discussed the recent progress in the field of biodegradable compounds, such as chitosan and humic acid, and the effect of melatonin (bio-stimulant) on photosynthetic activity. Based on our gathered researched data set, the logical concept of photosynthetic regulation under abiotic stresses along with improvement strategies will expand and surely accelerate the development of stress tolerance mechanisms, wider adaptability, higher survival rate, and yield potential of plant species.

Comparing and Contrasting the Multiple Roles of Butenolide Plant Growth Regulators: Strigolactones and Karrikins in Plant Development and Adaptation to Abiotic Stresses

Strigolactones (SLs) and karrikins (KARs) are both butenolide molecules that play essential roles in plant growth and development. SLs are phytohormones, with SLs having known functions within the plant they are produced in, while KARs are found in smoke emitted from burning plant matter and affect seeds and seedlings in areas of wildfire. It has been suggested that SL and KAR signaling may share similar mechanisms. The α/β hydrolases DWARF14 (D14) and KARRIKIN INSENSITIVE 2 (KAI2), which act as receptors of SL and KAR, respectively, both interact with the F-box protein MORE AXILLARY GROWTH 2 (MAX2) in order to target SUPPRESSOR OF MAX2 1 (SMAX1)-LIKE/D53 family members for degradation via the 26S proteasome. Recent reports suggest that SLs and/or KARs are also involved in regulating plant responses and adaptation to various abiotic stresses, particularly nutrient deficiency, drought, salinity, and chilling. There is also crosstalk with other hormone signaling pathways, including auxin, gibberellic acid (GA), abscisic acid (ABA), cytokinin (CK), and ethylene (ET), under normal and abiotic stress conditions. This review briefly covers the biosynthetic and signaling pathways of SLs and KARs, compares their functions in plant growth and development, and reviews the effects of any crosstalk between SLs or KARs and other plant hormones at various stages of plant development. We also focus on the distinct responses, adaptations, and regulatory mechanisms related to SLs and/or KARs in response to various abiotic stresses. The review closes with discussion on ways to gain additional insights into the SL and KAR pathways and the crosstalk between these related phytohormones.

Brassinosteroids Induce Strong, Dose-Dependent Inhibition of Etiolated Pea Seedling Growth Correlated with Ethylene Production

We have recently discovered that brassinosteroids (BRs) can inhibit the growth of etiolated pea seedlings dose-dependently in a similar manner to the 'triple response' induced by ethylene. We demonstrate here that the growth inhibition of etiolated pea shoots strongly correlates with increases in ethylene production, which also responds dose-dependently to applied BRs. We assessed the biological activities of two natural BRs on pea seedlings, which are excellent material as they grow rapidly, and respond both linearly and uni-phasically to applied BRs. We then compared the BRs' inhibitory effects on growth, and induction of ethylene and ACC (1-aminocyclopropane-1-carboxylic acid) production, to those of representatives of other phytohormone classes (cytokinins, auxins, and gibberellins). Auxin induced ca. 50-fold weaker responses in etiolated pea seedlings than brassinolide, and the other phytohormones induced much weaker (or opposite) responses. Following the optimization of conditions for determining ethylene production after BR treatment, we found a positive correlation between BR bioactivity and ethylene production. Finally, we optimized conditions for pea growth responses and developed a new, highly sensitive, and convenient bioassay for BR activity.