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1. Cyclic nucleotide‐gated ion channel 6 is involved in extracellular ATP signaling and plant immunity

   https://doi.org/10.1111/tpj.15636  

   Duong, Ha N.; Cho, Sung‐Hwan; Wang, Limin; Pham, An Q.; Davies, Julia M.; Stacey, Gary (December 2021, The Plant Journal)

   SUMMARY Extracellular ATP (eATP) is known to act as a danger signal in both plants and animals. In plants, eATP is recognized by the plasma membrane (PM)‐localized receptor P2K1 (LecRK‐I.9). Among the first measurable responses to eATP addition is a rapid rise in cytoplasmic free calcium levels ([Ca²⁺]_cyt), which requires P2K1. However, the specific transporter/channel proteins that mediate this rise in [Ca²⁺]_cytare unknown. Through a forward genetic screen, we identified an Arabidopsis ethylmethanesulfonate (EMS) mutant impaired in the [Ca²⁺]_cytresponse to eATP. Positional cloning revealed that the mutation resided in thecngc6gene, which encodes cyclic nucleotide‐gated ion channel 6 (CNGC6). Mutation of theCNGC6gene led to a notable decrease in the PM inward Ca²⁺current in response to eATP. eATP‐induced mitogen‐activated protein kinase activation and gene expression were also significantly lower incngc6mutant plants. In addition,cngc6mutant plants were also more susceptible to the bacterial pathogenPseudomonas syringae. Taken together, our results indicate that CNGC6 plays a crucial role in mediating eATP‐induced [Ca²⁺]_cytsignaling, as well as plant immunity. 

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2. The Arabidopsis heterotrimeric G‐protein β subunit, AGB 1, is required for guard cell calcium sensing and calcium‐induced calcium release

   https://doi.org/10.1111/tpj.14318  

   Jeon, Byeong Wook; Acharya, Biswa R.; Assmann, Sarah M. (April 2019, The Plant Journal)

   <bold>Summary</bold> Cytosolic calcium concentration ([Ca²⁺]_cyt) and heterotrimeric G‐proteins are universal eukaryotic signaling elements. In plant guard cells, extracellular calcium (Ca_o) is as strong a stimulus for stomatal closure as the phytohormone abscisic acid (ABA), but underlying mechanisms remain elusive. Here, we report that the sole Arabidopsis heterotrimeric Gβ subunit,AGB1, is required for four guard cell Ca_oresponses: induction of stomatal closure; inhibition of stomatal opening; [Ca²⁺]_cytoscillation; and inositol 1,4,5‐trisphosphate (InsP3) production. Stomata in wild‐type Arabidopsis (Col) and in mutants of the canonical Gα subunit,GPA1, showed inhibition of stomatal opening and promotion of stomatal closure by Ca_o. By contrast, stomatal movements ofagb1mutants andagb1/gpa1double‐mutants, as well as those of theagg1agg2 Gγ double‐mutant, were insensitive to Ca_o. These behaviors contrast withABA‐regulated stomatal movements, which involveGPA1 andAGB1/AGG3 dimers, illustrating differential partitioning of G‐protein subunits among stimuli with similar ultimate impacts, which may facilitate stimulus‐specific encoding.AGB1knockouts retained reactive oxygen species andNOproduction, but lostYC3.6‐detected [Ca²⁺]_cytoscillations in response to Ca_o, initiating only a single [Ca²⁺]_cytspike. Experimentally imposed [Ca²⁺]_cytoscillations restored stomatal closure inagb1. Yeast two‐hybrid and bimolecular complementation fluorescence experiments revealed thatAGB1 interacts with phospholipase Cs (PLCs), and Ca_oinduced InsP3 production in Col but not inagb1. In sum, G‐protein signaling viaAGB1/AGG1/AGG2 is essential for Ca_o‐regulation of stomatal apertures, and stomatal movements in response to Ca_oapparently require Ca²⁺‐induced Ca²⁺release that is likely dependent on Gβγ interaction withPLCs leading to InsP3 production. 

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3. Jasmonate primes plant responses to extracellular ATP

   https://doi.org/10.1111/tpj.70514  

   Jewell, Jeremy_B; Carlton, Ashleigh_S; Tolley, Jordan_P; Bartley, Laura_E; Tanaka, Kiwamu (October 2025, The Plant Journal)

   SUMMARY Extracellular ATP (eATP) signaling inArabidopsis thalianais mediated by the purinoceptor P2K1. Previous studies have clarified that the downstream transcriptional responses to eATP involve jasmonate (JA)‐based signaling components such as the JA receptor (COI1) and JA‐responsive bHLH transcription factors (MYCs). However, the specific contributions of JA itself on eATP signaling are unexplored. Here, we report that JA primes plant responses to eATP through P2K1. Our findings show that JA treatment significantly upregulatesP2K1transcription, corroborating our observation that JA facilitates eATP‐induced cytosolic calcium elevation and transcriptional reprogramming in a JA signaling‐dependent manner. Additionally, we find that salicylic acid pre‐treatment represses eATP‐induced plant response. These results suggest that JA accumulation during biotic or abiotic stresses potentiates eATP signaling, enabling plants to better cope with subsequent stress events. 

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4. Jasmonate Primes Plant Responses to Extracellular ATP

   https://doi.org/10.1101/2024.11.07.622526  

   Jewell, Jeremy B; Carlton, Ashleigh S; Tolley, Jordan P; Bartley, Laura E; Tanaka, Kiwamu (September 2025, The Plant Journal)

   Extracellular ATP (eATP) signaling inArabidopsis thalianais mediated by the purinoceptor P2K1. Previous studies have clarified that the downstream transcriptional responses to eATP involve jasmonate (JA)-based signaling components such as the JA receptor (COI1) and JA-responsive bHLH transcription factors (MYCs). However, the specific contributions of JA signaling itself on eATP signaling are unexplored. Here, we report that JA primes plant responses to eATP through P2K1. Our findings show that JA treatment significantly upregulatesP2K1transcription, corroborating our observation that JA facilitates eATP-induced cytosolic calcium elevation and transcriptional reprogramming in a JA signaling-dependent manner. Additionally, we find that salicylic acid pretreatment represses eATP-induced plant response. These results suggest that JA accumulation during biotic or abiotic stresses may potentiate eATP signaling, enabling plants to better cope with subsequent stress events. Plant hormone jasmonate (JA) enhances plant responses to extracellular ATP (eATP) inArabidopsis thalianathrough a mechanism dependent on the JA receptor COI1 and the eATP receptor P2K1. The reciprocal amplification of these signals provides a mechanistic explanation for how plants effectively respond to different stress events. 

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5. A role for calcium‐dependent protein kinases in differential CO ₂ ‐ and ABA‐controlled stomatal closing and low CO ₂ ‐induced stomatal opening in Arabidopsis

   https://doi.org/10.1111/nph.17079  

   Schulze, Sebastian; Dubeaux, Guillaume; Ceciliato, Paulo H. O.; Munemasa, Shintaro; Nuhkat, Maris; Yarmolinsky, Dmitry; Aguilar, Jaimee; Diaz, Renee; Azoulay‐Shemer, Tamar; Steinhorst, Leonie; et al (December 2020, New Phytologist)

   Summary Low concentrations of CO₂cause stomatal opening, whereas [CO₂] elevation leads to stomatal closure. Classical studies have suggested a role for Ca²⁺and protein phosphorylation in CO₂‐induced stomatal closing. Calcium‐dependent protein kinases (CPKs) and calcineurin‐B‐like proteins (CBLs) can sense and translate cytosolic elevation of the second messenger Ca²⁺into specific phosphorylation events. However, Ca²⁺‐binding proteins that function in the stomatal CO₂response remain unknown.Time‐resolved stomatal conductance measurements using intact plants, and guard cell patch‐clamp experiments were performed.We isolatedcpkquintuple mutants and analyzed stomatal movements in response to CO₂, light and abscisic acid (ABA). Interestingly, we found thatcpk3/5/6/11/23quintuple mutant plants, but not other analyzedcpkquadruple/quintuple mutants, were defective in high CO₂‐induced stomatal closure and, unexpectedly, also in low CO₂‐induced stomatal opening. Furthermore, K⁺‐uptake‐channel activities were reduced incpk3/5/6/11/23quintuple mutants, in correlation with the stomatal opening phenotype. However, light‐mediated stomatal opening remained unaffected, and ABA responses showed slowing in some experiments. By contrast, CO₂‐regulated stomatal movement kinetics were not clearly affected in plasma membrane‐targetedcbl1/4/5/8/9quintuple mutant plants.Our findings describe combinatorialcpkmutants that function in CO₂control of stomatal movements and support the results of classical studies showing a role for Ca²⁺in this response. 

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