Cytokinins: metabolism and function in plant adaptation to environmental stresses

Dynamic metabolite QTL analyses provide novel biochemical insights into kernel development and nutritional quality improvement in common wheat

Despite recent advances in crop metabolomics, the genetic control and molecular basis of the wheat kernel metabolome at different developmental stages remain largely unknown. Here, we performed widely targeted metabolite profiling of kernels from three developmental stages (grain-filling kernels [FKs], mature kernels [MKs], and germinating kernels [GKs]) using a population of 159 recombinant inbred lines. We detected 625 annotated metabolites and mapped 3173, 3143, and 2644 metabolite quantitative trait loci (mQTLs) in FKs, MKs, and GKs, respectively. Only 52 mQTLs were mapped at all three stages, indicating the high stage specificity of the wheat kernel metabolome. Four candidate genes were functionally validated by in vitro enzymatic reactions and/or transgenic approaches in wheat, three of which mediated the tricin metabolic pathway. Metabolite flux efficiencies within the tricin pathway were evaluated, and superior candidate haplotypes were identified, comprehensively delineating the tricin metabolism pathway in wheat. Finally, additional wheat metabolic pathways were re-constructed by updating them to incorporate the 177 candidate genes identified in this study. Our work provides new information on variations in the wheat kernel metabolome and important molecular resources for improvement of wheat nutritional quality.

The E3 ligase TaGW2 mediates transcription factor TaARR12 degradation to promote drought resistance in wheat

Drought stress limits crop yield, but the molecular modulators and their mechanisms underlying the trade-off between drought resistance and crop growth and development remain elusive. Here, a grain width and weight2 (GW2)-like really interesting new gene finger E3 ligase, TaGW2, was identified as a pivotal regulator of both kernel development and drought responses in wheat (Triticum aestivum). TaGW2 overexpression enhances drought resistance but leads to yield drag under full irrigation conditions. In contrast, TaGW2 knockdown or knockout attenuates drought resistance but remarkably increases kernel size and weight. Furthermore, TaGW2 directly interacts with and ubiquitinates the type-B Arabidopsis response regulator TaARR12, promoting its degradation via the 26S proteasome. Analysis of TaARR12 overexpression and knockdown lines indicated that TaARR12 represses the drought response but does not influence grain yield in wheat. Further DNA affinity purification sequencing combined with transcriptome analysis revealed that TaARR12 downregulates stress-responsive genes, especially group-A basic leucine zipper (bZIP) genes, resulting in impaired drought resistance. Notably, TaARR12 knockdown in the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated nuclease 9 (Cas9)-mediated tagw2 knockout mutant leads to significantly higher drought resistance and grain yield compared to wild-type plants. Collectively, these findings show that the TaGW2-TaARR12 regulatory module is essential for drought responses, providing a strategy for improving stress resistance in high-yield wheat varieties.

Assessing HCH isomer uptake in Alnus glutinosa: implications for phytoremediation and microbial response

Although the pesticide hexachlorocyclohexane (HCH) and its isomers have long been banned, their presence in the environment is still reported worldwide. In this study, we investigated the bioaccumulation potential of α, β, and δ hexachlorocyclohexane (HCH) isomers in black alder saplings (Alnus glutinosa) to assess their environmental impact. Each isomer, at a concentration of 50 mg/kg, was individually mixed with soil, and triplicate setups, including a control without HCH, were monitored for three months with access to water. Gas chromatography-mass spectrometry revealed the highest concentrations of HCH isomers in roots, decreasing towards branches and leaves, with δ-HCH exhibiting the highest uptake (roots-14.7 µg/g, trunk-7.2 µg/g, branches-1.53 µg/g, leaves-1.88 µg/g). Interestingly, α-HCH was detected in high concentrations in β-HCH polluted soil. Phytohormone analysis indicated altered cytokinin, jasmonate, abscisate, and gibberellin levels in A. glutinosa in response to HCH contamination. In addition, amplicon 16S rRNA sequencing was used to study the rhizosphere and soil microbial community. While rhizosphere microbial populations were generally similar in all HCH isomer samples, Pseudomonas spp. decreased across all HCH-amended samples, and Tomentella dominated in β-HCH and control rhizosphere samples but was lowest in δ-HCH samples.

Comprehensive effects of thiamethoxam from contaminated soil on lettuce growth and metabolism

The second-generation neonicotinoid thiamethoxam, is prevalent in soils because of its extensive application and persistence. However, the comprehensive effects of thiamethoxam residue in soils on cultivated plants are still poorly understood. This study examined variations of growth state, physiological parameters, antioxidant activity, and metabolites in lettuce after thiamethoxam exposure; the removal effects of different washing procedures were also investigated. The results indicated that thiamethoxam in soils significantly increased the fresh weight, seedling height and chlorophyll content in lettuce, and also altered its lipid, carbohydrate, nucleotide and amino acids composition based on untargeted metabolomics. KEGG pathway analysis uncovered a disruption of lipid pathways in lettuce exposed to both low and high concentrations of thiamethoxam treatments. In addition, the terminal residues of thiamethoxam in lettuce were below the corresponding maximum residue limits stipulated for China. The thiamethoxam removal rates achieved by common washing procedures in lettuce ranged from 26.9% to 42.6%. This study thus promotes the understanding of the potential food safety risk caused by residual thiamethoxam in soils.

Comprehensive metabolome and growth effects of thiamethoxam uptake and accumulation from soil on pak choi

Extensive use of the neonicotinoid thiamethoxam (TMX) results in its deposition in soil, which can then be absorbed and translocated in vegetables. Here we analyzed the comprehensive effects of TMX on pak choi. The TMX translocation factor (TF) was 0.37-11.65 and 0.46-39.75 for low and high treatments over 28 d, respectively, indicating its ready ability to move from the roots to the leaves of these plants. This uptake was associated with significant decrease in the fresh weight, and increase in vitamin C (VC), soluble sugars and soluble solid of pak choi. A metabolomic analysis revealed that fatty acids and purine nucleosides significantly decreased, and flavonoids and carbohydrates increased in the presence of TMX. TMX exposure thus influenced plant growth and disrupted the carbohydrate and lipid metabolism pathways. Our study raises concerns for food safety risk associated with TMX-contaminated soil.

Genome-Wide Studies of FH Family Members in Soybean (Glycine max) and Their Responses under Abiotic Stresses

Formins or formin homology 2 (FH2) proteins, evolutionarily conserved multi-domain proteins in eukaryotes, serve as pivotal actin organizers, orchestrating the structure and dynamics of the actin cytoskeleton. However, a comprehensive investigation into the formin family and their plausible involvement in abiotic stress remains undocumented in soybean (Glycine max). In the current study, 34 soybean FH (GmFH)family members were discerned, their genomic distribution spanning the twenty chromosomes in a non-uniform pattern. Evolutionary analysis of the FH gene family across plant species delineated five discernible groups (Group I to V) and displayed a closer evolutionary relationship within Glycine soja, Glycine max, and Arabidopsis thaliana. Analysis of the gene structure of GmFH unveiled variable sequence lengths and substantial diversity in conserved motifs. Structural prediction in the promoter regions of GmFH gene suggested a large set of cis-acting elements associated with hormone signaling, plant growth and development, and stress responses. The investigation of the syntenic relationship revealed a greater convergence of GmFH genes with dicots, indicating a close evolutionary affinity. Transcriptome data unveiled distinctive expression patterns of several GmFH genes across diverse plant tissues and developmental stages, underscoring a spatiotemporal regulatory framework governing the transcriptional dynamics of GmFH gene. Gene expression and qRT-PCR analysis identified many GmFH genes with a dynamic pattern in response to abiotic stresses, revealing their potential roles in regulating plant stress adaptation. Additionally, protein interaction analysis highlighted an intricate web of interactions among diverse GmFH proteins. These findings collectively underscore a novel biological function of GmFH proteins in facilitating stress adaptation in soybeans.

OsNAC103, an NAC transcription factor negatively regulates plant height in rice

MAIN CONCLUSION

OsNAC103 negatively regulates rice plant height by influencing the cell cycle and crosstalk of phytohormones. Plant height is an important characteristic of rice farming and is directly related to agricultural yield. Although there has been great progress in research on plant growth regulation, numerous genes remain to be elucidated. NAC transcription factors are widespread in plants and have a vital function in plant growth. Here, we observed that the overexpression of OsNAC103 resulted in a dwarf phenotype, whereas RNA interference (RNAi) plants and osnac103 mutants showed no significant difference. Further investigation revealed that the cell length did not change, indicating that the dwarfing of plants was caused by a decrease in cell number due to cell cycle arrest. The content of the bioactive cytokinin N6-Δ2-isopentenyladenine (iP) decreased as a result of the cytokinin synthesis gene being downregulated and the enhanced degradation of cytokinin oxidase. OsNAC103 overexpression also inhibited cell cycle progression and regulated the activity of the cell cyclin OsCYCP2;1 to arrest the cell cycle. We propose that OsNAC103 may further influence rice development and gibberellin-cytokinin crosstalk by regulating the Oryza sativa homeobox 71 (OSH71). Collectively, these results offer novel perspectives on the role of OsNAC103 in controlling plant architecture.

Recent Advances in Studying the Regulation of Fruit Ripening in Tomato Using Genetic Engineering Approaches

Tomato (Solanum lycopersicum L.) is one of the most commercially essential vegetable crops cultivated worldwide. In addition to the nutritional value, tomato is an excellent model for studying climacteric fruits' ripening processes. Despite this, the available natural pool of genes that allows expanding phenotypic diversity is limited, and the difficulties of crossing using classical selection methods when stacking traits increase proportionally with each additional feature. Modern methods of the genetic engineering of tomatoes have extensive potential applications, such as enhancing the expression of existing gene(s), integrating artificial and heterologous gene(s), pointing changes in target gene sequences while keeping allelic combinations characteristic of successful commercial varieties, and many others. However, it is necessary to understand the fundamental principles of the gene molecular regulation involved in tomato fruit ripening for its successful use in creating new varieties. Although the candidate genes mediate ripening have been identified, a complete picture of their relationship has yet to be formed. This review summarizes the latest (2017-2023) achievements related to studying the ripening processes of tomato fruits. This work attempts to systematize the results of various research articles and display the interaction pattern of genes regulating the process of tomato fruit ripening.

Artificial Light for Improving Tomato Recovery Following Grafting: Transcriptome and Physiological Analyses

Grafting is widely used to enhance the phenotypic traits of tomatoes, alleviate biotic and abiotic stresses, and control soil-borne diseases of the scion in greenhouse production. There are many factors that affect the healing and acclimatization stages of seedlings after grafting. However, the role of light has rarely been studied. In this study, we compared the effects of artificial light and traditional shading (under shaded plastic-covered tunnels) on the recovery of grafted tomato seedlings. The results show that the grafted tomato seedlings recovered using artificial light had a higher healthy index, leaf chlorophyll content, shoot dry weight, and net photosynthetic rate (Pn) and water use efficiency (WUE) compared with grafted seedling recovered using the traditional shading method. Transcriptome analysis showed that the differentially expressed genes (DEGs) of grafted seedlings restored using artificial light were mainly enriched in the pathways corresponding to plant hormone signal transduction. In addition, we measured the endogenous hormone content of grafted tomato seedlings. The results show that the contents of salicylic acid (SA) and kinetin (Kin) were significantly increased, and the contents of indoleacetic acid (IAA) and jasmonic acid (JA) were decreased in artificial-light-restored grafted tomato seedlings compared with those under shading treatments. Therefore, we suggest that artificial light affects the morphogenesis and photosynthetic efficiency of grafted tomato seedlings, and it can improve the performance of tomato seedlings during grafting recovery by regulating endogenous hormone levels.

Transcriptome Analysis Reveals the Molecular Mechanism and Responsive Genes of Waterlogging Stress in Actinidia deliciosa Planch Kiwifruit Plants

Waterlogging stress is one of the major natural issues resulting in stunted growth and loss of agricultural productivity. Cultivated kiwifruits are popular for their rich vitamin C content and unique flavor among consumers, while commonly sensitive to waterlogging stress. The wild kiwifruit plants are usually obliged to survive in harsh environments. Here, we carried out a transcriptome analysis by high-throughput RNA sequencing using the root tissues of Actinidia deliciosa (a wild resource with stress-tolerant phenotype) after waterlogging for 0 d, 3 d, and 7 d. Based on the RNA sequencing data, a high number of differentially expressed genes (DEGs) were identified in roots under waterlogging treatment, which were significantly enriched into four biological processes, including stress response, metabolic processes, molecular transport, and mitotic organization, by gene ontology (GO) simplify enrichment analysis. Among these DEGs, the hypoxia-related genes AdADH1 and AdADH2 were correlated well with the contents of acetaldehyde and ethanol, and three transcription factors Acc26216, Acc08443, and Acc16908 were highly correlated with both AdADH1/2 genes and contents of acetaldehyde and ethanol. In addition, we found that there might be an evident difference among the promoter sequences of ADH genes from A. deliciosa and A. chinensis. Taken together, our results provide additional information on the waterlogging response in wild kiwifruit plants.

Phytohormonal modulation of the drought stress in soybean: outlook, research progress, and cross-talk

Phytohormones play vital roles in stress modulation and enhancing the growth of plants. They interact with one another to produce programmed signaling responses by regulating gene expression. Environmental stress, including drought stress, hampers food and energy security. Drought is abiotic stress that negatively affects the productivity of the crops. Abscisic acid (ABA) acts as a prime controller during an acute transient response that leads to stomatal closure. Under long-term stress conditions, ABA interacts with other hormones, such as jasmonic acid (JA), gibberellins (GAs), salicylic acid (SA), and brassinosteroids (BRs), to promote stomatal closure by regulating genetic expression. Regarding antagonistic approaches, cytokinins (CK) and auxins (IAA) regulate stomatal opening. Exogenous application of phytohormone enhances drought stress tolerance in soybean. Thus, phytohormone-producing microbes have received considerable attention from researchers owing to their ability to enhance drought-stress tolerance and regulate biological processes in plants. The present study was conducted to summarize the role of phytohormones (exogenous and endogenous) and their corresponding microbes in drought stress tolerance in model plant soybean. A total of n=137 relevant studies were collected and reviewed using different research databases.

Flowering induction in cassava using photoperiod extension premature pruning and plant growth regulators

Cassava (Manihot esculenta Crantz) is a vital crop for food and economic security in many regions of the world. Despite the economic and social importance of cassava, challenges persist in developing superior varieties that meet the needs of farmers in terms of agronomic performance, nutritional quality, and resistance to pests and diseases. One of the main obstacles for genetic improvement is the lack of synchronization in flowering and the abortion of young flowers, making planned crosses and progeny production difficult. Therefore, the aim of this study was to evaluate the effect of photoperiod, premature pruning, and growth regulators on cassava flowering under low-altitude conditions in Brazil. Eight cassava clones with contrasting flowering capacity were assessed in Cruz das Almas, Bahia, using two photoperiods (ambient condition and extended photoperiod with red light for 12 hours), premature pruning at the first and second branching levels (with and without pruning), and the application of growth regulators: 0.5 mM 6-benzyladenine (BA) and 4.0 mM silver thiosulfate (STS) (with and without). Plots were assessed weekly for the number of female (NFF) and male (NMF) flowers, height of the first branching (H1B, in cm), number of days to the first branching (ND1B), and the number of branching events up to 240 days after planting (NOB). The extended photoperiod did not promote an increase in the number of flowers but allowed for precocity in cassava flowering, reducing the onset of flowering by up to 35 days, and significantly increasing the number of branches, which is closely related to flowering. The use of pruning and plant growth regulators (PGR) resulted in an increase in NFF from 2.2 (control) to 4.6 and NMF from 8.1 to 21.1 flowers. Therefore, under hot and humid tropical conditions at low altitudes in the Recôncavo of Bahia, manipulating the photoperiod and using premature pruning and plant growth regulators can accelerate cassava flowering, benefiting genetic improvement programs.

Effect of Co-Application of Azospirillum brasilense and Rhizobium pisi on Wheat Performance and Soil Nutrient Status under Deficit and Partial Root Drying Stress

Water management techniques are improving at the farm level, but they are not enough to deal with the limited availability of water and increased crop yields. Soil microbes play a vital role in nitrogen fixation, improving soil fertility and enhancing plant growth hormones under drought conditions. Therefore, this study was conducted to investigate the impact of water management combined with Azospirillum brasilense and Rhizobium pisi on wheat crop productivity and soil properties in dry regions. Three water management techniques were compared, normal irrigation as a control (C), deficit irrigation (DI), and partial root drying irrigation (PRD), together with the interaction of plant-growth-promoting rhizobacteria (PGPR). Experiments were conducted with six treatments in total: T1 = C + No PGPR, T2 = C + PGPR, T3 = DI + No PGPR, T4 = DI + PGPR, T5 = PRD + No PGPR, and T6 = PRD + PGPR. The highest grain yield was achieved in the control irrigation treatment using seeds inoculated with rhizobacteria, followed by control treatment without any inoculation, and the lowest was recorded with deficit irrigation without rhizobacteria inoculated in the seeds. However, PRD irrigation resulted in significantly higher plant growth and grain yield than the DI treatment. PGPR inoculation combined with PRD resulted in a 22% and 20% higher number of grains per spike, a 19% and 21% higher grain yield, and a 25% and 22% higher crop growth rate compared to rhizobacteria inoculation combined with the DI system in 2021-22 and 2022-23, respectively. This increase was due to the higher production of growth hormones and higher leaf area index under water-limited conditions. A greater leaf area index leads to a higher chlorophyll content and higher food production for plant growth.

The role of plant growth promoting rhizobacteria in plant drought stress responses

Climate change has exacerbated the effects of abiotic stresses on plant growth and productivity. Drought is one of the most important abiotic stress factors that interfere with plant growth and development. Plant selection and breeding as well as genetic engineering methods used to improve crop drought tolerance are expensive and time consuming. Plants use a myriad of adaptative mechanisms to cope with the adverse effects of drought stress including the association with beneficial microorganisms such as plant growth promoting rhizobacteria (PGPR). Inoculation of plant roots with different PGPR species has been shown to promote drought tolerance through a variety of interconnected physiological, biochemical, molecular, nutritional, metabolic, and cellular processes, which include enhanced plant growth, root elongation, phytohormone production or inhibition, and production of volatile organic compounds. Therefore, plant colonization by PGPR is an eco-friendly agricultural method to improve plant growth and productivity. Notably, the processes regulated and enhanced by PGPR can promote plant growth as well as enhance drought tolerance. This review addresses the current knowledge on how drought stress affects plant growth and development and describes how PGPR can trigger plant drought stress responses at the physiological, morphological, and molecular levels.

Phosphorus Plays Key Roles in Regulating Plants' Physiological Responses to Abiotic Stresses

Phosphorus (P), an essential macronutrient, plays a pivotal role in the growth and development of plants. However, the limited availability of phosphorus in soil presents significant challenges for crop productivity, especially when plants are subjected to abiotic stresses such as drought, salinity and extreme temperatures. Unraveling the intricate mechanisms through which phosphorus participates in the physiological responses of plants to abiotic stresses is essential to ensure the sustainability of agricultural production systems. This review aims to analyze the influence of phosphorus supply on various aspects of plant growth and plant development under hostile environmental conditions, with a special emphasis on stomatal development and operation. Furthermore, we discuss recently discovered genes associated with P-dependent stress regulation and evaluate the feasibility of implementing P-based agricultural practices to mitigate the adverse effects of abiotic stress. Our objective is to provide molecular and physiological insights into the role of P in regulating plants' tolerance to abiotic stresses, underscoring the significance of efficient P use strategies for agricultural sustainability. The potential benefits and limitations of P-based strategies and future research directions are also discussed.

An analysis of differentially expressed and differentially m6A-modified transcripts in soybean roots treated with lead

Lead is one of the most common toxic heavy metal pollutants in nature, and exposure to lead can cause serious toxicity to many organisms. In this study, we collected root growth data from soybean plants exposed to lead for seven days and confirmed that lead significantly inhibited root growth. We performed a transcriptome-wide m6A methylation analysis to study the response of soybean RNA methylation groups to lead. The m6A modified regions were enriched near the 3'UTR region and stop codon, and m6A methylation was positively correlated with transcript abundance. In the presence of lead, the transcriptome range of m6A RNA methylation peaks increased, and we identified 1144 m6A modification peaks and 1094 differentially expressed genes. The integration of m6A methylation and transcriptomic results enabled us to identify 16 candidate genes whose transcripts were differentially methylated and differentially expressed under lead stress. Annotation results suggest that these genes may promote abiotic stress tolerance by impacting lead uptake, transport, and accumulation through ROS pathways, enzymes, transporters, and hormones. These results provide candidate genes for future studies of lead stress tolerance mechanisms in soybean roots and provide genetic resources for studying plant heavy metal stress in soybean breeding.

Ectopic Expression of a Maize Gene ZmDUF1645 in Rice Increases Grain Length and Yield, but Reduces Drought Stress Tolerance

As the human population grows rapidly, food shortages will become an even greater problem; therefore, increasing crop yield has become a focus of rice breeding programs. The maize gene, ZmDUF1645, encoding a putative member of the DUF1645 protein family with an unknown function, was transformed into rice. Phenotypic analysis showed that enhanced ZmDUF1645 expression significantly altered various traits in transgenic rice plants, including increased grain length, width, weight, and number per panicle, resulting in a significant increase in yield, but a decrease in rice tolerance to drought stress. qRT-PCR results showed that the expression of the related genes regulating meristem activity, such as MPKA, CDKA, a novel crop grain filling gene (GIF1), and GS3, was significantly changed in the ZmDUF1645-overexpression lines. Subcellular colocalization showed that ZmDUF1645 was primarily localized on cell membrane systems. Based on these findings, we speculate that ZmDUF1645, like the OsSGL gene in the same protein family, may regulate grain size and affect yield through the cytokinin signaling pathway. This research provides further knowledge and understanding of the unknown functions of the DUF1645 protein family and may serve as a reference for biological breeding engineering to increase maize crop yield.

Growth, antioxidant system, and phytohormonal status of barley cultivars contrasting in cadmium tolerance

Cadmium leads to disturbance of plant growth, and the manifestation of toxicity can vary greatly in different genotypes within one species. In this work we studied the effect of Cd on growth, antioxidant enzyme activity, and phytohormonal status of four barley cultivars (cvs. Simfoniya, Mestnyj, Ca 220702, Malva). According to the earlier study on seedlings, these cultivars were contrast in tolerance to Cd: Simfoniya and Mestnyj are Cd-tolerant and Ca 220702 and Malva are Cd-sensitive. The results presented showed that barley plants accumulated more Cd in straw than in grain. Tolerant cultivars accumulated significantly less Cd in grain than sensitive ones. The leaf area appeared to be a growth parameter susceptible to Cd treatment. The significant differences in leaf area values depended on Cd contamination and were not associated with cultivars' tolerance. Tolerance of cultivars was contingent on the activity of the antioxidant defense system. Indeed, activity of enzymes decreased in sensitive cultivars Ca 220702 and Malva under Cd stress. In contrast, in tolerant cultivars, increased activity of guaiacol peroxidase was revealed. The concentrations of abscisic acid and salicylic acid mostly increased as a result of Cd treatment, while the concentrations of auxins and trans-zeatin either decreased or did not change. The results obtained indicate that antioxidant enzymes and phytohormones play an important role in the response of barley plants to elevated concentrations of cadmium; however, these parameters are not able to explain the differentiation of barley cultivars in terms of tolerance to cadmium at the seedling stage. Therefore, barley intraspecific polymorphism for cadmium resistance is determined by the interplay of antioxidant enzymes, phytohormones, and other factors that require further elucidation.

Multi-Knock-a multi-targeted genome-scale CRISPR toolbox to overcome functional redundancy in plants

Plant genomes are characterized by large and complex gene families that often result in similar and partially overlapping functions. This genetic redundancy severely hampers current efforts to uncover novel phenotypes, delaying basic genetic research and breeding programmes. Here we describe the development and validation of Multi-Knock, a genome-scale clustered regularly interspaced short palindromic repeat toolbox that overcomes functional redundancy in Arabidopsis by simultaneously targeting multiple gene-family members, thus identifying genetically hidden components. We computationally designed 59,129 optimal single-guide RNAs that each target two to ten genes within a family at once. Furthermore, partitioning the library into ten sublibraries directed towards a different functional group allows flexible and targeted genetic screens. From the 5,635 single-guide RNAs targeting the plant transportome, we generated over 3,500 independent Arabidopsis lines that allowed us to identify and characterize the first known cytokinin tonoplast-localized transporters in plants. With the ability to overcome functional redundancy in plants at the genome-scale level, the developed strategy can be readily deployed by scientists and breeders for basic research and to expedite breeding efforts.

Influences of Natural Antioxidants, Reactive Oxygen Species and Compatible Solutes of Panicum Miliaceum L. Towards Drought Stress

In proso millet, in certain circumstances, drought stress greatly influences growth and metabolisms. Thus, the present study was aimed to examine morphological, biochemical and ROS mechanisms between plant and drought stress in Panicum miliaceum L. To create the drought condition, water irrigation was done at different time intervals including 4, 7, 10, 13 days and control. All the experiments were carried out at different maturity stages such as 30, 50, and 70 days (after sowing). The results demonstrated that the root length, proline, glycine betaine, amino acid and superoxide dismutase, catalase and peroxidase activities were boosted in all treatments as compared with control. As the proso millet matured, the length of shoots and the amount of chlorophyll pigment in the leaves reduced in all treatments as compared to control. Induced reduction of shoot growth, chlorophyll estimation and increases of root growth, osmolyte accumulations, antioxidant enzymes, were found to be drought-tolerant adaptative mechanisms in this study.

B-type response regulator hst1 controls salinity tolerance in rice by regulating transcription factors and antioxidant mechanisms

Salinity is a serious environmental problem that limits plant yield in almost half of the agricultural fields. The hitomebore salt tolerant 1(hst1) is a mutant B-type response regulator gene that was reported to improve salinity tolerance in the 'YNU31-2-4' (YNU) genotype. The sister line (SL) is salt-sensitive, and the nearest genomic relative of the YNU plant has the OsRR22 gene, which is the non-mutant form of the hst1 gene. Biochemical and comprehensive transcriptome analysis of SL and YNU plants was performed to clarify the salinity tolerance mechanism(s) mediated by the hst1 gene. The hst1 gene reduced Na⁺ ions, lipid peroxidation, and H₂O₂ content, and improve proline and antioxidant enzymes activities under salt stress. Various transporter and gene-specific transcriptional regulator genes up-regulated in presence of the hst1 gene under saline conditions, identifying that post-stress transcription factors (OsbHLH056, OsH43, OsGRAS29, and OsMADS1) contributed to improved salinity tolerance in YNU plants. Specifically, OsSalT, miR156, and OsLPT1.16 genes were up-regulated, while upstream (OsHKs and OsHPs) and downstream regulators of the OsRR22 gene were down-regulated in YNU plants under saline conditions. Notably, the transcription factors reprogramming, upstream and downstream genes, indicate that these pathways are transcriptionally regulated by the hst1 gene. The findings of the regulatory role of the hst1 gene on plant transcriptome provide a greater understanding of hst1-mediated salt tolerance in rice plants. This knowledge will contribute to understanding the salinity tolerance mechanisms in rice and the evolution of salt-tolerant crops with the ability to withstand higher salinity to ensure food security during climate change.

Emergence of an Auxin Sensing Domain in Plant-Associated Bacteria

Bacteria have evolved a sophisticated array of signal transduction systems that allow them to adapt their physiology and metabolism to changing environmental conditions. Typically, these systems recognize signals through dedicated ligand binding domains (LBDs) to ultimately trigger a diversity of physiological responses. Nonetheless, an increasing number of reports reveal that signal transduction receptors also bind antagonists to inhibit responses mediated by agonists. The mechanisms by which antagonists block the downstream signaling cascade remain largely unknown. To advance our knowledge in this field, we used the LysR-type transcriptional regulator AdmX as a model. AdmX activates the expression of an antibiotic biosynthetic cluster in the rhizobacterium Serratia plymuthica. AdmX specifically recognizes the auxin phytohormone indole-3-acetic acid (IAA) and its biosynthetic intermediate indole-3-pyruvic acid (IPA) as signals. However, only IAA, but not IPA, was shown to regulate antibiotic production in S. plymuthica. Here, we report the high-resolution structures of the LBD of AdmX in complex with IAA and IPA. We found that IAA and IPA compete for binding to AdmX. Although IAA and IPA binding does not alter the oligomeric state of AdmX, IPA binding causes a higher degree of compactness in the protein structure. Molecular dynamics simulations revealed significant differences in the binding modes of IAA and IPA by AdmX, and the inspection of the three-dimensional structures evidenced differential agonist- and antagonist-mediated structural changes. Key residues for auxin binding were identified and an auxin recognition motif defined. Phylogenetic clustering supports the recent evolutionary emergence of this motif specifically in plant-associated enterobacteria. IMPORTANCE Although antagonists were found to bind different bacterial signal transduction receptors, we are still at the early stages of understanding the molecular details by which these molecules exert their inhibitory effects. Here, we provide insight into the structural changes resulting from the binding of an agonist and an antagonist to a sensor protein. Our data indicate that agonist and antagonist recognition is characterized by small conformational differences in the LBDs that can be efficiently transmitted to the output domain to modulate the final response. LBDs are subject to strong selective pressures and are rapidly evolving domains. An increasing number of reports support the idea that environmental factors drive the evolution of sensor domains. Given the recent evolutionary history of AdmX homologs, as well as their narrow phyletic distribution within plant-associated bacteria, our results are in accordance with a plant-mediated evolutionary process that resulted in the emergence of receptor proteins that specifically sense auxin phytohormones.

Jasmonic acid enhances osmotic stress responses by MYC2-mediated inhibition of protein phosphatase 2C1 and response regulators 26 transcription factor in tomato

The jasmonic acid (JA) signaling pathway is involved in the plant response to drought stress. JA and other hormones synergistically regulate the drought response in plants. However, the molecular mechanism underlying this synergism remains poorly defined. In the present study, transcriptome analyses of guard cells and quantitative PCR experiments revealed that MYC2 negatively regulated the negative regulator of ABA signaling, SlPP2C1, and the type-B response regulator in the cytokinin pathway, SlRR26, and this negative regulation was direct. SlRR26 overexpression reduced drought tolerance in transgenic tomatoes, whereas slrr26^cr lines were more tolerant to drought. SlRR26 negatively modulated reactive oxygen species levels in stomata and stomatal closure through RobhB. Moreover, SlRR26 overexpression counteracted JA-mediated stomatal closure, suggesting that SlRR26 played a negative role in the JA-mediated drought response. These findings suggest that MYC2 plays a key role in JA-regulated stomatal closure under drought stress by inhibiting SlPP2C1 and SlRR26.

Molecular Regulation and Evolution of Cytokinin Signaling in Plant Abiotic Stresses

The sustainable production of crops faces increasing challenges from global climate change and human activities, which leads to increasing instances of many abiotic stressors to plants. Among the abiotic stressors, drought, salinity and excessive levels of toxic metals cause reductions in global agricultural productivity and serious health risks for humans. Cytokinins (CKs) are key phytohormones functioning in both normal development and stress responses in plants. Here, we summarize the molecular mechanisms on the biosynthesis, metabolism, transport and signaling transduction pathways of CKs. CKs act as negative regulators of both root system architecture plasticity and root sodium exclusion in response to salt stress. The functions of CKs in mineral-toxicity tolerance and their detoxification in plants are reviewed. Comparative genomic analyses were performed to trace the origin, evolution and diversification of the critical regulatory networks linking CK signaling and abiotic stress. We found that the production of CKs and their derivatives, pathways of signal transduction and drought-response root growth regulation are evolutionarily conserved in land plants. In addition, the mechanisms of CK-mediated sodium exclusion under salt stress are suggested for further investigations. In summary, we propose that the manipulation of CK levels and their signaling pathways is important for plant abiotic stress and is, therefore, a potential strategy for meeting the increasing demand for global food production under changing climatic conditions.

Genome-wide identification and expression analysis of two-component system genes in sweet potato (Ipomoea batatas L.)

Two-component system (TCS), which comprises histidine kinases (HKs), histidine phosphotransfer proteins (HPs), and response regulators (RRs), plays essential roles in regulating plant growth, development, and response to various environmental stimuli. TCS genes have been comprehensively identified in various plants, while studies on the genome-wide identification and analysis of TCS in sweet potato were still not reported. Therefore, in this study, a total of 90 TCS members consisting of 20 HK(L)s, 11 HPs, and 59 RRs were identified in the genome of Ipomoea batatas. Furthermore, their gene structures, conserved domains, and phylogenetic relationships were analyzed in detail. Additionally, the gene expression profiles in various organs were analyzed, and response patterns to adverse environmental stresses were investigated. The results showed that these 90 TCS genes were mapped on 15 chromosomes with a notably uneven distribution, and the expansion of TCS genes in sweet potato was attributed to both segmental and tandem duplications. The majority of the TCS genes showed distinct organ-specific expression profiles, especially in three types of roots (stem roots, fibrous roots, tuberous roots). Moreover, most of the TCS genes were either induced or suppressed upon treatment with abiotic stresses (drought, salinity, cold, heat) and exogenous phytohormone abscisic acid (ABA). In addition, the yeast-two hybrid system was used to reveal the HK-HP-RR protein-protein interactions. IbHP1, IbHP2, IbHP4, and IbHP5 could interact with three HKs (IbHK1a, IbHK1b, and IbHK5), and also interact with majority of the type-B RRs (IbRR20-IbRR28), while no interaction affinity was detected for IbHP3. Our systematic analyses could provide insights into the characterization of the TCS genes, and further the development of functional studies in sweet potato.

Effects of the application of forchlorfenuron (CPPU) on the composition of verdejo grapes

The application of cytokinins such as forchlorfenuron (CPPU) has been widely used in table grape varieties to increase yield and berry size. However, the potential interest of these phytoregulators in wine grapes have been scarcely analyzed. The objective of this study has been to evaluate the influence of CPPU treatment on the agronomic performance and composition of Verdejo grapes. The trial was conducted in 2021, in the Protected Designation of Origin “Rueda” (Spain). CPPU was applied using a concentration of 15 mg/L, by spraying the bunches when the berries were 5-6 mm in diameter. The photosynthesis rates and the stem water potential, measured after the application, tended to decrease in the treated plants without modify the values ​​of vine yield and vigour. The treatment significantly affected the content of soluble solids and total polyphenols of the grape must, detecting increases of 15.4% and 7%, respectively, compared to the controls. Preliminary results suggest that the application of CPPU on the bunches could improve the quality of the Verdejo grapes. The treatment would be interesting to apply in cultivation conditions where the harvest has difficulties to reach an adequate level of maturity, such as excessive vigour or too cold climate.

CcRR5 interacts with CcRR14 and CcSnRK2s to regulate the root development in citrus

Response regulator (RR) is an important component of the cytokinin (CK) signal transduction system associated with root development and stress resistance in model plants. However, the function of RR gene and the molecular mechanism on regulating the root development in woody plants such as citrus remain unclear. Here, we demonstrate that CcRR5, a member of the type A RR, regulates the morphogenesis of root through interacting with CcRR14 and CcSnRK2s in citrus. CcRR5 is mainly expressed in root tips and young leaves. The activity of CcRR5 promoter triggered by CcRR14 was proved with transient expression assay. Seven SnRK2 family members with highly conserved domains were identified in citrus. Among them, CcSnRK2.3, CcSnRK2.6, CcSnRK2.7, and CcSnRK2.8 can interact with CcRR5 and CcRR14. Phenotypic analysis of CcRR5 overexpressed transgenic citrus plants indicated that the transcription level of CcRR5 was associated with root length and lateral root numbers. This was also correlated to the expression of root-related genes and thus confirmed that CcRR5 is involved in the root development. Taken together, the results of this study indicate that CcRR5 is a positive regulator of root growth and CcRR14 directly regulates the expression of CcRR5. Both CcRR5 and CcRR14 can interact with CcSnRK2s.

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.

Identification of LsPIN1 gene and its potential functions in rhizome turning of Leymus secalinus

Background

Continuous tilling and the lateral growth of rhizomes confer rhizomatous grasses with the unique ability to laterally expand, migrate and resist disturbances. They play key roles especially in degraded grasslands, deserts, sand dunes, and other fragile ecological system. The rhizomatous plant Leymus secalinus has both rhizome buds and tiller buds that grow horizontally and upward at the ends of rhizome differentiation and elongation, respectively. The mechanisms of rhizome formation and differentiation in L. secalinus have not yet been clarified.

Results

In this study, we found that the content of gibberellin A3 (GA3) and indole-3-acetic acid (IAA) were significantly higher in upward rhizome tips than in horizontal rhizome tips; by contrast, the content of methyl jasmonate and brassinolide were significantly higher in horizontal rhizome tips than in upward rhizome tips. GA3 and IAA could stimulate the formation and turning of rhizomes. An auxin efflux carrier gene, LsPIN1, was identified from L. secalinus based on previous transcriptome data. The conserved domains of LsPIN1 and the relationship of LsPIN1 with PIN1 genes from other plants were analyzed. Subcellular localization analysis revealed that LsPIN1 was localized to the plasma membrane. The length of the primary roots (PRs) and the number of lateral roots (LRs) were higher in Arabidopsis thaliana plants overexpressing LsPIN1 than in wild-type (Col-0) plants. Auxin transport was altered and the gravitropic response and phototropic response were stronger in 35S:LsPIN1 transgenic plants compared with Col-0 plants. It also promoted auxin accumulation in root tips.

Conclusion

Our findings indicated that LsPIN1 plays key roles in auxin transport and root development. Generally, our results provide new insights into the regulatory mechanisms underlying rhizome development in L. secalinus.

The histidine phosphotransfer AHP4 plays a negative role in Arabidopsis plant response to drought

Cytokinin plays an important role in plant stress responses via a multistep signaling pathway, involving the histidine phosphotransfer proteins (HPs). In Arabidopsis thaliana, the AHP2, AHP3 and AHP5 proteins are known to affect drought responses; however, the role of AHP4 in drought adaptation remains undetermined. In the present study, using a loss-of-function approach we showed that AHP4 possesses an important role in the response of Arabidopsis to drought. This is evidenced by the higher survival rates of ahp4 than wild-type (WT) plants under drought conditions, which is accompanied by the downregulated AHP4 expression in WT during periods of dehydration. Comparative transcriptome analysis of ahp4 and WT plants revealed AHP4-mediated expression of several dehydration- and/or abscisic acid-responsive genes involved in modulation of various physiological and biochemical processes important for plant drought acclimation. In comparison with WT, ahp4 plants showed increased wax crystal accumulation in stems, thicker cuticles in leaves, greater sensitivity to exogenous abscisic acid at germination, narrow stomatal apertures, heightened leaf temperatures during dehydration, and longer root length under osmotic stress. In addition, ahp4 plants showed greater photosynthetic efficiency, lower levels of reactive oxygen species, reduced electrolyte leakage and lipid peroxidation, and increased anthocyanin contents under drought, when compared with WT. These differences displayed in ahp4 plants are likely due to upregulation of genes that encode enzymes involved in reactive oxygen species scavenging and non-enzymatic antioxidant metabolism. Overall, our findings suggest that AHP4 plays a crucial role in plant drought adaptation.

Cytokinin or ethylene regulation of heat-induced leaf senescence involving transcriptional modulation of WRKY in perennial ryegrass

Heat stress is a major abiotic stress for temperate plant species with characteristic symptoms of premature leaf senescence. The objectives of this study were to evaluate the physiological effects of cytokinins (CK) and an ethylene inhibitor, aminoethoxyvinylglycine (AVG) on heat-induced leaf senescence in the temperate perennial grass species, perennial ryegrass (Lolium perenne), and to investigate whether WRKY transcription factors (TFs) could be associated with CK- or ethylene-mediated regulation of heat-induced leaf senescence by exogenously applying CK or AVG to perennial ryegrass. Perennial ryegrass plants foliar-sprayed with 6-benzylaminopurine (6-BA), and AVG exhibited prolonged stay-green phenotypes and a lesser degree of leaf senescence under heat stress (35/30°C), as shown by a decline in electrolyte leakage, malondialdehyde content, hydrogen peroxide, and superoxide content, and increased chlorophyll (Chl) content along with reduced activities of Chl-degrading enzymes (pheophytinase and chlorophyllase) and increased activity of Chl-synthesizing enzyme (porphobilinogen deaminase) due to 6-BA or AVG application. The suppression of heat-induced leaf senescence by 6-BA or AVG treatment corresponded with the upregulation of LpWRKY69 and LpWRKY70. The LpWRKY69 and LpWRKY70 promoters were predicted to share conserved cis-elements potentially recognized by TFs in the CK or ethylene pathways. These results indicate that LpWRKY69 and LpWRKY70 may negatively regulate heat-induced leaf senescence through CK or ethylene pathways, conferring heat tolerance in perennial ryegrass.

The bioactive potential of phytohormones: A review

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Phytohormones act as bioactive compound for plant, humans and microbes.

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Cytokinin, GA and auxin reduce reactive oxygen to prevent cancer & tumour disease.

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Phytohormones used in pharmaceuticals products and cosmetics for human.

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Microbes can be a potential source for plant hormones production.

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Phytohormones play a key role in signalling for plant-animal–microbe interactions.

Plant hormones play an important role in growth, defence and plants productivity and there are several studies on their effects on plants. However, their role in humans and animals is limitedly studied. Recent studies suggest that plant hormone also works in mammalian systems, and have the potential to reduce human diseases such as cancer, diabetes, and also improve cell growth. Plant hormones such as indole-3-acetic acid (IAA) works as an antitumor, anti-cancer agent, gibberellins help in apoptosis, abscisic acid (ABA) as antidepressant compounds and regulation of glucose homeostasis whereas cytokinin works as an anti-ageing compound. The main aim of this review is to explore and correlate the relation of plant hormones and their important roles in animals, microbes and plants, and their interrelationships, emphasizing mainly human health. The most important and well-known plant hormones e.g., IAA, gibberellins, ABA, cytokinin and ethylene have been selected in this review to explore their effects on humans and animals.

How does UV-B stress affect secondary metabolites of Scutellaria baicalensis in vitro shoots grown at different 6-benzyl aminopurine concentrations?

Ultraviolet-B (UV-B) radiation is one of the abiotic stresses that can significantly affect the secondary metabolite accumulation in in vitro tissue cultures of medicinal plants. The present study investigated the effects of UV-B radiation on the secondary metabolites and antioxidant activities of Scutellaria baicalensis in vitro shoots grown at different concentrations of 6-benzyl aminopurine (6-BA), which is the cytokinin most widely used in plant tissue culture. The UV-B radiation caused significant increases in lipid peroxidation, total phenolic, and flavonoid contents, and antioxidant activities in the in vitro shoots grown at lower 6-BA concentrations (0 and 1 mg L^-1 ), while it did not cause any significant changes in those grown at higher 6-BA concentrations (2 and 3 mg L^-1 ). However, the UV-B radiation significantly altered the contents of main individual flavonoids at both lower and higher 6-BA concentrations. Upon UV-B radiation, aglycones (including baicalein, wogonin, and scutellarein) increased, while glucuronides such as baicalin and wogonoside decreased; this was more evident at higher 6-BA concentrations. This study demonstrated that the effects of UV-B radiation on the secondary metabolites of S. baicalensis in vitro shoots highly depended on the 6-BA concentration in the culture medium.

Genome-wide identification and expression analysis of the TaRRA gene family in wheat (Triticum aestivum L.)

Cytokinin is an important endogenous hormone in plants performing a wide spectrum of biological roles. The type-A response regulators (RRAs) are primary cytokinin response genes, which are important components of the cytokinin signaling pathway and are involved in the regulation of plant growth and development. By analysis of the whole genome sequence of wheat, we identified 20 genes encoding RRAs which were clustered into eight homologous groups. The gene structure, conserved motifs, chromosomal location, and cis-acting regulatory elements of the TaRRAs were analyzed. Quantitative real-time polymerase chain reaction (qRT-PCR) results showed that the expression levels of most of the TaRRAs increased rapidly on exogenous cytokinin application. Moreover, the TaRRA family members displayed different expression profiles under the stress treatments of drought, salt, cold, and heat. This study provides valuable insights into the RRA gene family in wheat and promotes the potential application of these genes in wheat genetic improvement.

Cytokinin Deficiency Alters Leaf Proteome and Metabolome during Effector-Triggered Immunity in Arabidopsis thaliana Plants

The involvement of cytokinins (CK) in biotic stresses has been recognized, while knowledge regarding the effects of CK deficiency on plant response against pathogens is less abundant. Thus, the purpose of this study was to reveal the effects of CK deficiency on proteomics and metabolomic responses of flg22-triggered immunity. We conducted a series of histochemical assays to investigate the activity of the downstream pathways caused by flg22, such as accumulation of ROS, induction of defence genes, and callose deposition, that occurred in Arabidopsis thaliana transgenic lines overexpressing the Hordeum vulgare CKX2 gene (HvCKX2), which are therefore CK-deficient. We also used GC and LC-MS-based technology to quantify variations in stress hormone levels and metabolomic and proteomic responses in flg22-treated HvCKX2 and wild-type Arabidopsis plants. We found that CK deficiency alters the flg22-triggered plant defence response, especially through induction of callose deposition, upregulation of defence response-related proteins, increased amino acid biosynthesis, and regulation of plant photosynthesis. We also indicated that JA might be an important contributor to immune response in plants deficient in CKs. The present study offers new evidence on the fundamental role of endogenous CK in the response to pathogens, as well as the possibility of altering plant biotic tolerance by manipulating CK pools.

Cytokinin and abiotic stress tolerance -What has been accomplished and the way forward?

More than a half-century has passed since it was discovered that phytohormone cytokinin (CK) is essential to drive cytokinesis and proliferation in plant tissue culture. Thereafter, cytokinin has emerged as the primary regulator of the plant cell cycle and numerous developmental processes. Lately, a growing body of evidence suggests that cytokinin has a role in mitigating both abiotic and biotic stress. Cytokinin is essential to defend plants against excessive light exposure and a unique kind of abiotic stress generated by an altered photoperiod. Secondly, cytokinin also exhibits multi-stress resilience under changing environments. Furthermore, cytokinin homeostasis is also affected by several forms of stress. Therefore, the diverse roles of cytokinin in reaction to stress, as well as its interactions with other hormones, are discussed in detail. When it comes to agriculture, understanding the functioning processes of cytokinins under changing environmental conditions can assist in utilizing the phytohormone, to increase productivity. Through this review, we briefly describe the biological role of cytokinin in enhancing the performance of plants growth under abiotic challenges as well as the probable mechanisms underpinning cytokinin-induced stress tolerance. In addition, the article lays forth a strategy for using biotechnological tools to modify genes in the cytokinin pathway to engineer abiotic stress tolerance in plants. The information presented here will assist in better understanding the function of cytokinin in plants and their effective investigation in the cropping system.

ZmIAA5 regulates maize root growth and development by interacting with ZmARF5 under the specific binding of ZmTCP15/16/17

Background

The auxin indole-3-acetic acid (IAA) is a type of endogenous plant hormone with a low concentration in plants, but it plays an important role in their growth and development. The AUX/IAA gene family was found to be an early sensitive auxin gene with a complicated way of regulating growth and development in plants. The regulation of root growth and development by AUX/IAA family genes has been reported in Arabidopsis, rice and maize.

Results

In this study, subcellular localization indicated that ZmIAA1-ZmIAA6 primarily played a role in the nucleus. A thermogram analysis showed that AUX/IAA genes were highly expressed in the roots, which was also confirmed by the maize tissue expression patterns. In maize overexpressing ZmIAA5, the length of the main root, the number of lateral roots, and the stalk height at the seedling stage were significantly increased compared with those of the wild type, while the EMS mutant zmiaa5 was significantly reduced. The total number of roots and the dry weight of maize overexpressing ZmIAA5 at the mature stage were also significantly increased compared with those of the wild type, while those of the mutant zmiaa5 was significantly reduced. Yeast one-hybrid experiments showed that ZmTCP15/16/17 could specifically bind to the ZmIAA5 promoter region. Bimolecular fluorescence complementation and yeast two-hybridization indicated an interaction between ZmIAA5 and ZmARF5.

Conclusions

Taken together, the results of this study indicate that ZmIAA5 regulates maize root growth and development by interacting with ZmARF5 under the specific binding of ZmTCP15/16/17.

Identification of BcARR Genes and CTK Effects on Stalk Development of Flowering Chinese Cabbage

Flowering Chinese cabbage (Brassica campestris L. ssp. Chinensis var. utilis Tsen et Lee) is an important and extensively cultivated vegetable in south China, whose major food product is the stalk. In the process of stalk formation, its initiation and development are regulated by a series of hormonal signals, such as cytokinin and gibberellin. In this study, we analyzed the effects of zeatin (ZT) and gibberellin A3 (GA3), and their interaction, on the bolting of flowering Chinese cabbage. The results indicated that the three-true-leaf spraying of ZT and GA synthesis inhibitor (PAC) inhibited plant height but increased stem diameter. Cytokinin (CTK) synthesis inhibitor (YZJ) and GA3 treatment increased plant height and decreased stem diameter. In addition, ZT and GA3 co-treated plants displayed antagonistic effect. Further, 19 type-B authentic response regulators (ARR-Bs), the positive regulators of cytokinin signal transduction were identified from flowering Chinese cabbage. Comprehensive analysis of phylogeny showed BcARR-Bs clustered into three subfamilies with 10 conserved motifs. Analysis of their expression patterns in different tissues and at various growth stage, and their response to hormone treatment suggest that ARR1-b localized in the nucleus displayed unique highest expression patterns in stem tips, are responsive both to ZT and GA, suggesting a significant role in mediating the crosstalk of ZT and GA in the bolting of flowering Chinese cabbage.

Strigolactones and Cytokinin Interaction in Buds in the Control of Rice Tillering

Shoot branching is among the most crucial morphological traits in rice (Oryza sativa L.) and is physiologically modulated by auxins, cytokinins (CKs), and strigolactones (SLs) cumulatively in rice. A number of studies focused on the interplay of these three hormones in regulating rice tiller extension. The present study primarily aimed at determining the impact of different treatments, which were used to regulate rice tiller and axillary bud development on node 2 at the tillering stage and full heading stage, respectively. Transcription levels of several genes were quantified through qRT-PCR analysis, and an endogenous auxin and four types of CKs were determined through LC-MS/MS. Both nutrient deficiency and exogenous SL supply were found to inhibit rice tiller outgrowth by reducing the CK content in the tiller buds. Furthermore, supplying the inhibitor of both exogenous SLs and endogenous SL synthesis could also affect the expression level of OsCKX genes but not the OsIPT genes. Comparison of OsCKX gene expression pattern under exogenous SL and CK supply suggested that the induction of OsCKX expression was most likely via a CK-induced independent pathway. These results combined with the expression of CK type-A RR genes in bud support a role for SLs in regulating bud outgrowth through the regulation of local CK levels. SL functioned antagonistically with CK in regulating the outgrowth of buds on node 2, by promoting the OsCKX gene expression in buds.

Heavy metal induced regulation of plant biology: Recent insights

The presence of different forms of heavy metals in the earth crust is very primitive and probably associated with the origin of plant life. However, since the beginning of human civilisation, heavy metal use and its contamination to all living systems on earth have significantly increased due to human anthropogenic activities. Heavy metals are nonbiodegradable, which directly or indirectly impact photosynthesis, antioxidant system, mineral nutrition status, phytohormones and amino acid-derived molecules. Due to the toxic behaviour of some heavy metals, the endogenous status of chemical messengers like phytohormones may get significantly influenced, leading to harmful impacts on plant growth, development and overall yield of the plants. It has been noticed that exogenous application of phytohormones, that is, abscisic acid, salicylic acid, auxins, brassinosteroids, cytokinins, ethylene and gibberellins can positively regulate the heavy metal toxicity in plants through the regulation of the ascorbate-glutathione cycle, nitrogen metabolism, proline metabolisms, transpiration rate, and cell division. Furthermore, it may also restrict the entry of heavy metals into the plant cells, which aids in the recovery of plant growth and productivity. Besides these, some defence molecules also assist the plant in dealing with heavy metal toxicity. Therefore, the present review aims to bridge the knowledge gap in this context and present outstanding discoveries related to plant life supportive processes during stressful conditions including phytohormones and heavy metal crosstalk along with suggestions for future research in this field.

Involvement of cytokinins in STOP1-mediated resistance to proton toxicity

STOP1 (sensitive to proton rhizotoxicity1) is a master transcription factor that governs the expression of a set of regulatory and structural genes involved in resistance to aluminum and low pH (i.e., proton) stresses in Arabidopsis. However, the mechanisms and regulatory networks underlying STOP1-mediated resistance to proton stresses are largely unclear. Here, we report that low-pH stresses severely inhibited root growth of the stop1 plants by suppressing root meristem activities. Interestingly, the stop1 plants were less sensitive to exogenous cytokinins at normal and low pHs than the wild type. Significantly, low concentrations of cytokinins promoted root growth of the stop1 mutant under low-pH stresses. Moreover, lateral and adventitious root formation was stimulated in stop1 and by low-pH stresses but suppressed by cytokinins. Further studies of the expression patterns of a cytokinin signaling reporter suggest that both the loss-of-function mutation of STOP1 and low-pH stresses suppressed cytokinin signaling outputs in the root. Furthermore, the expression of critical genes involved in cytokinin biosynthesis, biodegradation, and signaling is altered in the stop1 mutant in response to low-pH stresses. In conclusion, our results reveal a complex network of resistance to low-pH stresses, which involves coordinated actions of STOP1, cytokinins, and an additional low-pH-resistant mechanism for controlling root meristem activities and root growth upon proton stresses.

Stereoselective metabolomic and lipidomic responses of lettuce (Lactuca sativa L.) exposing to chiral triazole fungicide tebuconazole

In this study, non-targeted and targeted metabolomics/lipidomics studies based on UPLC-QTOF-MS and UPLC-MS/MS were carried out to clarify the effects of tebuconazole and its different enantiomers on lettuce metabolites and lipids. Slight enantioselective degradation of tebuconazole was observed and six degradation metabolites were tentatively identified. The endogenous metabolites involved in carbohydrate metabolism, amino acid metabolism, nucleic acid metabolism, phenylpropanoid and flavonoid metabolism, vitamins, and lipid metabolism were significantly affected with enantioselectivity by tebuconazole exposure. Nucleotide metabolism and nicotinic acid metabolic network were significantly activated by the stimulation of tebuconazole. Rac- and (-)-R-tebuconazole caused the down-regulation of soluble sugars and subsequent amino acids and organic acids. Overall, lettuce exposed to tebuconazole was shown to have a significant impact on plant metabolism and lipid metabolism, with notable stereoselectivity. The results showed stereoselective toxicity of tebuconazole and provided a better understanding of its metabolomic and lipidomic effects on lettuce.

Cytokinins is involved in regulation of tomato pericarp thickness and fruit size

Although cytokinins (CKs) regulate fruit development, no direct genetic evidence supports the role of endogenous CKs in pericarp growth or development or fruit size. Here, we report that the reduction in endogenous active CKs level via overexpression of a CKs-inactivating enzyme gene AtCKX2 specifically in fruit tissues resulted in reduced pericarp thickness and smaller fruit size, compared to wild-type control fruits. The pericarp thickness and single fruit weight in transgenic plants were significantly reduced. Analysis of paraffin sections showed that the reduced pericarp thickness was due largely to a decreased number of cells, and thus decreased cell division. Transcriptome profiling showed that the expression of cell division- and expansion-related genes was reduced in AtCKX2-overexpressing fruits. In addition, the expression of auxin-signaling and gibberellin-biosynthetic genes was repressed, whereas that of gibberellin-inactivating genes was enhanced, in AtCKX2-overexpressing fruits. These results demonstrate that endogenous CKs regulate pericarp cell division and, subsequently, fruit size. They also suggest that CKs interact with auxin and gibberellins in regulating tomato pericarp thickness and fruit size.

Phytohormones Trigger Drought Tolerance in Crop Plants: Outlook and Future Perspectives

In the past and present, human activities have been involved in triggering global warming, causing drought stresses that affect animals and plants. Plants are more defenseless against drought stress; and therefore, plant development and productive output are decreased. To decrease the effect of drought stress on plants, it is crucial to establish a plant feedback mechanism of resistance to drought. The drought reflex mechanisms include the physical stature physiology and biochemical, cellular, and molecular-based processes. Briefly, improving the root system, leaf structure, osmotic-balance, comparative water contents and stomatal adjustment are considered as most prominent features against drought resistance in crop plants. In addition, the signal transduction pathway and reactive clearance of oxygen are crucial mechanisms for coping with drought stress via calcium and phytohormones such as abscisic acid, salicylic acid, jasmonic acid, auxin, gibberellin, ethylene, brassinosteroids and peptide molecules. Furthermore, microorganisms, such as fungal and bacterial organisms, play a vital role in increasing resistance against drought stress in plants. The number of characteristic loci, transgenic methods and the application of exogenous substances [nitric oxide, (C28H48O6) 24-epibrassinolide, proline, and glycine betaine] are also equally important for enhancing the drought resistance of plants. In a nutshell, the current review will mainly focus on the role of phytohormones and related mechanisms involved in drought tolerance in various crop plants.

A manipulation of carotenoid metabolism influence biomass partitioning and fitness in tomato

Improving yield, nutritional value and tolerance to abiotic stress are major targets of current breeding and biotechnological approaches that aim at increasing crop production and ensuring food security. Metabolic engineering of carotenoids, the precursor of vitamin-A and plant hormones that regulate plant growth and response to adverse growth conditions, has been mainly focusing on provitamin A biofortification or the production of high-value carotenoids. Here, we show that the introduction of a single gene of the carotenoid biosynthetic pathway in different tomato cultivars induced profound metabolic alterations in carotenoid, apocarotenoid and phytohormones pathways. Alterations in isoprenoid- (abscisic acid, gibberellins, cytokinins) and non-isoprenoid (auxin and jasmonic acid) derived hormones together with enhanced xanthophyll content influenced biomass partitioning and abiotic stress tolerance (high light, salt, and drought), and it caused an up to 77% fruit yield increase and enhanced fruit's provitamin A content. In addition, metabolic and hormonal changes led to accumulation of key primary metabolites (e.g. osmoprotectants and antiaging agents) contributing with enhanced abiotic stress tolerance and fruit shelf life. Our findings pave the way for developing a new generation of crops that combine high productivity and increased nutritional value with the capability to cope with climate change-related environmental challenges.

The Active Phytohormone in Microalgae: The Characteristics, Efficient Detection, and Their Adversity Resistance Applications

Phytohormones are a class of small organic molecules that are widely used in higher plants and microalgae as chemical messengers. Phytohormones play a regulatory role in the physiological metabolism of cells, including promoting cell division, increasing stress tolerance, and improving photosynthetic efficiency, and thereby increasing biomass, oil, chlorophyll, and protein content. However, traditional abiotic stress methods for inducing the accumulation of energy storage substances in microalgae, such as high light intensity, high salinity, and heavy metals, will affect the growth of microalgae and will ultimately limit the efficient accumulation of energy storage substances. Therefore, the addition of phytohormones not only helps to reduce production costs but also improves the efficiency of biofuel utilization. However, accurate and sensitive phytohormones determination and analytical methods are the basis for plant hormone research. In this study, the characteristics of phytohormones in microalgae and research progress for regulating the accumulation of energy storage substances in microalgae by exogenous phytohormones, combined with abiotic stress conditions at home and abroad, are summarized. The possible metabolic mechanism of phytohormones in microalgae is discussed, and possible future research directions are put forward, which provide a theoretical basis for the application of phytohormones in microalgae.

Comparative hormonal and metabolic profile analysis based on mass spectrometry provides information on the regulation of water-deficit stress response of sunflower (Helianthus annuus L.) inbred lines with different water-deficit stress sensitivity

Water-deficit stress is the most important abiotic stress restricting plant growth, development and yield. The effects of this stress, however, depend on genotypes, among other factors. This study assembles morpho-physiological and metabolic approaches to assess hormonal and metabolic profile changes, upon water-deficit stress, in the shoot and roots of two contrasting sunflower inbred lines, B59 (water-deficit stress sensitive) and B71 (water-deficit stress tolerant). The analyses were carried out using mass spectrometry and performing a multivariate statistical analysis to identify relationships between the analyzed variables. Water-deficit stress reduced all morpho-physiological parameters, except for root length in the tolerant inbred line. The hormonal pathways were active in mediating the seedling performance to imposed water-deficit stress in both lines, although with some differences between lines at the organ level. B59 displayed a diverse metabolite battery, including organic acids, organic compounds as well as sugars, mainly in the shoot, whereas B71 showed primary amino acids, organic acids and organic compounds predominantly in its roots. The discrimination between control and water-deficit stress conditions was possible thanks to potential biomarkers of stress treatment, e.g., proline, maleic acid and malonic acid. This study indicated that the studied organs of sunflower seedlings have different mechanisms of regulation under water-deficit stress. These findings could help to better understand the physio-biochemical pathways underlying stress tolerance in sunflower at early-growth stage.

Two-component signaling system in plants: interaction network and specificity in response to stress and hormones

Plants are exposed to various environmental challenges that can hamper their growth, development, and productivity. Being sedentary, plants cannot escape from these unfavorable environmental conditions and have evolved various signaling cascades to endure them. The two-component signaling (TCS) system is one such essential signaling circuitry present in plants regulating responses against multiple abiotic and biotic stresses. It is among the most ancient and evolutionary conserved signaling pathways in plants, which include membrane-bound histidine kinases (HKs), cytoplasmic histidine phosphotransfer proteins (Hpts), and nuclear or cytoplasmic response regulators (RRs). At the same time, TCS also involved in many signaling circuitries operative in plants in response to diverse hormones. These plant growth hormones play a significant role in diverse physiological and developmental processes, and their contribution to plant stress responses is coming up in a big way. Therefore, it is intriguing to know how TCS and various plant growth regulators, along with the key transcription factors, directly or indirectly control the responses of plants towards diverse stresses. The present review attempts to explore this relationship, hoping that this knowledge will contribute towards developing crop plants with enhanced climate resilience.