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1. The fast and the furious: rapid long-range signaling in plants

   https://doi.org/10.1093/plphys/kiaa098  

   Johns, Sarah ; Hagihara, Takuma ; Toyota, Masatsugu ; Gilroy, Simon ( January 2021 , Plant Physiology)

   null (Ed.)

   Plants possess a systemic signaling system whereby local stimuli can lead to rapid, plant-wide responses. In addition to the redistribution of chemical messengers that range from RNAs and peptides to hormones and metabolites, a communication system acting through the transmission of electrical, Ca2+, reactive oxygen species and potentially even hydraulic signals has also been discovered. This latter system can propagate signals across many cells each second and researchers are now beginning to uncover the molecular machineries behind this rapid communications network. Thus, elements such as the reactive oxygen species producing NAPDH oxidases and ion channels of the two pore channel, glutamate receptor-like and cyclic nucleotide gated families are all required for the rapid propagation of these signals. Upon arrival at their distant targets, these changes trigger responses ranging from the production of hormones, to changes in the levels of primary metabolites and shifts in patterns of gene expression. These systemic responses occur within seconds to minutes of perception of the initial, local signal, allowing for the rapid deployment of plant-wide responses. For example, an insect starting to chew on just a single leaf triggers preemptive antiherbivore defenses throughout the plant well before it has a chance to move on to the next leaf on its menu. 

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2. Ethylene-independent signaling by the ethylene precursor ACC in Arabidopsis ovular pollen tube attraction

   https://doi.org/10.1038/s41467-020-17819-9  

   Mou, Wangshu ; Kao, Yun-Ting ; Michard, Erwan ; Simon, Alexander A. ; Li, Dongdong ; Wudick, Michael M. ; Lizzio, Michael A. ; Feijó, José A. ; Chang, Caren ( August 2020 , Nature Communications)

   The phytohormone ethylene has numerous effects on plant growth and development. Its immediate precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), is a non-proteinogenic amino acid produced by ACC SYNTHASE (ACS). ACC is often used to induce ethylene responses. Here, we demonstrate that ACC exhibits ethylene-independent signaling inArabidopsis thalianareproduction. By analyzing anacsoctuple mutant with reduced seed set, we find that ACC signaling in ovular sporophytic tissue is involved in pollen tube attraction, and promotes secretion of the pollen tube chemoattractant LURE1.2. ACC activates Ca²⁺-containing ion currents via GLUTAMATE RECEPTOR-LIKE (GLR) channels in root protoplasts. In COS-7 cells expressing mossPpGLR1, ACC induces the highest cytosolic Ca²⁺elevation compared to all twenty proteinogenic amino acids. In ovules, ACC stimulates transient Ca²⁺elevation, and Ca²⁺influx in octuple mutant ovules rescues LURE1.2 secretion. These findings uncover a novel ACC function and provide insights for unraveling new physiological implications of ACC in plants.

    

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3. Orchestrating rapid long‐distance signaling in plants with Ca 2+ , ROS and electrical signals

   https://doi.org/10.1111/tpj.13492  

   Choi, Won‐Gyu ; Miller, Gad ; Wallace, Ian ; Harper, Jeffrey ; Mittler, Ron ; Gilroy, Simon ( March 2017 , The Plant Journal)

   Plants show a rapid systemic response to a wide range of environmental stresses, where the signals from the site of stimulus perception are transmitted to distal organs to elicit plant‐wide responses. A wide range of signaling molecules are trafficked through the plant, but a trio of potentially interacting messengers, reactive oxygen species (ROS), Ca²⁺and electrical signaling (‘trio signaling’) appear to form a network supporting rapid signal transmission. The molecular components underlying this rapid communication are beginning to be identified, such as theROSproducingNAPDHoxidaseRBOHD, the ion channel two pore channel 1 (TPC1), and glutamate receptor‐like channelsGLR3.3 andGLR3.6. The plant cell wall presents a plant‐specific route for possible propagation of signals from cell to cell. However, the degree to which the cell wall limits information exchange between cells via transfer of small molecules through an extracellular route, or whether it provides an environment to facilitate transmission of regulators such asROSor H⁺remains to be determined. Similarly, the role of plasmodesmata as both conduits and gatekeepers for the propagation of rapid cell‐to‐cell signaling remains a key open question. Regardless of how signals move from cell to cell, they help prepare distant parts of the plant for impending challenges from specific biotic or abiotic stresses.

    

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4. Ethylene Receptors in Nonplant Species

   https://doi.org/10.1002/smtd.201900266  

   Carlew, T. Scott ; Allen, Cidney J. ; Binder, Brad M. ( July 2019 , Small Methods)

   The effects of ethylene and ethylene signal transduction have been long studied in plants. It is only recently reported that a single‐celled cyanobacterium, Synechocystis, contains a functional ethylene receptor. However, it remains to be determined if functional ethylene receptors are more widespread. This review summarizes what is known about responses to ethylene, ethylene receptors, and signal transduction in nonplant species. A summary is provided of information gleaned from searches of sequenced genomes and the possibility that ethylene receptors are widespread in microbes is discussed.

    

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5. CPK28 is a modulator of purinergic signaling in plant growth and defense

   https://doi.org/10.1111/tpj.16656  

   Sowders, Joel M. ; Jewell, Jeremy B. ; Tanaka, Kiwamu ( February 2024 , The Plant Journal)

   Extracellular ATP (eATP) is a key signaling molecule that plays a pivotal role in plant growth and defense responses. The receptor P2K1 is responsible for perceiving eATP and initiating its signaling cascade. However, the signal transduction mechanisms downstream of P2K1 activation remain incompletely understood. We conducted a comprehensive analysis of the P2K1 interactome using co‐immunoprecipitation‐coupled tandem mass spectrometry, leading to the identification of 121 candidate proteins interacting with P2K1. In silico analysis narrowed down the candidates to 47 proteins, including Ca²⁺‐binding proteins, ion transport‐related proteins, and receptor kinases. To investigate their involvement in eATP signaling, we employed a screening strategy based on changes in gene expression in response to eATP in mutants of the identified interactors. This screening revealed several Ca²⁺‐dependent protein kinases (CPKs) that significantly affected the expression of eATP‐responsive genes, suggesting their potential roles in eATP signaling. Notably, CPK28 and CPK6 showed physical interactions with P2K1 both in yeast and plant systems. Calcium influx and gene expression studies demonstrated that CPK28 perturbed eATP‐induced Ca²⁺mobilization and some early transcriptional responses. Overexpression of CPK28 resulted in an antagonistic physiological response to P2K1‐mediated eATP signaling during both plant growth and defense responses to the necrotrophic pathogenBotrytis cinerea. Our findings highlight CPK28, among other CPKs, as a modulator of P2K1‐mediated eATP signaling, providing valuable insights into the coordination of eATP signaling in plant growth and immunity.

    

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