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Authors: Sara Hailemariam, Chao-Jan Liao and Tesfaye Mengiste.
Trends in Plant Science (2024)
Highlights: Receptor-like cytoplasmic kinases (RLCKs) have become major players in plant immunity regardless of the pathways involved. RLCKs form regulatory nodes that link receptors to downstream regulators that modulate plant hormones, Ca2+ signaling, reactive oxygen species (ROS) accumulation as well as activation of mitogen-activated protein kinases (MAPKs), transcription regulators, and immune gene expression. Phosphorylation, ubiquitination, and other post-translational modifications by effectors regulate RLCKs, enabling functional versatility and homeostasis. As major integrators of signals from receptors, RLCKs are potential targets for biotechnological applications. RLCKs play pivotal roles in plant immunity by contributing to both PTI and ETI. Due to their critical functions, these kinases are targets for manipulation by pathogen effectors to attenuate PTI. RLCKs also directly or indirectly recognize effectors and activate ETI. The function of RLCKs in crop plant immunity is emerging.
Abstract: "The receptor-like kinase (RLK) family of receptors and the associated receptor-like cytoplasmic kinases (RLCKs) have expanded in plants because of selective pressure from environmental stress and evolving pathogens. RLCKs link pathogen perception to activation of coping mechanisms. RLK–RLCK modules regulate hormone synthesis and responses, reactive oxygen species (ROS) production, Ca2+ signaling, activation of mitogen-activated protein kinase (MAPK), and immune gene expression, all of which contribute to immunity. Some RLCKs integrate responses from multiple receptors recognizing distinct ligands. RLKs/RLCKs and nucleotide-binding domain, leucine-rich repeats (NLRs) were found to synergize, demonstrating the intertwined genetic network in plant immunity. Studies in arabidopsis (Arabidopsis thaliana) have provided paradigms about RLCK functions, but a lack of understanding of crop RLCKs undermines their application. In this review, we summarize current understanding of the diverse functions of RLCKs, based on model systems and observations in crop species, and the emerging role of RLCKs in pathogen and abiotic stress response signaling."
Author: Masatsugu Toyota.
Plant and Cell Physiology (2024)
Excerpts: "The precise nature of this rapid, long-range communication system remains incompletely understood in plants. However, events such as the propagation of increases in cytosolic Ca2+ concentration ([Ca2+]cyt), reactive oxygen species (ROS) and electrical signals spatiotemporally correlate with the systemic spread of wound responses (Farmer et al. 2020, Suda and Toyota 2022)."
"In this issue, Watanabe et al. (2024) simultaneously recorded changes in [Ca2+]cyt and surface potential in M. polymorpha and demonstrated a spatiotemporal coupling between long-range Ca2+ and electrical signals in response to mechanical injury and the underlying molecular machinery conserved in land plants."
"Mechanical wounding of thallus branch 1 caused an immediate increase in [Ca2+]cyt in the wounded region, and this [Ca2+]cyt change was transmitted within 1–2 min to distal unwounded branch 2 (Fig. 1). Interestingly, this Ca2+ wave did not extend beyond the intermediate site to branches 3 and 4, originating from distinct meristematic zones (Fig. 1)."
"In summary, Watanabe et al. (2024) experimentally demonstrated that the non-vascular liverwort Marchantia propagates Ca2+ and electrical signals in response to wounding, with velocities similar to those observed in vascular plants (i.e. 1–2 mm/s). Pharmacological and genetic analyses suggest that these signals were tightly coupled and required MpGLR but not MpTPC (Fig. 1), supporting the concept that GLR-mediated long-range signaling is widely conserved in land plants."
Authors: Yewei Zhou, Chunyan Wang, Yongqiang Yu, Zhaojun Ding and Tongda Xu.
The Innovation Life (2024)
Abstract: "Rapid auxin responses in plants are crucial in initiating cellular changes. These responses are involved in processes such as plasma membrane depolarization, cytoplasmic streaming, apoplastic pH changes, calcium influx, etc. Recent studies illustrated how auxin triggers rapid changes in protein phosphorylation in different species through both the ABP-TMK auxin perception at the cell surface and a conserved RAF-like kinase-based mechanism. These works uncovered an ancient system for rapid responses to the auxin signaling molecule, shedding light on its profound impact on various cellular pathways and functions."
Authors: Deepika Mittal, Janesh Kumar Gautam, Mahendra Varma, Amrutha Laie, Shruti Mishra, Smrutisanjita Behera and Jyothilakshmi Vadassery.
Plant, Cell & Environment (2024)
Abstract: "Jasmonic acid-isoleucine (JA-Ile) is a plant defence hormone whose cellular levels are elevated upon herbivory and regulate defence signalling. Despite their pivotal role, our understanding of the rapid cellular perception of bioactive JA-Ile is limited. This study identifies cell type-specific JA-Ile-induced Ca2+ signal and its role in self-amplification and plant elicitor peptide receptor (PEPR)-mediated signalling. Using the Ca2+ reporter, R-GECO1 in Arabidopsis, we have characterized a monophasic and sustained JA-Ile-dependent Ca2+ signature in leaf epidermal cells. The rapid Ca2+ signal is independent of positive feedback by the JA-Ile receptor, COI1 and the transporter, JAT1. Microarray analysis identified up-regulation of receptors, PEPR1 and PEPR2 upon JA-Ile treatment. The pepr1 pepr2 double mutant in R-GECO1 background exhibits impaired external JA-Ile induced Ca2+cyt elevation and impacts the canonical JA-Ile responsive genes. JA responsive transcription factor, MYC2 binds to the G-Box motif of PEPR1 and PEPR2 promoter and activates their expression upon JA-Ile treatment and in myc2 mutant, this is reduced. External JA-Ile amplifies AtPep-PEPR pathway by increasing the AtPep precursor, PROPEP expression. Our work shows a previously unknown non-canonical PEPR-JA-Ile-Ca2+-MYC2 signalling module through which plants sense JA-Ile rapidly to amplify both AtPep-PEPR and jasmonate signalling in undamaged cells."
Authors: Shouguang Huang, Like Shen, M. Rob G. Roelfsema, Dirk Becker and Rainer Hedrich.
Science (2023)
Editor's view: Protons (H+) and calcium ions (Ca2+) are often shuttled across cellular membranes and act as signals. In plants, protons accumulate highly in the extracellular space, whereas Ca2+ stores can be found in the endoplasmic reticulum and other cellular compartments. H+ and Ca2+ concentrations in the cytoplasm are often closely correlated during signaling events. Huang et al. introduced a light-gated protist-derived ion channel into plant cells, allowing selective transport of H+ but not Ca2+. They found that induction of H+ transport into the cytoplasm led to subsequent Ca2+ release. This work establishes a causal relationship between intracellular pH and Ca2+ signaling in guard cells and offers a new tool for manipulating ion movement in other contexts.
Abstract: "Although there has been long-standing recognition that stimuli-induced cytosolic pH alterations coincide with changes in calcium ion (Ca2+) levels, the interdependence between protons (H+) and Ca2+ remains poorly understood. We addressed this topic using the light-gated channelrhodopsin HcKCR2 from the pseudofungus Hyphochytrium catenoides, which operates as a H+ conductive, Ca2+ impermeable ion channel on the plasma membrane of plant cells. Light activation of HcKCR2 in Arabidopsis guard cells evokes a transient cytoplasmic acidification that sparks Ca2+ release from the endoplasmic reticulum. A H+-induced cytosolic Ca2+ signal results in membrane depolarization through the activation of Ca2+-dependent SLAC1/SLAH3 anion channels, which enabled us to remotely control stomatal movement. Our study suggests a H+-induced Ca2+ release mechanism in plant cells and establishes HcKCR2 as a tool to dissect the molecular basis of plant intracellular pH and Ca2+ signaling."
Authors: Ning Zhang, Songtao Gui and Yonghong Wang.
Molecular Plant (2023)
Excerpts: "Recently, two separate research groups have made noteworthy contributions to our understanding of gravity sensing in plants by investigating the role of amyloplast sedimentation in repolarizing LAZY/LZY proteins (Chen et al., 2023; Nishimura et al., 2023). Both studies observed the LAZY/LZY localization on the amyloplast and PM, and translocation of LAZY/LZY from statoliths to the PM in response to gravistimulation."
"Furthermore, Nishimura et al. (2023) discovered that AtLAZY/LZY polar localization can rapidly change upon gravistimulation, resulting in repolarization in the new gravity direction. More importantly, they also explicitly demonstrated the essential role of amyloplast sedimentation in achieving the polarization of AtLAZY/LZY on the PM by manipulating the amyloplasts with the optical tweezer. In this study, authors demonstrated AtLAZY/LZY polarity on the PM is established based on the amyloplast position, achieved through AtLAZY/LZY translocation from amyloplast to the PM."
"Chen et al. (2023) proposed a model for gravity perception in plant roots: Gravistimulation increases the phosphorylation of AtLAZY/LZY mediated by MAPK. This phosphorylation, in turn, strengthens the interaction between AtLAZY/LZY and TOCs on the surface of amyloplasts. Subsequently, amyloplast sedimentation takes AtLAZY/LZY to the new bottom of columella cells. Ultimately, AtLAZY/LZY translocates from amyloplasts to the adjacent PM, establishing a new polarity (Figure 1). These findings represent significant progress in our understanding of gravity sensing mechanisms in plants."
Authors: Yuri Aratani, Takuya Uemura, Takuma Hagihara, Kenji Matsui and Masatsugu Toyota.
Nature Communications (2023)
Editor's view: Plants sense volatiles emitted by injured neighboring plants and elicit defense responses to external threats. Here, the authors show that Arabidopsis leaves uptake two green leaf volatiles via stomata and trigger cytosolic Ca2+ defense signaling.
Abstract: "Plants perceive volatile organic compounds (VOCs) released by mechanically- or herbivore-damaged neighboring plants and induce various defense responses. Such interplant communication protects plants from environmental threats. However, the spatiotemporal dynamics of VOC sensory transduction in plants remain largely unknown. Using a wide-field real-time imaging method, we visualize an increase in cytosolic Ca2+ concentration ([Ca2+]cyt) in Arabidopsis leaves following exposure to VOCs emitted by injured plants. We identify two green leaf volatiles (GLVs), (Z)-3-hexenal (Z-3-HAL) and (E)-2-hexenal (E-2-HAL), which increase [Ca2+]cyt in Arabidopsis. These volatiles trigger the expression of biotic and abiotic stress-responsive genes in a Ca2+-dependent manner. Tissue-specific high-resolution Ca2+ imaging and stomatal mutant analysis reveal that [Ca2+]cyt increases instantly in guard cells and subsequently in mesophyll cells upon Z-3-HAL exposure. These results suggest that GLVs in the atmosphere are rapidly taken up by the inner tissues via stomata, leading to [Ca2+]cyt increases and subsequent defense responses in Arabidopsis leaves."
Authors: Tian Wang, Xuanyi Chen, Chuanfeng Ju and Cun Wang.
Plant Communications (2023)
Abstract: "Plant mineral nutrition is essential for both crop yields and human health. However, the uneven distribution of mineral elements over time and space leads to a lack or excess of available mineral elements in plants. Among the essential nutrients, Calcium (Ca2+) stands out as a prominent secondary messenger that plays crucial roles in response to extracellular stimuli in all eukaryotes. Distinct Ca2+ signatures with unique parameters are induced by different stresses and deciphered by various Ca2+ sensors. Recent advancements in research on the participation of Ca2+ signaling in the regulation of mineral elements has made great progress. In this review, we focus on the impact of Ca2+ signaling in plant mineral uptake and detoxification. Specifically, we emphasize the significance of Ca2+ signaling in regulating plant mineral nutrition and delve into key points and novel avenues for future investigations, aiming to offer new insights into plant ion homeostasis."
Authors: Shiv Mani Dubey, Soeun Han, Nathan Stutzman, Michael J. Prigge, Eva Medvecká, Matthieu Pierre Platre, Wolfgang Busch, Matyáš Fendrych and Mark Estelle.
Molecular Plant (2023)
Abstract: "The phytohormone auxin triggers root growth inhibition within seconds via a non-transcriptional pathway. Among members of the TIR1/AFBs auxin receptor family, AFB1 has a primary role in this rapid response. However, the unique features that confer this specific function have not been identified. Here we show that the N-terminal region of AFB1, including the F-box domain and residues that contribute to auxin binding, are essential and sufficient for its specific role in the rapid response. Substitution of the N-terminal region of AFB1 with that of TIR1 disrupts its distinct cytoplasm-enriched localization and activity in rapid root growth inhibition. Importantly, the N-terminal region of AFB1 is indispensable for auxin-triggered calcium influx which is a prerequisite for rapid root growth inhibition. Furthermore, AFB1 negatively regulates lateral root formation and transcription of auxin-induced genes, suggesting that it plays an inhibitory role in canonical auxin signaling. These results suggest that AFB1 may buffer the transcriptional auxin response while it regulates rapid changes in cell growth that contribute to root gravitropism."
Authors: Qingwen Wang, Tao Shen, Lan Ni, Chao Chen, Jingjing Jiang, Zhenzhen Cui, Shuang Wang, Fengjuan Xu, Runjiao Yan and Mingyi Jiang.
Molecular Plant (2023)
Abstract: "In rice, the Ca2+/calmodulin-dependent protein kinase OsDMI3 is an important positive regulator of abscisic acid (ABA) signaling. In ABA signaling, H2O2 is required for ABA-induced activation of OsDMI3, which in turn increase H2O2 production. However, how OsDMI3 regulates H2O2 production in ABA signaling remains unknown. Here we show that OsRbohB is the main NADPH oxidase involved in ABA-induced H2O2 production and ABA-mediated physiological responses. OsDMI3 directly interacts with and phosphorylates OsRbohB at Ser-191, which is OsDMI3-mediated site-specific phosphorylation in ABA signaling. Further analyses revealed that OsDMI3-mediated OsRbohB Ser-191 phosphorylation positively regulates the activity of NADPH oxidase and the production of H2O2 in ABA signaling, thereby enhancing the sensitivity of seed germination and root growth to ABA and plant tolerance to water stress and oxidative stress. Moreover, we discovered that the OsDMI3-mediated OsRbohB phosphorylation and H2O2 production is dependent on the sucrose non-fermenting 1-related protein kinases SAPK8/9/10, which phosphorylate OsRbohB at Ser-140 in ABA signaling. Taken together, these results not only reveal an important regulatory mechanism that directly activates Rboh for ABA-induced H2O2 production but also uncover the importance of this regulatory mechanism in ABA signaling."
Authors: Shiv Mani Dubey, Soeun Han, Nathan Stutzman, Michael J Prigge, Eva Medvecka, Matthieu Pierre Platre, Wolfgang Busch, Matyas Fendrych and Mark Estelle.
bioRxiv (2023)
Abstract: "The phytohormone auxin triggers root growth inhibition within seconds via a non-transcriptional pathway. Among members of the TIR1/AFBs auxin receptor family, AFB1 has a primary role in this rapid response. However, the unique features that confer this specific function have not been identified. Here we show that the N-terminal region of AFB1, including the F-box domain and residues that contribute to auxin binding, are essential and sufficient for its specific role in the rapid response. Substitution of the N-terminal region of AFB1 with that of TIR1 disrupts its distinct cytoplasm-enriched localization and activity in rapid root growth inhibition. Importantly, the N-terminal region of AFB1 is indispensable for auxin-triggered calcium influx which is a prerequisite for rapid root growth inhibition. Furthermore, AFB1 negatively regulates lateral root formation and transcription of auxin-induced genes, suggesting that it plays an inhibitory role in canonical auxin signaling. These results suggest that AFB1 may buffer the transcriptional auxin response while it regulates rapid changes in cell growth that contribute to root gravitropism."
Authors: Nelson B.C. Serre, Daša Wernerová, Pruthvi Vittal, Shiv Mani Dubey, Eva Medvecká, Adriana Jelínková, Jan Petrášek, Guido Grossmann and Matyáš Fendrych.
bioRxiv (2022)
Abstract: "Plant roots navigate in the dark soil environments following the gravity vector. Cell divisions in the meristem and rapid cell growth in the elongation zone propel the root tips through the soil. Actively elongating cells acidify their apoplast to enable cell wall extension by the activity of plasma membrane AHA H+-ATPases. The phytohormone auxin, central regulator of gravitropic response and root development, inhibits root cell growth, likely by rising the pH of the apoplast. However, the role of auxin in the regulation of the apoplastic pH gradient along the root tip is unclear. Here we show, by using an improved method for visualization and quantification of root surface pH, that the Arabidopsis thaliana root surface pH shows distinct acidic and alkaline zones, which are not primarily determined by the activity of AHA H+-ATPases. Instead, the distinct domain of alkaline pH in the root transition zone is controlled by a rapid auxin response module, consisting of the AUX1 auxin influx carrier, the AFB1 auxin co-receptor and the CNCG14 calcium channel. We demonstrate that the rapid auxin response pathway is required for an efficient navigation of the root tip."
Authors: Dali Fu, Zhenqian Zhang, Lukas Wallrad, Zhangqing Wang, Stefanie Höller, ChuanFeng Ju, Ina Schmitz-Thom, Panpan Huang, Lei Wang, Edgar Peiter, Jörg Kudla and Cun Wang.
PNAS (2022)
Significance: Manganese (Mn) deficiency represents a serious and widespread disturbance of crop nutrition in alkaline and calcareous soils. However, it has remained largely unknown how fluctuations in Mn supply are sensed and signaled and how the activity of Mn transporters is regulated. Here we discovered that Mn depletion triggers spatiotemporally defined multicellular Ca2+ oscillations in a specific “low Mn-sensing niche” in Arabidopsis roots. We identified the Ca2+ signal-decoding kinases CPK21 and CPK23 as regulating the Mn uptake transporter NRAMP1. We defined Thr498 in NRAMP1 as a target of both kinases and as a pivot mechanistically determining NRAMP1 activity. These findings delineate a Ca2+-CPK21/23-NRAMP1 axis as key mechanism for establishing plant resilience to limited Mn supply.
Abstract: "Homeostasis of the essential micronutrient manganese (Mn) is crucially determined through availability and uptake efficiency in all organisms. Mn deficiency of plants especially occurs in alkaline and calcareous soils, seriously restricting crop yield. However, the mechanisms underlying the sensing and signaling of Mn availability and conferring regulation of Mn uptake await elucidation. Here, we uncover that Mn depletion triggers spatiotemporally defined long-lasting Ca2+ oscillations in Arabidopsis roots. These Ca2+ signals initiate in individual cells, expand, and intensify intercellularly to transform into higher-order multicellular oscillations. Furthermore, through an interaction screen we identified the Ca2+-dependent protein kinases CPK21 and CPK23 as Ca2+ signal-decoding components that bring about translation of these signals into regulation of uptake activity of the high-affinity Mn transporter natural resistance associated macrophage proteins 1 (NRAMP1). Accordingly, a cpk21/23 double mutant displays impaired growth and root development under Mn-limiting conditions, while kinase overexpression confers enhanced tolerance to low Mn supply to plants. In addition, we define Thr498 phosphorylation within NRAMP1 as a pivot mechanistically determining NRAMP1 activity, as revealed by biochemical assays and complementation of yeast Mn uptake and Arabidopsis nramp1 mutants. Collectively, these findings delineate the Ca2+-CPK21/23-NRAMP1 axis as key for mounting plant Mn homeostasis."
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Authors: Zengkang Zhai, Qianqian Ao, Liuqing Yang, Fangxiao Lu, Haokun Cheng, Qinxin Fang, Chun Li, Qinqin Chen, Jingli Yan, Yongsheng Wei, Yuan-Qing Jiang and Bo Yang.
Journal of Food and Agricultural Chemistry (2024)
Abstract: "Global water deficit is a severe abiotic stress threatening the yielding and quality of crops. Abscisic acid (ABA) is a phytohormone that mediates drought tolerance. Protein kinases and phosphatases function as molecular switches in eukaryotes. Protein phosphatases type 2C (PP2Cs) are a major family that play essential roles in ABA signaling and stress responses. However, the role and underlying mechanism of PP2C in rapeseed (Brassica napus L.) mediating drought response has not been reported yet. Here, we characterized a PP2C family member, BnaPP2C37, and its expression level was highly induced by ABA and dehydration treatments. It negatively regulates drought tolerance in rapeseed. We further identified that BnaPP2C37 interacted with multiple PYR/PYL receptors and a drought regulator BnaCPK5 (calcium-dependent protein kinase 5) through yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. Specifically, BnaPYL1 and BnaPYL9 repress BnaPP2C37 phosphatase activity. Moreover, the pull-down assay and phosphatase assays show BnaPP2C37 interacts with BnaCPK5 to dephosphorylate BnaCPK5 and its downstream BnaABF3. Furthermore, a dual-luciferase assay revealed BnaPP2C37 transcript level was enhanced by BnaABF3 and BnaABF4, forming a negative feedback regulation to ABA response. In summary, we identified that BnaPP2C37 functions negatively in drought tolerance of rapeseed, and its phosphatase activity is repressed by BnaPYL1/9 whereas its transcriptional level is upregulated by BnaABF3/4."
Authors: Kenshiro Watanabe, Kenji Hashimoto, Kota Hasegawa, Hiroki Shindo, Yushin Tsuruda, Kamila Kupisz, Mateusz Koselski, Piotr Wasko, Kazimierz Trebacz and Kazuyuki Kuchitsu.
Plant and Cell Physiology (2024)
Abstract: "In response to both biotic and abiotic stresses, vascular plants transmit long-distance Ca2+ and electrical signals from localized stress sites to distant tissues through their vasculature. Various models have been proposed for the mechanisms underlying the long-distance signaling, primarily centered around the presence of vascular bundles. We here demonstrate that the non-vascular liverwort Marchantia polymorpha possesses a mechanism for propagating Ca2+ waves and electrical signals in response to wounding. The propagation velocity of these signals was approximately 1–2 mm s-1, equivalent to that observed in vascular plants. Both Ca2+ waves and electrical signals were inhibited by La3+ as well as tetraethylammonium chloride, suggesting the crucial importance of both Ca2+ channel(s) and K+ channel(s) in wound-induced membrane depolarization as well as the subsequent long-distance signal propagation. Simultaneous recordings of Ca2+ and electrical signals indicated a tight coupling between the dynamics of these two signaling modalities. Furthermore, molecular genetic studies revealed that a GLUTAMATE RECEPTOR-LIKE (GLR) channel plays a central role in the propagation of both Ca2+ waves and electrical signals. Conversely, none of the three two-pore channels were implicated in either signal propagation. These findings shed light on the evolutionary conservation of rapid long-distance Ca2+ wave and electrical signal propagation involving GLRs in land plants, even in the absence of vascular tissue."
Authors: Yanliang Guo and Hao Li.
In Book. "Melatonin in Plants: Role in Plant Growth, Development, and Stress Response" (2024). Editors: Anket Sharma and Golam Jalal Ahammed.
Abstract: "Numerous studies have proven evidence that melatonin plays an important regulatory role in plant growth, development, and defense against various biotic and abiotic stresses. As well as melatonin, plant hormones and many second messengers, such as calcium (Ca2+), reactive oxygen species (ROS), nitric oxide (NO), and hydrogen sulfide (H2S), also play important roles in the regulation of various physiological processes in plants. In recent years, increasing studies have indicated that melatonin interacts with plant hormones and many second messengers to regulate multiple physiological processes. The role of melatonin in regulating seed germination involves abscisic acid (ABA), gibberellins (GA), Ca2+ signal, and H2O2; in regulating stomatal movement involves ABA, Ca2+, ROS, and H2S; in regulating rhizogenesis involves auxin, ROS, and NO; in regulating fruit ripening involves ethylene (ETH), ROS, and NO; in regulating plant senescence involves ABA, cytokinins (CKs), Ca2+, ROS, and NO; in regulating tolerance to abiotic stress involves CK, ABA, ETH, jasmonic acid (JA), and all secondary signals mentioned above; in regulating disease resistance involves ETH, JA, salicylic acid (SA), ROS, and NO. Plant hormones and the second messengers also interact with each other, forming complex regulatory networks, to regulate multiple physiological processes in plants."
Authors: Hayet Houmani and Francisco J. Corpas.
Plant Physiology and Biochemistry (2024)
Highlights • Mineral nutrients are determinant factors for plant growth and development. • Some minerals have signaling properties and can mediate a stress response. • Nutrients such as Ca2+, K+, N, or Fe interact with other signaling molecules (hormones, NO, H2O2 or H2S) to exert their signaling function.
Abstract: "Plant cells are in constant communication to coordinate development processes and environmental reactions. Under stressful conditions, such communication allows the plant cells to adjust their activities and development. This is due to intercellular signaling events which involve several components. In plant development, cell-to-cell signaling is ensured by mobile signals hormones, hydrogen peroxide (H2O2), nitric oxide (NO), or hydrogen sulfide (H2S), as well as several transcription factors and small RNAs. Mineral nutrients, including macro and microelements, are determinant factors for plant growth and development and are, currently, recognized as potential signal molecules. This review aims to highlight the role of nutrients, particularly calcium, potassium, magnesium, nitrogen, phosphorus, and iron as signaling components with special attention to the mechanism of response against stress conditions."
Authors: Linlin Qi, Mateusz Kwiatkowski, Ivan Kulich, Huihuang Chen, Yongqiang Gao, Ping Yun, Lanxin Li, Sergey Shabala, Edward E. Farmer, Krzysztof Jaworski and Jiří Friml.
bioRxiv (2023)
Abstract: "The major developmental signal in plants, auxin is perceived by TIR1/AFB receptors. It triggers transcriptional reprogramming via well-established canonical mechanism but also elusive rapid, non-transcriptional responses. Here we demonstrate that TIR1/AFB receptors have, next to recently identified adenylate cyclase, also guanylate cyclase activity. Auxin perception activates independently the cAMP and cGMP production by TIR1/AFBs in vitro and increases cAMP and cGMP levels in planta with a slow and fast dynamics, respectively. Exogenous cGMP but not cAMP application induces rapid cytosolic Ca2+ transients and root growth inhibition, suggesting that TIR1/AFB-derived cGMP mediates rapid auxin responses. This unprecedented combination of adenylate and guanylate cyclase activities in a hormone receptor provides a new paradigm for how a single perception mechanism can mediate a multitude of diverse downstream responses."
In: phys.org
"Plants emit volatile organic compounds (VOCs) into the atmosphere upon mechanical damages or insect attacks. Undamaged neighboring plants sense the released VOCs as danger cues to activate defense responses against upcoming threats."
Authors: Chrysoula K. Pantazopoulou, Sara Buti, Chi Tam Nguyen, Lisa Oskam, Daan A. Weits, Edward E. Farmer, Kaisa Kajala and Ronald Pierik
Nature Communications (2023)
Editor's view: Pantazopoulou et al. discovered that leaves sense neighbors by mutual touching of hairs on their surface, called trichomes. Using fluorescent biosensors, they show that this triggers a calcium wave to activate leaf movement away from competitors
Abstract: "Plants detect their neighbors via various cues, including reflected light and touching of leaf tips, which elicit upward leaf movement (hyponasty). It is currently unknown how touch is sensed and how the signal is transferred from the leaf tip to the petiole base that drives hyponasty. Here, we show that touch-induced hyponasty involves a signal transduction pathway that is distinct from light-mediated hyponasty. We found that mechanostimulation of the leaf tip upon touching causes cytosolic calcium ([Ca2+]cyt induction in leaf tip trichomes that spreads towards the petiole. Both perturbation of the calcium response and the absence of trichomes reduce touch-induced hyponasty. Finally, using plant competition assays, we show that touch-induced hyponasty is adaptive in dense stands of Arabidopsis. We thus establish a novel, adaptive mechanism regulating hyponastic leaf movement in response to mechanostimulation by neighbors in dense vegetation."
Authors: Faiza Shafique Khan, Farhan Goher, Michael N. Paulsmeyer, Chun-Gen Hu and Jin-Zhi Zhang.
Plant Biology (2023)
Abstract: "Plants evolve stress-specific responses that sense changes in their external environmental conditions and develop various mechanisms for acclimatization and survival. Calcium (Ca2+) is an essential stress-sensing secondary messenger in plants. Ca2+ sensors, including calcium-dependent protein kinases (CDPKs), calmodulins (CaMs), CaM-like proteins (CMLs), and calcineurin B-like proteins (CBLs), are involved in jasmonates (JAs) signaling and biosynthesis. Moreover, JAs are phospholipid-derived phytohormones that control plant response to abiotic stresses. The JAs signaling pathway affects hormone-receptor gene transcription by binding to the basic helix-loop-helix (bHLH) transcription factor. MYC2 acts as a master regulator of JAs signaling module assimilated through genes. Ca2+ sensor CML regulates MYC2 and is involved in a distinct mechanism mediating JAs signaling during abiotic stresses. This review highlights the pivotal role of the Ca2+ sensors in JAs biosynthesis and MYC2-mediated JAs signaling during abiotic stresses in plants."
Authors: Miguel-Ángel Torres and Diego José Berlanga.
Molecular Plant (2023)
Excerpt: "In the accompanying article, Wang et al. (2023) identify in rice a new kinase that activates RBOH-dependent ROS production in ABA signaling. Rice Ca2+/CALMODULIN-DEPENDENT PROTEIN KINASE (CCaMK) DOESN'T MAKE INFECTIONS 3 (DMI3) was previously recognized as a positive regulator of ABA signaling, increasing ABA sensitivity and stress tolerance, and promoting the induction of antioxidant defences (Ni et al., 2019). In the present study, Wang et al. (2023) identify OsRBOHB as the main NADPH oxidase involved in ABA induced H2O2 production, and show that OsDMI3 interacts with and phosphorylates OsRBOHB at Ser-191. This phosphorylation positively regulates and enhances the production of H2O2 in ABA signaling, thereby increasing the sensitivity of seed germination and root growth to ABA and the tolerance of rice plants to drought and oxidative stress. The discovery of this novel regulatory mechanism of RBOH-dependent ROS production linked to Ca2+ signaling, added to the recent identification of proteins functioning as H2O2 sensors, point to the existence of positive feed-back regulatory loops to amplify H2O2 signaling and enhance downstream responses (Figure 1)."
Text of Figure: "Several amplification loops enhance H2O2 production and Ca2+ signaling in response to ABA. In the presence of ABA, loss of inhibition by class A PP2Cs activates SnRK2s (like OsSAPK8/9/10) that phosphorylate different targets, including RBOHs (Ser-140 in OsRBOHB) to trigger initial apoplastic H2O2 production. Downstream H2O2 targets comprise receptor kinases (like AtHPCA1) that activate channels allowing Ca+2 entry into the cytosol. Ca+2 will directly stimulate RBOH activity via its EF hands or indirectly through the activation of CCaMK (OsDMI3) that phosphorylates Ser-191 in OsRBOHB and further enhance RBOH activity to produce a second and sustained ABA-induced H2O2 burst. H2O2 can also contribute to enhance RBOH activity by oxidizing cysteins in clue inhibitors of ABA signaling, thus conforming additional amplification loops. H2O2 entering the cell through aquaporins (AQP) can oxidize clade K PP2Cs (OsPP45), releasing the inhibition of OsDMI3. In addition, H2O2 can oxidize thiol peroxidase PRXIIB, which forms a disulfide bridge with and inhibits clade A PP2Cs (AtABI2). Inhibition of these phosphatases allows further activation of SnRK2s to enhance downstream signaling, including phosphorylation of RBOH at Ser-140. These various positive feedback loops will augment H2O2 (and Ca+2) signaling to enhance ABA responses. Crosses indicate loss of inhibition of signaling components by ABA (blue) or H2O2 (red) that amplify signaling."
Authors: Huihuang Chen, Lanxin Li, Linlin Qi and Jiri Friml.
bioRxiv (2023)
Abstract: "Auxin is the major plant hormone regulating growth and development (Friml, 2022). Forward genetic approaches in the model plant Arabidopsis thaliana have identified major components of auxin signalling and established the canonical mechanism mediating transcriptional and thus developmental reprogramming. In this textbook view, TRANSPORT INHIBITOR RESPONSE 1 (TIR1)/AUXIN-SIGNALING F-BOX (AFBs) are auxin receptors, which act as F-box subunits determining the substrate specificity of the Skp1-Cullin1-F box protein (SCF) type E3 ubiquitin ligase complex. Auxin acts as a molecular glue increasing the affinity between TIR1/AFBs and the Aux/IAA repressors. Subsequently, Aux/IAAs are ubiquitinated and degraded, thus releasing auxin transcription factors from their repression making them free to mediate transcription of auxin response genes (Yu et al., 2022). Nonetheless, accumulating evidence suggests existence of rapid, non-transcriptional responses downstream of TIR1/AFBs such as auxin-induced cytosolic calcium (Ca2+) transients, plasma membrane depolarization and apoplast alkalinisation, all converging on the process of root growth inhibition and root gravitropism (Li et al., 2022). Particularly, these rapid responses are mostly contributed by predominantly cytosolic AFB1, while the long-term growth responses are mediated by mainly nuclear TIR1 and AFB2-5 (Li et al., 2021; Prigge et al., 2020; Serre et al., 2021). How AFB1 conducts auxin-triggered rapid responses and how it is different from TIR1 and AFB2-5 remains elusive. Here, we compare the roles of TIR1 and AFB1 in transcriptional and rapid response by modulating their subcellular localization and testing their ability to mediate transcriptional responses in yeast."
Authors: Anshika Tyagi, Sajad Ali, Goriparthi Ramakrishna, Anupam Singh, Suvin Park, Henda Mahmoudi and Hanhong Bae.
Journal of Plant Growth Regulation (2023)
Abstract: "Phytohormone-like plant growth regulators are becoming hallmarks in plant stress biology since they can offer incredible benefits to plants, such as increased crop output, improved growth features and stress tolerance. Among them polyamines (PAs) such as putrescine (Put), spermidine (Spd), and spermine (Spm), are recognized as important bio-stimulants that can boost plant growth, productivity, and stress tolerance, whether provided exogenously or synthesized endogenously by genetically engineered plants. However, the precise mechanism by which they regulate plant development and stress responses and their interactions with other signaling molecules remains unknown. Hence, unravelling the molecular complexity of PAs signaling in plants can help us to improve crop stress resistance and yield. This review focuses on the distribution, biosynthesis, and role of PAs in plant growth and development, abiotic stress tolerance, and the involvement of a possible novel interlinked signaling cascade between them. Further, we focused on our current understanding and knowledge gaps of how PAs interact with other signaling molecules like hormones and nitric oxide (NO) to regulate plant growth and stress tolerance in a coordinated manner. We also provide an overview of PA signaling in plants, focusing on calcium (Ca2+) and reactive oxygen species (ROS) under abiotic stress, and some key insights into omics and nanotechnology approach for future research."
Authors: Andras Bittner, Agata Cieśla, Kristina Gruden, Tjaša Lukan, Sakil Mahmud, Markus Teige, Ute C. Vothknecht and Bernhard Wurzinger.
Journal of Experimental Botany (2022)
Abstract: "Phytohormones are major signaling components that contribute to nearly all aspects of plant life. They constitute an interconnected communication network to fine-tune growth and development in response to the ever-changing environment. To this end, they have to coordinate with other signaling components, such as reactive oxygen species and calcium signals. On the one hand, the two endosymbiotic organelles, plastids and mitochondria, control various aspects of phytohormone signaling and harbor important steps of hormone precursor biosynthesis. On the other hand, phytohormones have feedback actions on organellar functions. In addition, organelles and phytohormones often act in parallel in a coordinated matter to regulate cellular functions. Therefore, linking organelle functions with increasing knowledge of phytohormone biosynthesis, perception, and signaling will reveal new aspects of plant stress tolerance. In this review, we highlight recent work on organelle–phytohormone interactions focusing on the major stress-related hormones abscisic acid, jasmonates, salicylic acid, and ethylene."
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