Jasmonic acid perception by COI1 involves inositol polyphosphates in Arabidopsis thaliana

Genetic interaction between TTG2 and AtPLC1 reveals a role for phosphoinositide signaling in a co-regulated suite of Arabidopsis epidermal pathways

The TTG2 transcription factor of Arabidopsis regulates a set of epidermal traits, including the differentiation of leaf trichomes, flavonoid pigment production in cells of the inner testa (or seed coat) layer and mucilage production in specialized cells of the outer testa layer. Despite the fact that TTG2 has been known for over twenty years as an important regulator of multiple developmental pathways, little has been discovered about the downstream mechanisms by which TTG2 co-regulates these epidermal features. In this study, we present evidence of phosphoinositide lipid signaling as a mechanism for the regulation of TTG2-dependent epidermal pathways. Overexpression of the AtPLC1 gene rescues the trichome and seed coat phenotypes of the ttg2-1 mutant plant. Moreover, in the case of seed coat color rescue, AtPLC1 overexpression restored expression of the TTG2 flavonoid pathway target genes, TT12 and TT13/AHA10. Consistent with these observations, a dominant AtPLC1 T-DNA insertion allele (plc1-1D) promotes trichome development in both wild-type and ttg2-3 plants. Also, AtPLC1 promoter:GUS analysis shows expression in trichomes and this expression appears dependent on TTG2. Taken together, the discovery of a genetic interaction between TTG2 and AtPLC1 suggests a role for phosphoinositide signaling in the regulation of trichome development, flavonoid pigment biosynthesis and the differentiation of mucilage-producing cells of the seed coat. This finding provides new avenues for future research at the intersection of the TTG2-dependent developmental pathways and the numerous molecular and cellular phenomena influenced by phospholipid signaling.

Dynamic interactions between SPX proteins, the ubiquitination machinery, and signalling molecules for stress adaptation at a whole-plant level

The plant macronutrient phosphorus is a scarce resource and plant-available phosphate is limiting in most soil types. Generally, a gene regulatory module called the phosphate starvation response (PSR) enables efficient phosphate acquisition by roots and translocation to other organs. Plants growing on moderate to nutrient-rich soils need to co-ordinate availability of different nutrients and repress the highly efficient PSR to adjust phosphate acquisition to the availability of other macro- and micronutrients, and in particular nitrogen. PSR repression is mediated by a small family of single SYG1/Pho81/XPR1 (SPX) domain proteins. The SPX domain binds higher order inositol pyrophosphates that signal cellular phosphorus status and modulate SPX protein interaction with PHOSPHATE STARVATION RESPONSE1 (PHR1), the central transcriptional regulator of PSR. Sequestration by SPX repressors restricts PHR1 access to PSR gene promoters. Here we focus on SPX4 that primarily acts in shoots and sequesters many transcription factors other than PHR1 in the cytosol to control processes beyond the classical PSR, such as nitrate, auxin, and jasmonic acid signalling. Unlike SPX1 and SPX2, SPX4 is subject to proteasomal degradation not only by singular E3 ligases, but also by SCF-CRL complexes. Emerging models for these different layers of control and their consequences for plant acclimation to the environment will be discussed.

Deciphering the mechanisms, hormonal signaling, and potential applications of endophytic microbes to mediate stress tolerance in medicinal plants

The global healthcare market in the post-pandemic era emphasizes a constant pursuit of therapeutic, adaptogenic, and immune booster drugs. Medicinal plants are the only natural resource to meet this by supplying an array of bioactive secondary metabolites in an economic, greener and sustainable manner. Driven by the thrust in demand for natural immunity imparting nutraceutical and life-saving plant-derived drugs, the acreage for commercial cultivation of medicinal plants has dramatically increased in recent years. Limited resources of land and water, low productivity, poor soil fertility coupled with climate change, and biotic (bacteria, fungi, insects, viruses, nematodes) and abiotic (temperature, drought, salinity, waterlogging, and metal toxicity) stress necessitate medicinal plant productivity enhancement through sustainable strategies. Plants evolved intricate physiological (membrane integrity, organelle structural changes, osmotic adjustments, cell and tissue survival, reclamation, increased root-shoot ratio, antibiosis, hypersensitivity, etc.), biochemical (phytohormones synthesis, proline, protein levels, antioxidant enzymes accumulation, ion exclusion, generation of heat-shock proteins, synthesis of allelochemicals. etc.), and cellular (sensing of stress signals, signaling pathways, modulating expression of stress-responsive genes and proteins, etc.) mechanisms to combat stresses. Endophytes, colonizing in different plant tissues, synthesize novel bioactive compounds that medicinal plants can harness to mitigate environmental cues, thus making the agroecosystems self-sufficient toward green and sustainable approaches. Medicinal plants with a host set of metabolites and endophytes with another set of secondary metabolites interact in a highly complex manner involving adaptive mechanisms, including appropriate cellular responses triggered by stimuli received from the sensors situated on the cytoplasm and transmitting signals to the transcriptional machinery in the nucleus to withstand a stressful environment effectively. Signaling pathways serve as a crucial nexus for sensing stress and establishing plants' proper molecular and cellular responses. However, the underlying mechanisms and critical signaling pathways triggered by endophytic microbes are meager. This review comprehends the diversity of endophytes in medicinal plants and endophyte-mediated plant-microbe interactions for biotic and abiotic stress tolerance in medicinal plants by understanding complex adaptive physiological mechanisms and signaling cascades involving defined molecular and cellular responses. Leveraging this knowledge, researchers can design specific microbial formulations that optimize plant health, increase nutrient uptake, boost crop yields, and support a resilient, sustainable agricultural system.

ITPK1 Regulates Jasmonate-Controlled Root Development in Arabidopsis thaliana

Jasmonic acid (JA) is a plant hormone that regulates a plethora of physiological processes including immunity and development and is perceived by the F-Box protein, Coronatine-insensitive protein 1 (COI1). The discovery of inositol phosphates (InsPs) in the COI1 receptor complex highlights their role in JAperception. InsPs are phosphate-rich signaling molecules that control many aspects of plant physiology. Inositol pyrophosphates (PP-InsPs) are diphosphate containing InsP species, of which InsP7 and InsP8 are the best characterized ones. Different InsP and PP-InsP species are linked with JA-related plant immunity. However, role of PP-InsP species in regulating JA-dependent developmental processes are poorly understood. Recent identification of ITPK1 kinase, responsible for the production of 5-InsP7 from InsP6in planta, provides a platform to investigate the possible involvement of ITPK-derived InsP species in JA-related plant development. Here, in this study, we report that ITPK1-defective plants exhibit increased root growth inhibition to bioactive JA treatment. The itpk1 plants also show increased lateral root density when treated with JA. Notably, JA treatment does not increase ITPK1 protein levels. Gene expression analyses revealed that JA-biosynthetic genes are not differentially expressed in ITPK1-deficient plants. We further demonstrate that genes encoding different JAZ repressor proteins are severely down-regulated in ITPK1-defective plants. Taken together, our study highlights the role of ITPK1 in regulating JA-dependent root architecture development through controlling the expression of different JAZ repressor proteins.

Jasmonic Acid as a Mediator in Plant Response to Necrotrophic Fungi

Jasmonic acid (JA) and its derivatives, all named jasmonates, are the simplest phytohormones which regulate multifarious plant physiological processes including development, growth and defense responses to various abiotic and biotic stress factors. Moreover, jasmonate plays an important mediator's role during plant interactions with necrotrophic oomycetes and fungi. Over the last 20 years of research on physiology and genetics of plant JA-dependent responses to pathogens and herbivorous insects, beginning from the discovery of the JA co-receptor CORONATINE INSENSITIVE1 (COI1), research has speeded up in gathering new knowledge on the complexity of plant innate immunity signaling. It has been observed that biosynthesis and accumulation of jasmonates are induced specifically in plants resistant to necrotrophic fungi (and also hemibiotrophs) such as mostly investigated model ones, i.e., Botrytis cinerea, Alternaria brassicicola or Sclerotinia sclerotiorum. However, it has to be emphasized that the activation of JA-dependent responses takes place also during susceptible interactions of plants with necrotrophic fungi. Nevertheless, many steps of JA function and signaling in plant resistance and susceptibility to necrotrophs still remain obscure. The purpose of this review is to highlight and summarize the main findings on selected steps of JA biosynthesis, perception and regulation in the context of plant defense responses to necrotrophic fungal pathogens.

Jasmonate perception: Ligand-receptor interaction, regulation, and evolution

Phytohormones integrate external environmental and developmental signals with internal cellular responses for plant survival and multiplication in changing surroundings. Jasmonate (JA), which might originate from prokaryotes and benefit plant terrestrial adaptation, is a vital phytohormone that regulates diverse developmental processes and defense responses against various environmental stresses. In this review, we first provide an overview of ligand-receptor binding techniques used for the characterization of phytohormone-receptor interactions, then introduce the identification of the receptor COI1 and active JA molecules, and finally summarize recent advances on the regulation of JA perception and its evolution.

OsWRKY76 positively regulates drought stress via OsbHLH148-mediated jasmonate signaling in rice

Drought stress is a major environmental threat that limits plant growth and crop productivity. Therefore, it is necessary to uncover the molecular mechanisms behind drought tolerance in crops. Here, OsWRKY76 positively regulated drought stress in rice. OsWRKY76 expression was induced by PEG treatment, dehydration stress, and exogenous MeJA rather than by no treatment. Notably, OsWRKY76 knockout weakened drought tolerance at the seedling stage and decreased MeJA sensitivity. OsJAZ12 was significantly induced by drought stress, and its expression was significantly higher in OsWRKY76-knockout mutants than in wild-type ZH11 under drought stress. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that OsWRKY76 interacted with OsJAZ12. OsWRKY76 weakened the interaction between OsbHLH148 and OsJAZ12 in yeast cells. The OsJAZ12 protein repressed the transactivation activity of OsbHLH148, and this repression was partly restored by OsWRKY76 in rice protoplasts. Moreover, OsDREB1E expression was lower in OsWRKY76-knockout mutants than in wild-type ZH11 under drought stress, but it was upregulated under normal growth conditions. Yeast one-hybrid, electrophoretic mobility shift, and dual-luciferase assays showed that OsWRKY76 and OsbHLH148 bound directly to the OsDREB1E promoter and activated OsDREB1E expression in response to drought stress. These results suggest that OsWRKY76 confers drought tolerance through OsbHLH148-mediated jasmonate signaling in rice, offering a new clue to uncover the mechanisms behind drought tolerance.

Roles of plastid-located phosphate transporters in carotenoid accumulation

Enhanced carotenoid accumulation in plants is crucial for the nutritional and health demands of the human body since these beneficial substances are acquired through dietary intake. Plastids are the major organelles to accumulate carotenoids in plants and it is reported that manipulation of a single plastid phosphate transporter gene enhances carotenoid accumulation. Amongst all phosphate transport proteins including phosphate transporters (PHTs), plastidial phosphate translocators (pPTs), PHOSPHATE1 (PHO1), vacuolar phosphate efflux transporter (VPE), and Sulfate transporter [SULTR]-like phosphorus distribution transporter (SPDT) in plants, plastidic PHTs (PHT2 & PHT4) are found as the only clade that is plastid located, and manipulation of which affects carotenoid accumulation. Manipulation of a single chromoplast PHT (PHT4;2) enhances carotenoid accumulation, whereas manipulation of a single chloroplast PHT has no impact on carotenoid accumulation. The underlying mechanism is mainly attributed to their different effects on plastid orthophosphate (Pi) concentration. PHT4;2 is the only chromoplast Pi efflux transporter, and manipulating this single chromoplast PHT significantly regulates chromoplast Pi concentration. This variation subsequently modulates the carotenoid accumulation by affecting the supply of glyceraldehyde 3-phosphate, a substrate for carotenoid biosynthesis, by modulating the transcript abundances of carotenoid biosynthesis limited enzyme genes, and by regulating chromoplast biogenesis (facilitating carotenoid storage). However, at least five orthophosphate influx PHTs are identified in the chloroplast, and manipulating one of the five does not substantially modulate the chloroplast Pi concentration in a long term due to their functional redundancy. This stable chloroplast Pi concentration upon one chloroplast PHT absence, therefore, is unable to modulate Pi-involved carotenoid accumulation processes and finally does affect carotenoid accumulation in photosynthetic tissues. Despite these advances, several cases including the precise location of plastid PHTs, the phosphate transport direction mediated by these plastid PHTs, the plastid PHTs participating in carotenoid accumulation signal pathway, the potential roles of these plastid PHTs in leaf carotenoid accumulation, and the roles of these plastid PHTs in other secondary metabolites are waiting for further research. The clarification of the above-mentioned cases is beneficial for breeding high-carotenoid accumulation plants (either in photosynthetic or non-photosynthetic edible parts of plants) through the gene engineering of these transporters.

Jasmonates in plant growth and development and elicitation of secondary metabolites: An updated overview

Secondary metabolites are incontestably key specialized molecules with proven health-promoting effects on human beings. Naturally synthesized secondary metabolites are considered an important source of pharmaceuticals, food additives, cosmetics, flavors, etc., Therefore, enhancing the biosynthesis of these relevant metabolites by maintaining natural authenticity is getting more attention. The application of exogenous jasmonates (JAs) is well recognized for its ability to trigger plant growth and development. JAs have a large spectrum of action that covers seed germination, hypocotyl growth regulation, root elongation, petal expansion, and apical hook growth. This hormone is considered as one of the key regulators of the plant's growth and development when the plant is under biotic or abiotic stress. The JAs regulate signal transduction through cross-talking with other genes in plants and thereby deploy an appropriate metabolism in the normal or stressed conditions. It has also been found to be an effective chemical elicitor for the synthesis of naturally occurring secondary metabolites. This review discusses the significance of JAs in the growth and development of plants and the successful outcomes of jasmonate-driven elicitation of secondary metabolites including flavonoids, anthraquinones, anthocyanin, xanthonoid, and more from various plant species. However, as the enhancement of these metabolites is essentially measured via in vitro cell culture or foliar spray, the large-scale production is significantly limited. Recent advancements in the plant cell culture technology lay the possibilities for the large-scale manufacturing of plant-derived secondary metabolites. With the insights about the genetic background of the metabolite biosynthetic pathway, synthetic biology also appears to be a potential avenue for accelerating their production. This review, therefore, also discussed the potential manoeuvres that can be deployed to synthesis plant secondary metabolites at the large-scale using plant cell, tissue, and organ cultures.

Local and systemic responses conferring acclimation of Brassica napus roots to low phosphorus conditions

Due to the non-uniform distribution of inorganic phosphate (Pi) in the soil, plants modify their root architecture to improve acquisition of this nutrient. In this study, a split-root system was employed to assess the nature of local and systemic signals that modulate root architecture of Brassica napus grown with non-uniform Pi availability. Lateral root (LR) growth was regulated systemically by non-uniform Pi distribution, by increasing the second-order LR (2°LR) density in compartments with high Pi supply but decreasing it in compartments with low Pi availability. Transcriptomic profiling identified groups of genes regulated, both locally and systemically, by Pi starvation. The number of systemically induced genes was greater than the number of genes locally induced, and included genes related to abscisic acid (ABA) and jasmonic acid (JA) signalling pathways, reactive oxygen species (ROS) metabolism, sucrose, and starch metabolism. Physiological studies confirmed the involvement of ABA, JA, sugars, and ROS in the systemic Pi starvation response. Our results reveal the mechanistic basis of local and systemic responses of B. napus to Pi starvation and provide new insights into the molecular and physiological basis of root plasticity.

Investigation of the JASMONATE ZIM-DOMAIN Gene Family Reveals the Canonical JA-Signaling Pathway in Pineapple

JASMONATE ZIM-DOMAIN (JAZ) proteins are negative regulators of the jasmonate (JA)-signaling pathway and play pivotal roles in plant resistance to biotic and abiotic stresses. Genome-wide identification of JAZ genes has been performed in many plant species. However, systematic information about pineapple (Ananas comosus L. Merr.) JAZ genes (AcJAZs) is still not available. In this study, we identified 14 AcJAZ genes and classified them into five groups along with the Arabidopsis and rice orthologs. The AcJAZ genes have 3–10 exons, and the putative AcJAZ proteins have between two and eight conserved regions, including the TIFY motif and Jas domain. The cis-acting element analysis revealed that the putative promoter regions of AcJAZs contain between three and eight abiotic stress-responsive cis-acting elements. The gene-expression analysis suggested that AcJAZs were expressed differentially during plant development and subjected to regulation by the cold, heat, salt, and osmotic stresses as well as by phytohormones. Moreover, the BiFC analysis of protein interactions among the central JA-signaling regulators showed that AcJAZ4, AcMYC2, AcNINJA, and AcJAM1 could interact with AcJAZ5 and AcJAZ13 in vivo, indicating a canonical JA-signaling pathway in pineapple. These results increase our understanding of the functions of AcJAZs and the responses of the core players in the JA-signaling pathway to abiotic stresses.

Salicylic Acid in Root Growth and Development

In plants, salicylic acid (SA) is a hormone that mediates a plant’s defense against pathogens. SA also takes an active role in a plant’s response to various abiotic stresses, including chilling, drought, salinity, and heavy metals. In addition, in recent years, numerous studies have confirmed the important role of SA in plant morphogenesis. In this review, we summarize data on changes in root morphology following SA treatments under both normal and stress conditions. Finally, we provide evidence for the role of SA in maintaining the balance between stress responses and morphogenesis in plant development, and also for the presence of SA crosstalk with other plant hormones during this process.

S-Nitrosation of E3 Ubiquitin Ligase Complex Components Regulates Hormonal Signalings in Arabidopsis

E3 ubiquitin ligases mediate the last step of the ubiquitination pathway in the ubiquitin-proteasome system (UPS). By targeting transcriptional regulators for their turnover, E3s play a crucial role in every aspect of plant biology. In plants, SKP1/CULLIN1/F-BOX PROTEIN (SCF)-type E3 ubiquitin ligases are essential for the perception and signaling of several key hormones including auxins and jasmonates (JAs). F-box proteins, TRANSPORT INHIBITOR RESPONSE 1 (TIR1) and CORONATINE INSENSITIVE 1 (COI1), bind directly transcriptional repressors AUXIN/INDOLE-3-ACETIC ACID (AUX/IAA) and JASMONATE ZIM-DOMAIN (JAZ) in auxin- and JAs-depending manner, respectively, which permits the perception of the hormones and transcriptional activation of signaling pathways. Redox modification of proteins mainly by S-nitrosation of cysteines (Cys) residues via nitric oxide (NO) has emerged as a valued regulatory mechanism in physiological processes requiring its rapid and versatile integration. Previously, we demonstrated that TIR1 and Arabidopsis thaliana SKP1 (ASK1) are targets of S-nitrosation, and these NO-dependent posttranslational modifications enhance protein-protein interactions and positively regulate SCFTIR1 complex assembly and expression of auxin response genes. In this work, we confirmed S-nitrosation of Cys140 in TIR1, which was associated in planta to auxin-dependent developmental and stress-associated responses. In addition, we provide evidence on the modulation of the SCFCOI1 complex by different S-nitrosation events. We demonstrated that S-nitrosation of ASK1 Cys118 enhanced ASK1-COI1 protein-protein interaction. Overexpression of non-nitrosable ask1 mutant protein impaired the activation of JA-responsive genes mediated by SCFCOI1 illustrating the functional relevance of this redox-mediated regulation in planta. In silico analysis positions COI1 as a promising S-nitrosation target, and demonstrated that plants treated with methyl JA (MeJA) or S-nitrosocysteine (NO-Cys, S-nitrosation agent) develop shared responses at a genome-wide level. The regulation of SCF components involved in hormonal perception by S-nitrosation may represent a key strategy to determine the precise time and site-dependent activation of each hormonal signaling pathway and highlights NO as a pivotal molecular player in these scenarios.

Arabidopsis inositol polyphosphate kinases IPK1 and ITPK1 modulate crosstalk between SA-dependent immunity and phosphate-starvation responses

KEY MESSAGE

Selective Arabidopsis thaliana inositol phosphate kinase functions modulate response amplitudes in innate immunity by balancing signalling adjustments with phosphate homeostasis networks. Pyrophosphorylation of InsP6 generates InsP7 and/or InsP8 containing high-energy phosphoanhydride bonds that are harnessed during energy requirements of a cell. As bona fide co-factors for several phytohormone networks, InsP7/InsP8 modulate key developmental processes. With requirements in transducing jasmonic acid (JA) and phosphate-starvation responses (PSR), InsP8 exemplifies a versatile metabolite for crosstalks between different cellular pathways during diverse stress exposures. Here we show that Arabidopsis thaliana INOSITOL PENTAKISPHOSPHATE 2-KINASE 1 (IPK1), INOSITOL 1,3,4-TRISPHOSPHATE 5/6-KINASE 1 (ITPK1), and DIPHOSPHOINOSITOL PENTAKISPHOSPHATE KINASE 2 (VIH2) implicated in InsP8 biosynthesis, suppress salicylic acid (SA)-dependent immunity. In ipk1, itpk1 or vih2 mutants, constitutive activation of defenses lead to enhanced resistance against the Pseudomonas syringae pv tomato DC3000 (PstDC3000) strain. Our data reveal that upregulated SA-signaling sectors potentiate increased expression of several phosphate-starvation inducible (PSI)-genes, previously known in these mutants. In reciprocation, upregulated PSI-genes moderate expression amplitudes of defense-associated markers. We demonstrate that SA is induced in phosphate-deprived plants, however its defense-promoting functions are likely diverted to PSR-supportive roles. Overall, our investigations reveal selective InsPs as crosstalk mediators in defense-phosphate homeostasis and in reprogramming stress-appropriate response intensities.

Regulation of plant biotic interactions and abiotic stress responses by inositol polyphosphates

Inositol pyrophosphates (PP-InsPs), derivatives of inositol hexakisphosphate (phytic acid, InsP₆) or lower inositol polyphosphates, are energy-rich signaling molecules that have critical regulatory functions in eukaryotes. In plants, the biosynthesis and the cellular targets of these messengers are not fully understood. This is because, in part, plants do not possess canonical InsP₆ kinases and are able to synthesize PP-InsP isomers that appear to be absent in yeast or mammalian cells. This review will shed light on recent discoveries in the biosynthesis of these enigmatic messengers and on how they regulate important physiological processes in response to abiotic and biotic stresses in plants.

The interface of central metabolism with hormone signaling in plants

Amongst the myriad of metabolites produced by plants, primary metabolites and hormones play crucial housekeeping roles in the cell and are essential for proper plant growth and development. While the biosynthetic pathways of primary metabolism are well characterized, those of hormones are yet to be completely defined. Central metabolism provides precursors for hormone biosynthesis and the regulation and function of primary metabolites and hormones are tightly entwined. The combination of reverse genetics and technological advances in our ability to evaluate the levels of the molecular entities of the cell (transcripts, proteins and metabolites) has led to considerable improvements in our understanding of both the regulatory interaction between primary metabolites and hormones and its coordination in response to different conditions. Here, we provide an overview of the interaction of primary and hormone metabolism at the metabolic and signaling levels, as well as a perspective regarding the tools that can be used to tackle our current knowledge gaps at the signaling level.

Genome-Wide Identification and Expression Analysis of JAZ Family Involved in Hormone and Abiotic Stress in Sweet Potato and Its Two Diploid Relatives

Jasmonate ZIM-domain (JAZ) proteins are key repressors of a jasmonic acid signaling pathway. They play essential roles in the regulation of plant growth and development, as well as environmental stress responses. However, this gene family has not been explored in sweet potato. In this study, we identified 14, 15, and 14 JAZs in cultivated hexaploid sweet potato (Ipomoea batatas, 2n = 6x = 90), and its two diploid relatives Ipomoea trifida (2n = 2x = 30) and Ipomoea triloba (2n = 2x = 30), respectively. These JAZs were divided into five subgroups according to their phylogenetic relationships with Arabidopsis. The protein physiological properties, chromosome localization, phylogenetic relationship, gene structure, promoter cis-elements, protein interaction network, and expression pattern of these 43 JAZs were systematically investigated. The results suggested that there was a differentiation between homologous JAZs, and each JAZ gene played different vital roles in growth and development, hormone crosstalk, and abiotic stress response between sweet potato and its two diploid relatives. Our work provided comprehensive comparison and understanding of the JAZ genes in sweet potato and its two diploid relatives, supplied a theoretical foundation for their functional study, and further facilitated the molecular breeding of sweet potato.

Function and Mechanism of Jasmonic Acid in Plant Responses to Abiotic and Biotic Stresses

As sessile organisms, plants must tolerate various environmental stresses. Plant hormones play vital roles in plant responses to biotic and abiotic stresses. Among these hormones, jasmonic acid (JA) and its precursors and derivatives (jasmonates, JAs) play important roles in the mediation of plant responses and defenses to biotic and abiotic stresses and have received extensive research attention. Although some reviews of JAs are available, this review focuses on JAs in the regulation of plant stress responses, as well as JA synthesis, metabolism, and signaling pathways. We summarize recent progress in clarifying the functions and mechanisms of JAs in plant responses to abiotic stresses (drought, cold, salt, heat, and heavy metal toxicity) and biotic stresses (pathogen, insect, and herbivore). Meanwhile, the crosstalk of JA with various other plant hormones regulates the balance between plant growth and defense. Therefore, we review the crosstalk of JAs with other phytohormones, including auxin, gibberellic acid, salicylic acid, brassinosteroid, ethylene, and abscisic acid. Finally, we discuss current issues and future opportunities in research into JAs in plant stress responses.

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

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

The jasmonoyl-isoleucine receptor CORONATINE INSENSITIVE1 suppresses defense gene expression in Arabidopsis roots independently of its ligand

The F-box protein CORONANTINE INSENSITIVE1 (COI1) serves as the receptor for the plant hormone jasmonoyl-isoleucine (JA-Ile). COI1, its co-receptors of the JASMONATE ZIM-domain (JAZ) protein family, and JA-Ile form a functional unit that regulates growth or defense mechanisms in response to various stress cues. Strikingly, COI1, but not JA-Ile, is required for susceptibility of Arabidopsis thaliana towards the soil-borne vascular pathogen Verticillium longisporum. In order to obtain marker genes for further analysis of this JA-Ile-independent COI1 function, transcriptome analysis of roots of coi1 and allene oxide synthase (aos) plants (impaired in JA biosynthesis) was performed. Intriguingly, nearly all of the genes that are differentially expressed in coi1 versus aos and wild type are constitutively more highly expressed in coi1. To support our notion that COI1 acts independently of its known downstream signaling components, coi1 plants were complemented with a COI1 variant (COI1_AA ) that is compromised in its interaction with JAZs. As expected, these plants showed only weak induction of the expression of the JA-Ile marker gene VEGETATIVE STORAGE PROTEIN2 after wounding and remained sterile. On the other hand, genes affected by COI1 but not by JA-Ile were still strongly repressed by COI1_AA . We suggest that COI1 has a potential moonlighting function that serves to repress gene expression in a JA-Ile- and JAZ-independent manner.

Phosphoinositide-specific phospholipase C gene involved in heat and drought tolerance in wheat (Triticum aestivum L.)

BACKGROUND

Phosphoinositide-specific phospholipase C proteins mediate environmental stress responses in many plants. However, the potential of PI-PLC genes involved with abiotic stress tolerance in wheat remains un-explored.

OBJECTIVE

To study TaPLC1 genetic relation with wheat drought and heat resistance.

METHODS

The seedlings were treated with PI-PLC inhibitor U73122 at the single leaf stage. The seedlings were treated with drought and heat stress at the two leaf stage, and some physiological indexes and the expression profile of TaPLC1 gene were determined. And the TaPLC1 overexpression vector was transferred to Arabidopsis and selected to T3 generation for drought and heat stress treatment.

RESULTS

After 4 h of drought and heat stress, the SOD activity, MDA and soluble sugar content of the two cultivars with inhibitor were higher than those without inhibitor, the chlorophyll content decreased. CS seedlings showed significant wilting phenomenon, and TAM107 showed slight wilting. After the elimination of drought and heat stress, all seedling wilting gradually recovered, while the leaf tips of the two varieties treated with inhibitors began to wilt and turn yellow, which was more significant 5 days after the drought and heat stress, while the degree of spring wilting and yellow in CS was earlier than that in TAM107. The expression patterns of TaPLC1 gene were different in the two cultivars, but the expression levels reached the maximum at 30 min of heat stress. The change of TaPLC1 expression in TAM107 without inhibitor treatment was significantly greater than that in CS. The expression level of TaPLC1 in the two cultivars under stress was significantly different between the two cultivars treated with inhibitor and untreated, and was lower than that of the normal plants under normal conditions. These results indicated that inhibition of TaPLC1 gene expression could enhance the sensitivity of seedlings to stress. In Arabidopsis, the root lengths of transgenic and wild-type seedlings were shortened after drought stress treatment, but the root lengths of transgenic plants decreased slightly. And the expression of TaPLC1 gene was significantly increased after drought and heat stress. This indicated that overexpression of TaPLC1 improved drought resistance of Arabidopsis.

CONCLUSIONS

The results of this study suggest that TaPLC1 may be involved in the regulation mechanism of drought and heat stress in wheat.

Jasmonic Acid Signaling and Molecular Crosstalk with Other Phytohormones

Plants continually monitor their innate developmental status and external environment and make adjustments to balance growth, differentiation and stress responses using a complex and highly interconnected regulatory network composed of various signaling molecules and regulatory proteins. Phytohormones are an essential group of signaling molecules that work through a variety of different pathways conferring plasticity to adapt to the everchanging developmental and environmental cues. Of these, jasmonic acid (JA), a lipid-derived molecule, plays an essential function in controlling many different plant developmental and stress responses. In the past decades, significant progress has been made in our understanding of the molecular mechanisms that underlie JA metabolism, perception, signal transduction and its crosstalk with other phytohormone signaling pathways. In this review, we discuss the JA signaling pathways starting from its biosynthesis to JA-responsive gene expression, highlighting recent advances made in defining the key transcription factors and transcriptional regulatory proteins involved. We also discuss the nature and degree of crosstalk between JA and other phytohormone signaling pathways, highlighting recent breakthroughs that broaden our knowledge of the molecular bases underlying JA-regulated processes during plant development and biotic stress responses.

Regulation of Sixth Seminal Root Formation by Jasmonate in Triticum aestivum L

A well-developed root system is an important characteristic of crop plants, which largely determines their productivity, especially under conditions of water and nutrients deficiency. Being Poaceous, wheat has more than one seminal root. The number of grown seminal roots varies in different wheat accessions and is regulated by environmental factors. Currently, the molecular mechanisms determining the number of germinated seminal roots remain poorly understood. The analysis of the root system development in germinating seeds of genetically modified hexaploid wheat plants with altered activity of jasmonate biosynthesis pathway and seeds exogenously treated with methyl jasmonate revealed the role of jasmonates in the regulation of sixth seminal root development. This regulatory effect strongly depends on the jasmonate concentration and the duration of the exposure to this hormone. The maximum stimulatory effect of exogenously applied methyl jasmonate on the formation of the sixth seminal root was achieved at 200 μM concentration after 48 h of treatment. Further increase in concentration and exposure time does not increase the stimulating effect. While 95% of non-transgenic plants under non-stress conditions possess five or fewer seminal roots, the number of plants with developed sixth seminal root reaches up to 100% when selected transgenic lines are treated with methyl jasmonate.

Diverse role of phytic acid in plants and approaches to develop low-phytate grains to enhance bioavailability of micronutrients

Natural or synthetic compounds that interfere with the bioavailability of nutrients are called antinutrients. Phytic acid (PA) is one of the major antinutrients present in the grains and acts as a chelator of micronutrients. The presence of six reactive phosphate groups in PA hinders the absorption of micronutrients in the gut of non-ruminants. Consumption of PA-rich diet leads to deficiency of minerals such as iron and zinc among human population. On the contrary, PA is a natural antioxidant, and PA-derived molecules function in various signal transduction pathways. Therefore, optimal concentration of PA needs to be maintained in plants to avoid adverse pleiotropic effects, as well as to ensure micronutrient bioavailability in the diets. Given this, the chapter enumerates the structure, biosynthesis, and accumulation of PA in food grains followed by their roles in growth, development, and stress responses. Further, the chapter elaborates on the antinutritional properties of PA and explains the conventional breeding and transgene-based approaches deployed to develop low-PA varieties. Studies have shown that conventional breeding methods could develop low-PA lines; however, the pleiotropic effects of these methods viz. reduced yield, embryo abnormalities, and poor seed quality hinder the use of breeding strategies. Overexpression of phytase in the endosperm and RNAi-mediated silencing of genes involved in myo-inositol biosynthesis overcome these constraints. Next-generation genome editing approaches, including CRISPR-Cas9 enable the manipulation of more than one gene involved in PA biosynthesis pathway through multiplex editing, and scope exists to deploy such tools in developing varieties with optimal PA levels.

Breaking Bad News: Dynamic Molecular Mechanisms of Wound Response in Plants

Recognition and repair of damaged tissue are an integral part of life. The failure of cells and tissues to appropriately respond to damage can lead to severe dysfunction and disease. Therefore, it is essential that we understand the molecular pathways of wound recognition and response. In this review, we aim to provide a broad overview of the molecular mechanisms underlying the fate of damaged cells and damage recognition in plants. Damaged cells release the so-called damage associated molecular patterns to warn the surrounding tissue. Local signaling through calcium (Ca2+), reactive oxygen species (ROS), and hormones, such as jasmonic acid, activates defense gene expression and local reinforcement of cell walls to seal off the wound and prevent evaporation and pathogen colonization. Depending on the severity of damage, Ca2+, ROS, and electrical signals can also spread throughout the plant to elicit a systemic defense response. Special emphasis is placed on the spatiotemporal dimension in order to obtain a mechanistic understanding of wound signaling in plants.

Quantitative Hormone Signaling Output Analyses of Arabidopsis thaliana Interactions With Virulent and Avirulent Hyaloperonospora arabidopsidis Isolates at Single-Cell Resolution

The phytohormones salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) are central regulators of biotic and abiotic stress responses in Arabidopsis thaliana. Here, we generated modular fluorescent protein-based reporter lines termed COLORFUL-PR1pro, -VSP2pro, and -PDF1.2apro. These feature hormone-controlled nucleus-targeted transcriptional output sensors and the simultaneous constitutive expression of spectrally separated nuclear reference and plasma membrane-localized reporters. This set-up allowed the study of cell-type specific hormone activities, cellular viability and microbial invasion. Moreover, we developed a software-supported high-throughput confocal microscopy imaging protocol for output quantification to resolve the spatio-temporal dynamics of respective hormonal signaling activities at single-cell resolution. Proof-of-principle analyses in A. thaliana leaves revealed distinguished hormone sensitivities in mesophyll, epidermal pavement and stomatal guard cells, suggesting cell type-specific regulatory protein activities. In plant-microbe interaction studies, we found that virulent and avirulent Hyaloperonospora arabidopsidis (Hpa) isolates exhibit different invasion dynamics and induce spatio-temporally distinct hormonal activity signatures. On the cellular level, these hormone-controlled reporter signatures demarcate the nascent sites of Hpa entry and progression, and highlight initiation, transduction and local containment of immune signals.

Methyljasmonate and salicylic acid contribute to the control of Tilletia controversa Kühn, causal agent of wheat dwarf bunt

Tilletia controversa Kühn (TCK) is the causal agent of dwarf bunt of wheat, a destructive disease in wheat-growing regions of the world. The role of Meja, SA and Meja + SA were characterized for their control of TCK into roots, coleoptiles and anthers. The response of the defence genes PR-10a, Catalase, COI1-1, COII-2 and HRin1 was upregulated by Meja, SA and Meja + SA treatments, but Meja induced high level of expression compared to SA and Meja + SA at 1, 2, and 3 weeks in roots and coleoptiles, respectively. The severity of TCK effects in roots was greater at 1 week, but it decreased at 2 weeks in all treatments. We also investigated TCK hyphae proliferation into coleoptiles at 3 weeks and into anthers to determine whether hyphae move from the roots to the upper parts of the plants. The results showed that no hyphae were present in the coleoptiles and anthers of Meja-, SA- and Meja + SA-treated plants, while the hyphae were located on epidermal and sub-epidermal cells of anthers. In addition, the severity of hyphae increased with the passage of time as anthers matured. Bunted seeds were observed in the non-treated inoculated plants, while no disease symptoms were observed in the resistance of inducer treatments and control plants. Plant height was reduced after TCK infection compared to that of the treated inoculated and non-inoculated treatments. Together, these results suggested that Meja and SA display a distinct role in activation of defence genes in the roots and coleoptiles and that they eliminate the fungal pathogen movement to upper parts of the plants with the passage of time as the anthers mature.

Jasmonic Acid at the Crossroads of Plant Immunity and Pseudomonas syringae Virulence

Sensing of pathogen infection by plants elicits early signals that are transduced to affect defense mechanisms, such as effective blockage of pathogen entry by regulation of stomatal closure, cuticle, or callose deposition, change in water potential, and resource acquisition among many others. Pathogens, on the other hand, interfere with plant physiology and protein functioning to counteract plant defense responses. In plants, hormonal homeostasis and signaling are tightly regulated; thus, the phytohormones are qualified as a major group of signaling molecules controlling the most widely tinkered regulatory networks of defense and counter-defense strategies. Notably, the phytohormone jasmonic acid mediates plant defense responses to a wide array of pathogens. In this review, we present the synopsis on the jasmonic acid metabolism and signaling, and the regulatory roles of this hormone in plant defense against the hemibiotrophic bacterial pathogen Pseudomonas syringae. We also elaborate on how this pathogen releases virulence factors and effectors to gain control over plant jasmonic acid signaling to effectively cause disease. The findings discussed in this review may lead to ideas for the development of crop cultivars with enhanced disease resistance by genetic manipulation.

Systemic induction of phosphatidylinositol-based signaling in leaves of arbuscular mycorrhizal rice plants

Most land plants form beneficial associations with arbuscular mycorrhizal (AM) fungi which improves mineral nutrition, mainly phosphorus, in the host plant in exchange for photosynthetically fixed carbon. Most of our knowledge on the AM symbiosis derives from dicotyledonous species. We show that inoculation with the AM fungus Funneliformis mosseae stimulates growth and increases Pi content in leaves of rice plants (O. sativa, cv Loto, ssp japonica). Although rice is a host for AM fungi, the systemic transcriptional responses to AM inoculation, and molecular mechanisms underlying AM symbiosis in rice remain largely elusive. Transcriptomic analysis identified genes systemically regulated in leaves of mycorrhizal rice plants, including genes with functions associated with the biosynthesis of phospholipids and non-phosphorus lipids (up-regulated and down-regulated, respectively). A coordinated regulation of genes involved in the biosynthesis of phospholipids and inositol polyphosphates, and genes involved in hormone biosynthesis and signaling (jasmonic acid, ethylene) occurs in leaves of mycorrhizal rice. Members of gene families playing a role in phosphate starvation responses and remobilization of Pi were down-regulated in leaves of mycorrhizal rice. These results demonstrated that the AM symbiosis is accompanied by systemic transcriptional responses, which are potentially important to maintain a stable symbiotic relationship in rice plants.

Current Utility of Plant Growth-Promoting Rhizobacteria as Biological Control Agents towards Plant-Parasitic Nematodes

Plant-parasitic nematodes (PPN) are among the most economically and ecologically damaging pests, causing severe losses of crop production worldwide. Chemical-based nematicides have been widely used, but these may have adverse effects on human health and the environment. Hence, biological control agents (BCAs) have become an alternative option for controlling PPN, since they are environmentally friendly and cost effective. Lately, a major effort has been made to evaluate the potential of a commercial grade strain of plant growth-promoting rhizobacteria (PGPR) as BCAs, because emerging evidence has shown that PGPR can reduce PPN in infested plants through direct and/or indirect antagonistic mechanisms. Direct antagonism occurs by predation, release of antinematicidal metabolites and semiochemicals, competition for nutrients, and niche exclusion. However, the results of direct antagonism may be inconsistent due to unknown endogenous and exogenous factors that may prevent PGPR from colonizing plant's roots. On the other hand, indirect antagonism may occur from the induced systemic resistance (ISR) that primes whole plants to better fight against various biotic and abiotic constraints, actuating faster and/or stronger defense responses (adaption), enhancing their promise as BCAs. Hence, this review will briefly revisit (i) two modes of PGPR in managing PPN, and (ii) the current working models and many benefits of ISR, in the aim of reassessing current progresses and future directions for isolating more effective BCAs and/or developing better PPN management strategy.

Signalling Pinpointed to the Tip: The Complex Regulatory Network That Allows Pollen Tube Growth

Plants display a complex life cycle, alternating between haploid and diploid generations. During fertilisation, the haploid sperm cells are delivered to the female gametophyte by pollen tubes, specialised structures elongating by tip growth, which is based on an equilibrium between cell wall-reinforcing processes and turgor-driven expansion. One important factor of this equilibrium is the rate of pectin secretion mediated and regulated by factors including the exocyst complex and small G proteins. Critically important are also non-proteinaceous molecules comprising protons, calcium ions, reactive oxygen species (ROS), and signalling lipids. Among the latter, phosphatidylinositol 4,5-bisphosphate and the kinases involved in its formation have been assigned important functions. The negatively charged headgroup of this lipid serves as an interaction point at the apical plasma membrane for partners such as the exocyst complex, thereby polarising the cell and its secretion processes. Another important signalling lipid is phosphatidic acid (PA), that can either be formed by the combination of phospholipases C and diacylglycerol kinases or by phospholipases D. It further fine-tunes pollen tube growth, for example by regulating ROS formation. How the individual signalling cues are intertwined or how external guidance cues are integrated to facilitate directional growth remain open questions.

Same same, but different: growth responses of primary and lateral roots

The root system architecture describes the shape and spatial arrangement of roots within the soil. Its spatial distribution depends on growth and branching rates as well as directional organ growth. The embryonic primary root gives rise to lateral (secondary) roots, and the ratio of both root types changes over the life span of a plant. Most studies have focused on the growth of primary roots and the development of lateral root primordia. Comparably less is known about the growth regulation of secondary root organs. Here, we review similarities and differences between primary and lateral root organ growth, and emphasize particularly how external stimuli and internal signals differentially integrate root system growth.

Molecular Rewiring of the Jasmonate Signaling Pathway to Control Auxin-Responsive Gene Expression

The plant hormone jasmonic acid (JA) has an important role in many aspects of plant defense response and developmental process. JA triggers interaction between the F-box protein COI1 and the transcriptional repressors of the JAZ family that leads the later to proteasomal degradation. The Jas-motif of JAZs is critical for mediating the COI1 and JAZs interaction in the presence of JA. Here, by using the protoplast transient gene expression system we reported that the Jas-motif of JAZ1 was necessary and sufficient to target a foreign reporter protein for COI1-facilitated degradation. We fused the Jas-motif to the SHY2 transcriptional repressor of auxin signaling pathway to create a chimeric protein JaSHY. Interestingly, JaSHY retained the transcriptional repressor function while become degradable by the JA coreceptor COI1 in a JA-dependent fashion. Moreover, the JA-induced and COI1-facilitated degradation of JaSHY led to activation of a synthetic auxin-responsive promoter activity. These results showed that the modular components of JA signal transduction pathway can be artificially redirected to regulate auxin signaling pathway and control auxin-responsive gene expression. Our work provides a general strategy for using synthetic biology approaches to explore and design cell signaling networks to generate new cellular functions in plant systems.

Integrated multi-omics framework of the plant response to jasmonic acid

Understanding the systems-level actions of transcriptional responses to hormones provides insight into how the genome is reprogrammed in response to environmental stimuli. Here, we investigated the signalling pathway of the hormone jasmonic acid (JA), which controls a plethora of critically important processes in plants and is orchestrated by the transcription factor MYC2 and its closest relatives in Arabidopsis thaliana. We generated an integrated framework of the response to JA, which spans from the activity of master and secondary regulatory transcription factors, through gene expression outputs and alternative splicing, to protein abundance changes, protein phosphorylation and chromatin remodelling. We integrated time-series transcriptome analysis with (phospho)proteomic data to reconstruct gene regulatory network models. These enabled us to predict previously unknown points of crosstalk of JA to other signalling pathways and to identify new components of the JA regulatory mechanism, which we validated through targeted mutant analysis. These results provide a comprehensive understanding of how a plant hormone remodels cellular functions and plant behaviour, the general principles of which provide a framework for analyses of cross-regulation between other hormone and stress signalling pathways.

Can Inositol Pyrophosphates Inform Strategies for Developing Low Phytate Crops?

Inositol pyrophosphates (PP-InsPs) are an emerging class of "high-energy" intracellular signaling molecules, containing one or two diphosphate groups attached to an inositol ring, that are connected with phosphate sensing, jasmonate signaling, and inositol hexakisphosphate (InsP6) storage in plants. While information regarding this new class of signaling molecules in plants is scarce, the enzymes responsible for their synthesis have recently been elucidated. This review focuses on InsP6 synthesis and its conversion into PP-InsPs, containing seven and eight phosphate groups (InsP7 and InsP8). These steps involve two types of enzymes: the ITPKs that phosphorylate InsP6 to InsP7, and the PPIP5Ks that phosphorylate InsP7 to InsP8. This review also considers the potential roles of PP-InsPs in plant hormone and inorganic phosphate (Pi) signaling, along with an emerging role in bioenergetic homeostasis. PP-InsP synthesis and signaling are important for plant breeders to consider when developing strategies that reduce InsP6 in plants, as this will likely also reduce PP-InsPs. Thus, this review is primarily intended to bridge the gap between the basic science aspects of PP-InsP synthesis/signaling and breeding/engineering strategies to fortify foods by reducing InsP6.

Jasmonic Acid Signaling Pathway in Response to Abiotic Stresses in Plants

Plants as immovable organisms sense the stressors in their environment and respond to them by means of dedicated stress response pathways. In response to stress, jasmonates (jasmonic acid, its precursors and derivatives), a class of polyunsaturated fatty acid-derived phytohormones, play crucial roles in several biotic and abiotic stresses. As the major immunity hormone, jasmonates participate in numerous signal transduction pathways, including those of gene networks, regulatory proteins, signaling intermediates, and proteins, enzymes, and molecules that act to protect cells from the toxic effects of abiotic stresses. As cellular hubs for integrating informational cues from the environment, jasmonates play significant roles in alleviating salt stress, drought stress, heavy metal toxicity, micronutrient toxicity, freezing stress, ozone stress, CO₂ stress, and light stress. Besides these, jasmonates are involved in several developmental and physiological processes throughout the plant life. In this review, we discuss the biosynthesis and signal transduction pathways of the JAs and the roles of these molecules in the plant responses to abiotic stresses.

Identity and functions of inorganic and inositol polyphosphates in plants

Inorganic polyphosphates (polyPs) and inositol pyrophosphates (PP-InsPs) form important stores of inorganic phosphate and can act as energy metabolites and signaling molecules. Here we review our current understanding of polyP and inositol phosphate (InsP) metabolism and physiology in plants. We outline methods for polyP and InsP detection, discuss the known plant enzymes involved in their synthesis and breakdown, and summarize the potential physiological and signaling functions for these enigmatic molecules in plants.

Reconstitution of the Jasmonate Signaling Pathway in Plant Protoplasts

The phytohormone jasmonic acid (JA) plays an important role in various plant developmental processes and environmental adaptations. The JA signaling pathway has been well-elucidated in the reference plant Arabidopsis thaliana. It starts with the perception of the active JA derivative, jasmonoyl-isoleucine (JA-Ile), by the F-box protein COI1 which is part of the E3-ligase SCF^COI1. Binding of JA-Ile enables the interaction between COI1 and JAZ repressor proteins. Subsequent degradation of JAZ proteins leads to the activation of transcription factors like e.g., MYC2. Here we demonstrate that the pathway can be reconstituted in transiently transformed protoplasts. Analysis of the stability of a JAZ1-fLuc fusion protein as a function of COI1 transiently expressed in coi1 protoplasts allows structure function analysis of both JAZs and COI1. Using this system, we found that conserved cysteines in COI1 influence steady state COI1 protein levels. Using a luciferase reporter gene under the control of the JAZ1 promoter enable to address those features of JAZ1 that are required for MYC2 repression. Interestingly, the conserved TIFY-motif previously described to interact with NINJA to recruit the corepressor TOPLESS is not necessary for repression. This result is in favor of the alternative repression mode that proposes a direct competition between repressive JAZs and promotive MEDIATOR25 at MYC2. Finally, using protoplasts from the aos coi1 double mutant, which is deficient in JA synthesis and perception, we provide a system that has the potential to study the activity of different COI1 variants in the presence of different ligands.

Intracellular phosphate homeostasis - A short way from metabolism to signaling

Phosphorus in plant cells occurs in inorganic form as both ortho- and pyrophosphate or bound to organic compounds, like e.g., nucleotides, phosphorylated metabolites, phospholipids, phosphorylated proteins, or phytate as P storage in the vacuoles of seeds. Individual compartments of the cell are surrounded by membranes that are selective barriers to avoid uncontrolled solute exchange. A controlled exchange of phosphate or phosphorylated metabolites is accomplished by specific phosphate transporters (PHTs) and the plastidial phosphate translocator family (PTs) of the inner envelope membrane. Plastids, in particular chloroplasts, are the site of various anabolic sequences of enzyme-catalyzed reactions. Apart from their role in metabolism PHTs and PTs are presumed to be also involved in communication between organelles and plant organs. Here we will focus on the integration of phosphate transport and homeostasis in signaling processes. Recent developments in this field will be critically assessed and potential future developments discussed. In particular, the occurrence of various plastid types in one organ (i.e. the leaf) with different functions with respect to metabolism or sensing, as has been documented recently following a tissue-specific proteomics approach (Beltran et al., 2018), will shed new light on functional aspects of phosphate homeostasis.

Two bifunctional inositol pyrophosphate kinases/phosphatases control plant phosphate homeostasis

Many eukaryotic proteins regulating phosphate (Pi) homeostasis contain SPX domains that are receptors for inositol pyrophosphates (PP-InsP), suggesting that PP-InsPs may regulate Pi homeostasis. Here we report that deletion of two diphosphoinositol pentakisphosphate kinases VIH1/2 impairs plant growth and leads to constitutive Pi starvation responses. Deletion of phosphate starvation response transcription factors partially rescues vih1 vih2 mutant phenotypes, placing diphosphoinositol pentakisphosphate kinases in plant Pi signal transduction cascades. VIH1/2 are bifunctional enzymes able to generate and break-down PP-InsPs. Mutations in the kinase active site lead to increased Pi levels and constitutive Pi starvation responses. ATP levels change significantly in different Pi growth conditions. ATP-Mg2+ concentrations shift the relative kinase and phosphatase activities of diphosphoinositol pentakisphosphate kinases in vitro. Pi inhibits the phosphatase activity of the enzyme. Thus, VIH1 and VIH2 relay changes in cellular ATP and Pi concentrations to changes in PP-InsP levels, allowing plants to maintain sufficient Pi levels.

Role for Arabidopsis PLC7 in Stomatal Movement, Seed Mucilage Attachment, and Leaf Serration

Phospholipase C (PLC) has been suggested to play important roles in plant stress and development. To increase our understanding of PLC signaling in plants, we have started to analyze knock-out (KO), knock-down (KD) and overexpression mutants of Arabidopsis thaliana, which contains nine PLCs. Earlier, we characterized PLC2, PLC3 and PLC5. Here, the role of PLC7 is functionally addressed. Promoter-GUS analyses revealed that PLC7 is specifically expressed in the phloem of roots, leaves and flowers, and is also present in trichomes and hydathodes. Two T-DNA insertion mutants were obtained, i.e., plc7-3 being a KO- and plc7-4 a KD line. In contrast to earlier characterized phloem-expressed PLC mutants, i.e., plc3 and plc5, no defects in primary- or lateral root development were found for plc7 mutants. Like plc3 mutants, they were less sensitive to ABA during stomatal closure. Double-knockout plc3 plc7 lines were lethal, but plc5 plc7 (plc5/7) double mutants were viable, and revealed several new phenotypes, not observed earlier in the single mutants. These include a defect in seed mucilage, enhanced leaf serration, and an increased tolerance to drought. Overexpression of PLC7 enhanced drought tolerance too, similar to what was earlier found for PLC3-and PLC5 overexpression. In vivo 32Pi-labeling of seedlings and treatment with sorbitol to mimic drought stress, revealed stronger PIP2 responses in both drought-tolerant plc5/7 and PLC7-OE mutants. Together, these results show novel functions for PLC in plant stress and development. Potential molecular mechanisms are discussed.

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

Background

COI (CORONATINE INSENSITIVE), an F-box component of the Skp1-Cullin-F-box protein (SCF^COI1) ubiquitin E3 ligase, plays important roles in the regulation of plant growth and development. Recent studies have shown that COIs are involved in pollen fertility. In this study, we identified and characterized COI genes in the wheat genome and analyzed expression patterns under abiotic stress.

Results

A total of 18 COI candidate sequences for 8 members of COI gene family were isolated in wheat (Triticum aestivum L.). Phylogenetic and structural analyses showed that these COI genes could be divided into seven distinct subfamilies. The COI genes showed high expression in stamens and glumes. The qRT-PCR results revealed that wheat COIs were involved in several abiotic stress responses and anther/glume dehiscence in the photoperiod-temperature sensitive genic male sterile (PTGMS) wheat line BS366.

Conclusions

The structural characteristics and expression patterns of the COI gene family in wheat as well as the stress-responsive and differential tissue-specific expression profiles of each TaCOI gene were examined in PTGMS wheat line BS366. In addition, we examined SA- and MeJA-induced gene expression in the wheat anther and glume to investigate the role of COI in the JA signaling pathway, involved in the regulation of abnormal anther dehiscence in the PTGMS wheat line. The results of this study contribute novel and detailed information about the TaCOI gene family in wheat and could be used as a benchmark for future studies of the molecular mechanisms of PTGMS in other crops.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5116-9) contains supplementary material, which is available to authorized users.

Knock-Down of Arabidopsis PLC5 Reduces Primary Root Growth and Secondary Root Formation While Overexpression Improves Drought Tolerance and Causes Stunted Root Hair Growth

Phospholipase C (PLC) is a well-known signaling enzyme in metazoans that hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) to produce inositol 1,4,5-trisphosphate and diacylglycerol as second messengers involved in mutiple processes. Plants contain PLC too, but relatively little is known about its function there. The model system Arabidopsis thaliana contains nine PLC genes. Reversed genetics have implicated several roles for PLCs in plant development and stress signaling. Here, PLC5 is functionally addressed. Promoter-β-glucuronidase (GUS) analyses revealed expression in roots, leaves and flowers, predominantly in vascular tissue, most probably phloem companion cells, but also in guard cells, trichomes and root apical meristem. Only one plc5-1 knock-down mutant was obtained, which developed normally but grew more slowly and exhibited reduced primary root growth and decreased lateral root numbers. These phenotypes could be complemented by expressing the wild-type gene behind its own promoter. Overexpression of PLC5 (PLC5-OE) using the UBQ10 promoter resulted in reduced primary and secondary root growth, stunted root hairs, decreased stomatal aperture and improved drought tolerance. PLC5-OE lines exhibited strongly reduced phosphatidylinositol 4-monophosphate (PIP) and PIP2 levels and increased amounts of phosphatidic acid, indicating enhanced PLC activity in vivo. Reduced PIP2 levels and stunted root hair growth of PLC5-OE seedlings could be recovered by inducible overexpression of a root hair-specific PIP 5-kinase, PIP5K3. Our results show that PLC5 is involved in primary and secondary root growth and that its overexpression improves drought tolerance. Independently, we provide new evidence that PIP2 is essential for the polar tip growth of root hairs.

Jasmonates: News on Occurrence, Biosynthesis, Metabolism and Action of an Ancient Group of Signaling Compounds

: Jasmonic acid (JA) and its related derivatives are ubiquitously occurring compounds of land plants acting in numerous stress responses and development. Recent studies on evolution of JA and other oxylipins indicated conserved biosynthesis. JA formation is initiated by oxygenation of α-linolenic acid (α-LeA, 18:3) or 16:3 fatty acid of chloroplast membranes leading to 12-oxo-phytodienoic acid (OPDA) as intermediate compound, but in Marchantiapolymorpha and Physcomitrellapatens, OPDA and some of its derivatives are final products active in a conserved signaling pathway. JA formation and its metabolic conversion take place in chloroplasts, peroxisomes and cytosol, respectively. Metabolites of JA are formed in 12 different pathways leading to active, inactive and partially active compounds. The isoleucine conjugate of JA (JA-Ile) is the ligand of the receptor component COI1 in vascular plants, whereas in the bryophyte M. polymorpha COI1 perceives an OPDA derivative indicating its functionally conserved activity. JA-induced gene expressions in the numerous biotic and abiotic stress responses and development are initiated in a well-studied complex regulation by homeostasis of transcription factors functioning as repressors and activators.

The Binding Mechanism Between Inositol Phosphate (InsP) and the Jasmonate Receptor Complex: A Computational Study

Jasmonates are critical plant hormones, mediating stress response in plants and regulating plant growth and development. The jasmonate receptor is a multi-component complex, composed of Arabidopsis SKP-LIKE PROTEIN1 (ASK1), CORONATINE INSENSITIVE 1 (COI1), inositol phosphate (InsP), and jasmonate ZIM-domain protein (JAZ). COI1 acts as multi-component signaling hub that binds with each component. InsP is suggested to play important roles in the hormone perception. How InsP binds with COI1 and the structural changes in COI1 upon binding with InsP, JA-Ile, and JAZ are not well understood. In this study, we integrated multiple computational methods, such as molecular docking, molecular dynamics simulations, residue interaction network analysis and binding free energy calculation, to explore the effect of InsP on the dynamic behavior of COI1 and the recognition mechanism of each component of the jasmonate receptor complex. We found that upon binding with InsP, JA-Ile, and JAZ1, the structure of COI1 becomes more compact. The binding of InsP with COI1 stabilizes the conformation of COI1 and promotes the binding between JA-Ile or JAZ1 and COI1. Analysis of the network parameters led to the identification of some hub nodes in this network, including Met88, His118, Arg120, Arg121, Arg346, Tyr382, Arg409, Trp467, and Lys492. The structural and dynamic details will be helpful for understanding the recognition mechanism of each component and the discovery and design of novel jasmonate signaling pathway modulators.

Modularity in Jasmonate Signaling for Multistress Resilience

The plant hormone jasmonate coordinates immune and growth responses to increase plant survival in unpredictable environments. The core jasmonate signaling pathway comprises several functional modules, including a repertoire of COI1-JAZ (CORONATINE INSENSITIVE1-JASMONATE-ZIM DOMAIN) coreceptors that couple jasmonoyl-l-isoleucine perception to the degradation of JAZ repressors, JAZ-interacting transcription factors that execute physiological responses, and multiple negative feedback loops to ensure timely termination of these responses. Here, we review the jasmonate signaling pathway with an emphasis on understanding how transcriptional responses are specific, tunable, and evolvable. We explore emerging evidence that JAZ proteins integrate multiple informational cues and mediate crosstalk by propagating changes in protein-protein interaction networks. We also discuss recent insights into the evolution of jasmonate signaling and highlight how plant-associated organisms manipulate the pathway to subvert host immunity. Finally, we consider how this mechanistic foundation can accelerate the rational design of jasmonate signaling for improving crop resilience and harnessing the wellspring of specialized plant metabolites.

Phytase overexpression in Arabidopsis improves plant growth under osmotic stress and in combination with phosphate deficiency

Engineering osmotolerant plants is a challenge for modern agriculture. An interaction between osmotic stress response and phosphate homeostasis has been reported in plants, but the identity of molecules involved in this interaction remains unknown. In this study we assessed the role of phytic acid (PA) in response to osmotic stress and/or phosphate deficiency in Arabidopsis thaliana. For this purpose, we used Arabidopsis lines (L7 and L9) expressing a bacterial beta-propeller phytase PHY-US417, and a mutant in inositol polyphosphate kinase 1 gene (ipk1-1), which were characterized by low PA content, 40% (L7 and L9) and 83% (ipk1-1) of the wild-type (WT) plants level. We show that the PHY-overexpressor lines have higher osmotolerance and lower sensitivity to abscisic acid than ipk1-1 and WT. Furthermore, PHY-overexpressors showed an increase by more than 50% in foliar ascorbic acid levels and antioxidant enzyme activities compared to ipk1-1 and WT plants. Finally, PHY-overexpressors are more tolerant to combined mannitol stresses and phosphate deficiency than WT plants. Overall, our results demonstrate that the modulation of PA improves plant growth under osmotic stress, likely via stimulation of enzymatic and non-enzymatic antioxidant systems, and that beside its regulatory role in phosphate homeostasis, PA may be also involved in fine tuning osmotic stress response in plants.

Plant ion channels and transporters in herbivory-induced signalling

In contrast to many biotic stresses that plants face, feeding by herbivores produces unique mechanical and chemical signatures. Plants have evolved effective systems to recognise these mechanical stimuli and chemical elicitors at the plasma membrane (PM), where this recognition generates ion fluxes, including an influx of Ca2+ that elicits cellular Ca2+ signalling, production of reactive oxygen species (ROS), and variation in transmembrane potential. These signalling events also function in propagation of long-distance signals (Ca2+ waves, ROS waves, and electrical signals), which contribute to rapid, systemic induction of defence responses. Recent studies have identified several candidate channels or transporters that likely produce these ion fluxes at the PM. Here, we describe the important roles of these channels/transporters in transduction or transmission of herbivory-induced early signalling events, long-distance signals, and jasmonic acid and green leaf volatile signalling in plants.

Control of plant phosphate homeostasis by inositol pyrophosphates and the SPX domain

Proteins containing a SPX domain are involved in phosphate (Pi) homeostasis, including Pi transport and adaptation to Pi deficiency. The SPX domain harbors a basic surface binding Pi at low affinity and inositol pyrophosphates (PP-InsPs) at high affinity. Genetic and biochemical studies revealed that PP-InsPs serve as ligands for the SPX domain. Residues in the PHO1 SPX domain involved in PP-InsPs binding are critical for its Pi export activity, and the interaction between SPX proteins and the PHR1 transcription factor, which results in PHR1 inactivation, is promoted by PP-InsPs. Changes in PP-InsPs levels in response to Pi deficiency may thus contribute to the adaptation of plants to stress via the modulation of the activity of SPX-containing proteins and their interactors. Modulating PP-InsP levels or the affinity/specificity of the SPX domain for PP-InsP could potentially be used to engineer crops to maintain high yield under reduced Pi fertilizer input.