Chromatin modifications and memory in regulation of stress-related polyphenols: finding new ways to control flavonoid biosynthesis.

The influence of epigenetic factors on plant defense responses and the balance between growth and defense is becoming a central area in plant biology. It is believed that the biosynthesis of secondary metabolites can be regulated by epigenetic factors, but this is not associated with the formation of a "memory" to the previous biosynthetic status. This review shows that some epigenetic effects can result in epigenetic memory, which opens up new areas of research in secondary metabolites, in particular flavonoids. Plant-controlled chromatin modifications can lead to the generation of stress memory, a phenomenon through which information regarding past stress cues is retained, resulting in a modified response to recurring stress. How deeply are the mechanisms of chromatin modification and memory generation involved in the control of flavonoid biosynthesis? This article collects available information from the literature and interactome databases to address this issue. Visualization of the interaction of chromatin-modifying proteins with the flavonoid biosynthetic machinery is presented. Chromatin modifiers and "bookmarks" that may be involved in the regulation of flavonoid biosynthesis through memory have been identified. Through different mechanisms of chromatin modification, plants can harmonize flavonoid metabolism with: stress responses, developmental programs, light-dependent processes, flowering, and longevity programs. The available information points to the possibility of developing chromatin-modifying technologies to control flavonoid biosynthesis.

Isolation and Characterization of Extracellular Vesicles from Arabidopsis thaliana Cell Culture and Investigation of the Specificities of Their Biogenesis.

Over recent years, extracellular vesicles (EVs), commonly termed exosomes, have gained prominence for their potential as natural nanocarriers. It has now been recognized that plants also secrete EVs. Despite this discovery, knowledge about EV biogenesis in plant cell cultures remains limited. In our study, we have isolated and meticulously characterized EVs from the callus culture of the model plant, Arabidopsis thaliana. Our findings indicate that the abundance of EVs in calli was less than that in the plant's apoplastic fluid. This difference was associated with the transcriptional downregulation of the endosomal sorting complex required for transport (ESCRT) genes in the calli cells. While salicylic acid increased the expression of ESCRT components, it did not enhance EV production. Notably, EVs from calli contained proteins essential for cell wall biogenesis and defense mechanisms, as well as microRNAs consistent with those found in intact plants. This suggests that plant cell cultures could serve as a feasible source of EVs that reflect the characteristics of the parent plant species. However, further research is essential to determine the optimal conditions for efficient EV production in these cultured cells.

Proteome-Level Investigation of Vitis amurensis Calli Transformed with a Constitutively Active, Ca2+-Independent Form of the Arabidopsis AtCPK1 Gene.

Calcium-dependent protein kinases (CDPKs) are one of the main Ca2+ decoders in plants. Among them, Arabidopsis thaliana AtCPK1 is one of the most studied CDPK genes as a positive regulator of plant responses to biotic and abiotic stress. The mutated form of AtCPK1, in which the autoinhibitory domain is inactivated (AtCPK1-Ca), provides constitutive kinase activity by mimicking a stress-induced increase in the Ca2+ flux. In the present study, we performed a proteomic analysis of Vitis amurensis calli overexpressing the AtCPK1-Ca form using untransformed calli as a control. In our previous studies, we have shown that the overexpression of this mutant form leads to the activation of secondary metabolism in plant cell cultures, including an increase in resveratrol biosynthesis in V. amurensis cell cultures. We analyzed upregulated and downregulated proteins in control and transgenic callus cultures using two-dimensional gel electrophoresis, and Matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF). In calli transformed with AtCPK1-Ca, an increased amounts of pathogenesis-related proteins were found. A quantitative real-time PCR analysis confirmed this result.

Biosynthesis of Functional Silver Nanoparticles Using Callus and Hairy Root Cultures of Aristolochia manshuriensis.

This study delves into the novel utilization of Aristolochia manshuriensis cultured cells for extracellular silver nanoparticles (AgNPs) synthesis without the need for additional substances. The presence of elemental silver has been verified using energy-dispersive X-ray spectroscopy, while distinct surface plasmon resonance peaks were revealed by UV-Vis spectra. Transmission and scanning electron microscopy indicated that the AgNPs, ranging in size from 10 to 40 nm, exhibited a spherical morphology. Fourier-transform infrared analysis validated the abilty of A. manshuriensis extract components to serve as both reducing and capping agents for metal ions. In the context of cytotoxicity on embryonic fibroblast (NIH 3T3) and mouse neuroblastoma (N2A) cells, AgNPs demonstrated varying effects. Specifically, nanoparticles derived from callus cultures exhibited an IC50 of 2.8 µg/mL, effectively inhibiting N2A growth, whereas AgNPs sourced from hairy roots only achieved this only at concentrations of 50 µg/mL and above. Notably, all studied AgNPs' treatment-induced cytotoxicity in fibroblast cells, yielding IC50 values ranging from 7.2 to 36.3 µg/mL. Furthermore, the findings unveiled the efficacy of the synthesized AgNPs against pathogenic microorganisms impacting both plants and animals, including Agrobacterium rhizogenes, A. tumefaciens, Bacillus subtilis, and Escherichia coli. These findings underscore the effectiveness of biotechnological methodologies in offering advanced and enhanced green nanotechnology alternatives for generating nanoparticles with applications in combating cancer and infectious disorders.

Auxin-dependent regulation of growth via rolB-induced modulation of the ROS metabolism in the long-term cultivated pRiA4-transformed Rubiacordifolia L. calli.

Gene transfer from Agrobacterium to plants is the best studied example of horizontal gene transfer (HGT) between prokaryotes and eukaryotes. The rol genes of A. rhizogenes (Rhizobium rhizogenes) provide uncontrolled root growth, or "hairy root" syndrome, the main diagnostic feature. In the present study, we investigated the stable pRiA4-transformed callus culture of Rubia cordifolia L. While untransformed callus cultures need PGRs (plant growth regulators) as an obligatory supplement, pRiA4 calli is able to achieve long-term PGR-free cultivation. For the first time, we described the pRiA4-transformed callus cultures' PGR-dependent ROS status, growth, and specialized metabolism. As we have shown, expression of the rolA and rolB but not the rolC genes is contradictory in a PGR-dependent manner. Moreover, a PGR-free pRiA4 transformed cell line is characterised as more anthraquinone (AQ) productive than an untransformed cell culture. These findings pertain to actual plant biotechnology: it could be the solution to troubles in choosing the best PGR combination for the cultivation of some rare, medicinal, and woody plants; wild-type Ri-plants and tissue cultures may become freed from legal controls on genetically modified organisms in the future. We propose possible PGR-dependent relationships between rolA and rolB as well as ROS signalling targets. The present study highlighted the high importance of the rolA gene in the regulation of combined rol gene effects and the large knowledge gap in rolA action.

Enhanced Production of Nitrogenated Metabolites with Anticancer Potential in Aristolochia manshuriensis Hairy Root Cultures.

Aristolochia manshuriensis is a relic liana, which is widely used in traditional Chinese herbal medicine and is endemic to the Manchurian floristic region. Since this plant is rare and slow-growing, alternative sources of its valuable compounds could be explored. Herein, we established hairy root cultures of A. manshuriensis transformed with Agrobacterium rhizogenes root oncogenic loci (rol)B and rolC genes. The accumulation of nitrogenous secondary metabolites significantly improved in transgenic cell cultures. Specifically, the production of magnoflorine reached up to 5.72 mg/g of dry weight, which is 5.8 times higher than the control calli and 1.7 times higher than in wild-growing liana. Simultaneously, the amounts of aristolochic acids I and II, responsible for the toxicity of Aristolochia species, decreased by more than 10 fold. Consequently, the hairy root extracts demonstrated pronounced cytotoxicity against human glioblastoma cells (U-87 MG), cervical cancer cells (HeLa CCL-2), and colon carcinoma (RKO) cells. However, they did not exhibit significant activity against triple-negative breast cancer cells (MDA-MB-231). Our findings suggest that hairy root cultures of A. manshuriensis could be considered for the rational production of valuable A. manshuriensis compounds by the modification of secondary metabolism.

Suppression of the HOS1 Gene Affects the Level of ROS Depending on Light and Cold.

The E3 ubiquitin-protein ligase HOS1 is an important integrator of temperature information and developmental processes. HOS1 is a negative regulator of plant cold tolerance, and silencing HOS1 leads to increased cold tolerance. In the present work, we studied ROS levels in hos1Cas9Arabidopsis thaliana plants, in which the HOS1 gene was silenced by disruption of the open reading frame via CRISPR/Cas9 technology. Confocal imaging of intracellular reactive oxygen species (ROS) showed that the hos1 mutation moderately increased levels of ROS under both low and high light (HL) conditions, but wild-type (WT) and hos1Cas9 plants exhibited similar ROS levels in the dark. Visualization of single cells did not reveal differences in the intracellular distribution of ROS between WT and hos1Cas9 plants. The hos1Cas9 plants contained a high basal level of ascorbic acid, maintained a normal balance between reduced and oxidized glutathione (GSH and GSSG), and generated a strong antioxidant defense response against paraquat under HL conditions. Under cold exposure, the hos1 mutation decreased the ROS level and substantially increased the expression of the ascorbate peroxidase genes Apx1 and Apx2. When plants were pre-exposed to cold and further exposed to HL, the expression of the NADPH oxidase genes RbohD and RbohF was increased in the hos1Cas9 plants but not in WT plants. hos1-mediated changes in the level of ROS are cold-dependent and cold-independent, which implies different levels of regulation. Our data indicate that HOS1 is required to maintain ROS homeostasis not only under cold conditions, but also under conditions of both low and high light intensity. It is likely that HOS1 prevents the overinduction of defense mechanisms to balance growth.

Proteomic Analysis of Proteins Related to Defense Responses in Arabidopsis Plants Transformed with the rolB Oncogene.

During Agrobacterium rhizogenes-plant interaction, the rolB gene is transferred into the plant genome and is stably inherited in the plant's offspring. Among the numerous effects of rolB on plant metabolism, including the activation of secondary metabolism, its effect on plant defense systems has not been sufficiently studied. In this work, we performed a proteomic analysis of rolB-expressing Arabidopsis thaliana plants with particular focus on defense proteins. We found a total of 77 overexpressed proteins and 64 underexpressed proteins in rolB-transformed plants using two-dimensional gel electrophoresis and MALDI mass spectrometry. In the rolB-transformed plants, we found a reduced amount of scaffold proteins RACK1A, RACK1B, and RACK1C, which are known as receptors for activated C-kinase 1. The proteomic analysis showed that rolB could suppress the plant immune system by suppressing the RNA-binding proteins GRP7, CP29B, and CP31B, which action are similar to the action of type-III bacterial effectors. At the same time, rolB plants induce the massive biosynthesis of protective proteins VSP1 and VSP2, as well as pathogenesis-related protein PR-4, which are markers of the activated jasmonate pathway. The increased contents of glutathione-S-transferases F6, F2, F10, U19, and DHAR1 and the osmotin-like defense protein OSM34 were found. The defense-associated protein PCaP1, which is required for oligogalacturonide-induced priming and immunity, was upregulated. Moreover, rolB-transformed plants showed the activation of all components of the PYK10 defense complex that is involved in the metabolism of glucosinolates. We hypothesized that various defense systems activated by rolB protect the host plant from competing phytopathogens and created an effective ecological niche for A. rhizogenes. A RolB → RACK1A signaling module was proposed that might exert most of the rolB-mediated effects on plant physiology. Our proteomics data are available via ProteomeXchange with identifier PXD037959.

Effect of Stress Signals and Ib-rolB/C Overexpression on Secondary Metabolite Biosynthesis in Cell Cultures of Ipomoea batatas

Ipomoea batatas is a vital root crop and a source of caffeoylquinic acid derivatives (CQAs) with potential health-promoting benefits. As a naturally transgenic plant, I. batatas contains cellular T-DNA (cT-DNA) sequence homologs of the Agrobacterium rhizogenes open reading frame (ORF)14, ORF17n, rooting locus (Rol)B/RolC, ORF13, and ORF18/ORF17n of unknown function. This study aimed to evaluate the effect of abiotic stresses (temperature, ultraviolet, and light) and chemical elicitors (methyl jasmonate, salicylic acid, and sodium nitroprusside) on the biosynthesis of CQAs and cT-DNA gene expression in I. batatas cell culture as a model system. Among all the applied treatments, ultraviolet irradiation, methyl jasmonate, and salicylic acid caused the maximal accumulation of secondary compounds. We also discovered that I. batatas cT-DNA genes were not expressed in cell culture, and the studied conditions weakly affected their transcriptional levels. However, the Ib-rolB/C gene expressed under the strong 35S CaMV promoter increased the CQAs content by 1.5-1.9-fold. Overall, our results show that cT-DNA-encoded transgenes are not involved in stress- and chemical elicitor-induced CQAs accumulation in cell cultures of I. batatas. Nevertheless, overaccumulation of RolB/RolC transcripts potentiates the secondary metabolism of sweet potatoes through a currently unknown mechanism. Our study provides new insights into the molecular mechanisms linked with CQAs biosynthesis in cell culture of naturally transgenic food crops, i.e., sweet potato.

Callus Culture of Scorzonera radiata as a New, Highly Productive and Stable Source of Caffeoylquinic Acids.

During our ongoing efforts to investigate biotechnological sources of caffeoylquinic acid (CQA) metabolites, we discovered the plant Scorzonera radiata Fisch. (Asteraceae), which is able to produce callus cultures with high yield and extremely high stability. An actively growing callus line, designated as Sr-L1, retained the ability to produce 11 CQAs during long-term cultivation (more than 20 years). A total of 29 polyphenolic compounds were identified in the leaves and Sr-L1 callus culture of S. radiata, including CQAs, lignol derivatives, flavonoids, and dihydrostilbenes. The composition of CQAs in the Sr-L1 culture was identical to that in the S. radiata leaves. Sr-L1 calli did not produce flavonoids and dihydrostilbenes, but produced lignol derivatives, which were absent in leaves. The HPLC-UV-HRMS determination showed the presence of monoacyl derivatives of CQAs such as 5-CQA, 4-CQA, cis-5-CQA, and 5-O-p-coumaroylquinic acid in the Sr-L1 culture. Among diacyl derivatives, 3,4-diCQA, 3,5-diCQA, cis-3,5-diCQA, 4,5-diCQA, 3-O-p-coumaroyl-5-O-CQA, and 3-O-caffeoyl-5-O-p-coumaroylquinic acid were found. The content of 5-CQA reached 7.54 mg/g dry weight and the content of 3,5-diCQA was as high as 18.52 mg/g dry weight. 3,5-diCQA has been reported to be of high nutritional and pharmacological value, as it alleviates inflammatory pain, reverses memory impairment by preventing neuronal apoptosis, and counteracts excessive adipose tissue expansion, serving as an attractive treatment option for obesity. The high content of 3,5-diCQA and the exceptional stability of biosynthesis make callus cultures of S. radiata a promising source for the development of drugs and nutraceuticals.

The RolB/RolC homolog from sweet potato promotes early flowering and triggers premature leaf senescence in transgenic Arabidopsis thaliana plants.

Expression of the root oncogenic loci (rol) genes from Agrobacterium rhizogenes provokes multiple divergent effects on physiological properties in transgenic plants and cell cultures. Recently, the homolog of the rolB and rolC oncogenes, named Ib-rolB/C, has been identified in the genome of a naturally transgenic food crop, i.e. sweet potato. In this study, we revealed that the Ipomoea batatas genome contains two full-length copies of Ib-rolB/C. The expression level of Ib-rolB/C in leaves of sweet potato showed a clear age-dependent pattern and increased as leaves senesce. Moreover, dark-induced senescence strongly up-regulates transcription of the Ib-rolB/C gene. Though Ib-rolB/C shares homology with its counterparts in A. rhizogenes, this gene was not capable to induce hairy roots or tumors in kalanchoe and tobacco plants. The Ib-rolB/C gene induced early-flowering phenotype, altered leaf morphology, and promoted premature leaf senescence in transgenic Arabidopsis thaliana plants. At the same time, Ib-rolB/C did not affect root morphology and biomass. Our results suggest that Ib-RolB/RolC participates in both age- and dark-triggered leaf senescence programs.

ABA-Dependent Regulation of Calcium-Dependent Protein Kinase Gene GmCDPK5 in Cultivated and Wild Soybeans.

Calcium-dependent protein kinases (CDPKs) regulate plant development and stress responses. However, the interaction of these protein kinases with the abscisic acid (ABA) stress hormone signalling system has not been studied in detail. In Arabidopsis, AtCPK1 plays an important role in the acclimation of plants to environmental stresses. Phylogenetic and molecular analyses showed that, among 50 isoforms of Glycine max (L.) Merrill CDPKs, the GmCDPK27/GmCDPK48, GmCDPK5/GmCDPK24, and GmCDPK10/GmCDPK46 paralogous pairs were the isoforms most related to AtCDPK1. We investigated the expression of the corresponding six GmCDPKs genes during treatment with cold, heat, and salt stress. Wild soybean was the most resistant to stresses, and among the three cultivars studied (Sfera, Hodgson, and Hefeng25), Sfera was close to the wild type in terms of resistance. GmCDPK5 and GmCDPK10 were the most responsive to stress treatments, especially in wild soybean, compared with cultivars. Among the studied GmCDPK isoforms, only GmCDPK5 expression increased after treatment with abscisic acid (ABA) in a dose- and time-dependent manner. Targeted LC-MS/MS analysis of endogenous ABA levels showed that wild soybean and Sfera had nearly twice the ABA content of Hodgson and Hefeng25. An analysis of the expression of marker genes involved in ABA biosynthesis showed that GmNCED1-gene-encoding 9-cis-epoxycarotenoid dioxygenase 1 is induced to the greatest extent in wild soybean and Sfera under salt, cold, and heat exposure. Our data established a correlation between the induction of GmCDPK5 and ABA biosynthesis genes. GmCDPK5 is an interesting target for genetic and bioengineering purposes and can be used for genetic editing, overexpression, or as a marker gene in soybean varieties growing under unfavourable conditions.

Overexpression of the A4-rolB gene from the pRiA4 of Rhizobium rhizogenes modulates hormones homeostasis and leads to an increase of flavonoid accumulation and drought tolerance in Arabidopsis thaliana transgenic plants.

MAIN CONCLUSION: Increased flavonol accumulation and enhanced drought tolerance in A4-rolB-overexpressing plants can be explained by the cooperative action of the SA and ROS signalling pathways. Clarification of function of the A4-rolB plast gene from pRiA4 of Rhizobium rhizogenes will allow a better understanding of the biological principles of the natural transformation process and its use as a tool for plant bioengineering. In the present study, we investigated whether the overexpression of A4-rolB gene could regulate two important processes, flavonoid biosynthesis and drought tolerance. In addition, we investigated some aspects of the possible machinery of the A4-rolB-induced changes in plant physiology, such as crosstalk of the major signalling systems. Based on the data obtained in this work, it can be presumed that constitutive overexpression of A4-rolB leads to the activation of the salicylic acid signalling system. An increase in flavonol accumulation and enhanced drought tolerance can be explained by the cooperative action of SA and ROS pathways.

Biosynthesis and Cytotoxic Properties of Ag, Au, and Bimetallic Nanoparticles Synthesized Using Lithospermum erythrorhizon Callus Culture Extract.

The present study reports a green chemistry approach for the rapid and easy biological synthesis of silver (Ag), gold (Au), and bimetallic Ag/Au nanoparticles using the callus extract of Lithospermum erythrorhizon as a reducing and capping agent. The biosynthesized nanoparticles were characterized with ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD) analysis, and transmission electron microscopy (TEM). Our results showed the formation of crystalline metal nanostructures of both spherical and non-spherical shape. Energy dispersive X-ray (EDX) spectroscopy showed the characteristic peaks in the silver and gold regions, confirming the presence of the corresponding elements in the monometallic particles and both elements in the bimetallic particles. Fourier-transform infrared (FTIR) spectroscopy affirmed the role of polysaccharides and polyphenols of the L. erythrorhizon extract as the major reducing and capping agents for metal ions. In addition, our results showed that the polysaccharide sample and the fraction containing secondary metabolites isolated from L. erythrorhizon were both able to produce large amounts of metallic nanoparticles. The biosynthesized nanoparticles demonstrated cytotoxicity against mouse neuroblastoma and embryonic fibroblast cells, which was considerably higher for Ag nanoparticles and for bimetallic Ag/Au nanoparticles containing a higher molar ratio of silver. However, fibroblast migration was not significantly affected by any of the nanoparticles tested. The obtained results provide a new example of the safe biological production of metallic nanoparticles, but further study is required to uncover the mechanism of their toxicity so that the biomedical potency can be assessed.

Biomimetic synthesis of functional silver nanoparticles using hairy roots of Panax ginseng for wheat pathogenic fungi treatment.

Presently, multifunctional silver nanoparticles (AgNPs) show a rapid growth in various commercial applications, leading to increasing demand for new eco-friendly manufacturing technologies. An array of genetic engineering tools can be used to increase the yield in the production of AgNPs using various biological systems. The present study reports a green chemistry approach for the biological synthesis of AgNPs using extracts from non-transformed callus, rolC-transgenic callus and hairy roots of Panax ginseng and an evaluation of their efficacy against crop-damaging fungal pathogens. All types of ginseng cell lines promote the reduction of silver nitrate and formation of spherical AgNPs with an average diameter of 50-90 nm. Notably, hairy root extract possessed the maximal reduction potential among the studied cell lines probably due to higher secondary metabolite content. The biosynthesized nanoparticles were highly toxic against several wheat fungal pathogens including Fusarium graminearum, F. avenaceum, F. poae, and F. sporotrichioides, which are associated with fusarium head blight disease in cereals. Furthermore, the antifungal activity of nanosilver was successfully utilized for surface sterilization of infected wheat kernels without any negative effect on seed germination capability.

A Brief Overview of Potential Treatments for Viral Diseases Using Natural Plant Compounds: The Case of SARS-Cov.

The COVID-19 pandemic, as well as the more general global increase in viral diseases, has led researchers to look to the plant kingdom as a potential source for antiviral compounds. Since ancient times, herbal medicines have been extensively applied in the treatment and prevention of various infectious diseases in different traditional systems. The purpose of this review is to highlight the potential antiviral activity of plant compounds as effective and reliable agents against viral infections, especially by viruses from the coronavirus group. Various antiviral mechanisms shown by crude plant extracts and plant-derived bioactive compounds are discussed. The understanding of the action mechanisms of complex plant extract and isolated plant-derived compounds will help pave the way towards the combat of this life-threatening disease. Further, molecular docking studies, in silico analyses of extracted compounds, and future prospects are included. The in vitro production of antiviral chemical compounds from plants using molecular pharming is also considered. Notably, hairy root cultures represent a promising and sustainable way to obtain a range of biologically active compounds that may be applied in the development of novel antiviral agents.

CRISPR/Cas9-Mediated Knockout of HOS1 Reveals Its Role in the Regulation of Secondary Metabolism in Arabidopsis thaliana.

In Arabidopsis, the RING finger-containing E3 ubiquitin ligase HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 1 (HOS1) functions as a main regulator of the cold signaling. In this study, CRISPR/Cas9-mediated targeted mutagenesis of the HOS1 gene in the first exon was performed. DNA sequencing showed that frameshift indels introduced by genome editing of HOS1 resulted in the appearance of premature stop codons, disrupting the open reading frame. Obtained hos1 Cas9 mutant plants were compared with the SALK T-DNA insertion mutant, line hos1-3, in terms of their tolerance to abiotic stresses, accumulation of secondary metabolites and expression levels of genes participating in these processes. Upon exposure to cold stress, enhanced tolerance and expression of cold-responsive genes were observed in both hos1-3 and hos1 Cas9 plants. The hos1 mutation caused changes in the synthesis of phytoalexins in transformed cells. The content of glucosinolates (GSLs) was down-regulated by 1.5-times, while flavonol glycosides were up-regulated by 1.2 to 4.2 times in transgenic plants. The transcript abundance of the corresponding MYB and bHLH transcription factors, which are responsible for the regulation of secondary metabolism in Arabidopsis, were also altered. Our data suggest a relationship between HOS1-regulated downstream signaling and phytoalexin biosynthesis.

Basic Protein Modules Combining Abscisic Acid and Light Signaling in Arabidopsis.

It is generally accepted that plants use the complex signaling system regulated by light and abscisic acid (ABA) signaling components to optimize growth and development in different situations. The role of ABA-light interactions is evident in the coupling of stress defense reactions with seed germination and root development, maintaining of stem cell identity and stem cell specification, stem elongation and leaf development, flowering and fruit formation, senescence, and shade avoidance. All these processes are regulated jointly by the ABA-light signaling system. Although a lot of work has been devoted to ABA-light signal interactions, there is still no systematic description of central signaling components and protein modules, which jointly regulate plant development. New data have emerged to promote understanding of how ABA and light signals are integrated at the molecular level, representing an extensively growing area of research. This work is intended to fill existing gaps by using literature data combined with bioinformatics analysis.

Linking Brassinosteroid and ABA Signaling in the Context of Stress Acclimation.

The important regulatory role of brassinosteroids (BRs) in the mechanisms of tolerance to multiple stresses is well known. Growing data indicate that the phenomenon of BR-mediated drought stress tolerance can be explained by the generation of stress memory (the process known as 'priming' or 'acclimation'). In this review, we summarize the data on BR and abscisic acid (ABA) signaling to show the interconnection between the pathways in the stress memory acquisition. Starting from brassinosteroid receptors brassinosteroid insensitive 1 (BRI1) and receptor-like protein kinase BRI1-like 3 (BRL3) and propagating through BR-signaling kinases 1 and 3 (BSK1/3) → BRI1 suppressor 1 (BSU1) -‖ brassinosteroid insensitive 2 (BIN2) pathway, BR and ABA signaling are linked through BIN2 kinase. Bioinformatics data suggest possible modules by which BRs can affect the memory to drought or cold stresses. These are the BIN2 → SNF1-related protein kinases (SnRK2s) → abscisic acid responsive elements-binding factor 2 (ABF2) module; BRI1-EMS-supressor 1 (BES1) or brassinazole-resistant 1 protein (BZR1)-TOPLESS (TPL)-histone deacetylase 19 (HDA19) repressor complexes, and the BZR1/BES1 → flowering locus C (FLC)/flowering time control protein FCA (FCA) pathway. Acclimation processes can be also regulated by BR signaling associated with stress reactions caused by an accumulation of misfolded proteins in the endoplasmic reticulum.

Coordination of ABA and Chaperone Signaling in Plant Stress Responses.

The abscisic acid (ABA) and chaperone signaling pathways are the central regulators of plant stress defense. Despite their significance and potential overlap, these systems have been described separately. In this review, we summarize information about mechanisms by which the ABA and chaperone signaling pathways might be coregulated. The central factors that join the ABA and chaperone signaling systems are the SWI/SNF chromatin-remodeling proteins, which are involved in stress memory. A benefit from coordination is that the signals sensed through both the ABA and chaperone signaling systems are perceived and stored via chromatin-remodeling factors. For improving plant stress resistance, we propose new bioengineering strategies, which we term 'bioengineering memory'.