More Like this

1. Arabidopsis thaliana CYCLIC NUCLEOTIDE‐GATED CHANNEL2 mediates extracellular ATP signal transduction in root epidermis

   https://doi.org/10.1111/nph.17987  

   Wang, Limin ; Ning, Youzheng ; Sun, Jian ; Wilkins, Katie A. ; Matthus, Elsa ; McNelly, Rose E. ; Dark, Adeeba ; Rubio, Lourdes ; Moeder, Wolfgang ; Yoshioka, Keiko ; et al ( February 2022 , New Phytologist)

   Damage can be signalled by extracellular ATP (eATP) using plasma membrane (PM) receptors to effect cytosolic free calcium ion ([Ca²⁺]_cyt) increase as a second messenger. The downstream PM Ca²⁺channels remain enigmatic. Here, theArabidopsis thalianaCa²⁺channel subunit CYCLIC NUCLEOTIDE‐GATED CHANNEL2 (CNGC2) was identified as a critical component linking eATP receptors to downstream [Ca²⁺]_cytsignalling in roots.

   Extracellular ATP‐induced changes in single epidermal cell PM voltage and conductance were measured electrophysiologically, changes in root [Ca²⁺]_cytwere measured with aequorin, and root transcriptional changes were determined by quantitative real‐time PCR. Twocngc2loss‐of‐function mutants were used:cngc2‐3anddefence not death1(which expresses cytosolic aequorin).

   Extracellular ATP‐induced transient depolarization of Arabidopsis root elongation zone epidermal PM voltage was Ca²⁺dependent, requiring CNGC2 but not CNGC4 (its channel co‐subunit in immunity signalling). Activation of PM Ca²⁺influx currents also required CNGC2. The eATP‐induced [Ca²⁺]_cytincrease and transcriptional response incngc2roots were significantly impaired.

   CYCLIC NUCLEOTIDE‐GATED CHANNEL2 is required for eATP‐induced epidermal Ca²⁺influx, causing depolarization leading to [Ca²⁺]_cytincrease and damage‐related transcriptional response.

    

   more » « less
2. Plant “helper” immune receptors are Ca 2+ -permeable nonselective cation channels

   https://doi.org/10.1126/science.abg7917  

   Jacob, Pierre ; Kim, Nak Hyun ; Wu, Feihua ; El-Kasmi, Farid ; Chi, Yuan ; Walton, William G. ; Furzer, Oliver J. ; Lietzan, Adam D. ; Sunil, Sruthi ; Kempthorn, Korina ; et al ( June 2021 , Science)

   Plant nucleotide-binding leucine-rich repeat receptors (NLRs) regulate immunity and cell death. InArabidopsis, a subfamily of “helper” NLRs is required by many “sensor” NLRs. Active NRG1.1 oligomerized, was enriched in plasma membrane puncta, and conferred cytoplasmic calcium ion (Ca²⁺) influx in plant and human cells. NRG1.1-dependent Ca²⁺influx and cell death were sensitive to Ca²⁺channel blockers and were suppressed by mutations affecting oligomerization or plasma membrane enrichment. Ca²⁺influx and cell death mediated by NRG1.1 and ACTIVATED DISEASE RESISTANCE 1 (ADR1), another helper NLR, required conserved negatively charged N-terminal residues. Whole-cell voltage-clamp recordings demonstrated thatArabidopsishelper NLRs form Ca²⁺-permeable cation channels to directly regulate cytoplasmic Ca²⁺levels and consequent cell death. Thus, helper NLRs transduce cell death signals directly.

    

   more » « less
3. The vacuolar Ca 2+ transporter CATION EXCHANGER 2 regulates cytosolic calcium homeostasis, hypoxic signaling, and response to flooding in Arabidopsis thaliana

   https://doi.org/10.1111/nph.19274  

   Bakshi, Arkadipta ; Choi, Won‐Gyu ; Kim, Su‐Hwa ; Gilroy, Simon ( September 2023 , New Phytologist)

   Flooding represents a major threat to global agricultural productivity and food security, but plants are capable of deploying a suite of adaptive responses that can lead to short‐ or longer‐term survival to this stress. One cellular pathway thought to help coordinate these responses is via flooding‐triggered Ca²⁺signaling.

   We have mined publicly available transcriptomic data from Arabidopsis subjected to flooding or low oxygen stress to identify rapidly upregulated, Ca²⁺‐related transcripts. We then focused on transporters likely to modulate Ca²⁺signals. Candidates emerging from this analysis includedAUTOINHIBITED Ca²⁺ATPASE 1andCATION EXCHANGER 2. We therefore assayed mutants in these genes for flooding sensitivity at levels from growth to patterns of gene expression and the kinetics of flooding‐related Ca²⁺changes.

   Knockout mutants inCAX2especially showed enhanced survival to soil waterlogging coupled with suppressed induction of many marker genes for hypoxic response and constitutive activation of others.CAX2mutants also generated larger and more sustained Ca²⁺signals in response to both flooding and hypoxic challenges.

   CAX2 is a Ca²⁺transporter located on the tonoplast, and so these results are consistent with an important role for vacuolar Ca²⁺transport in the signaling systems that trigger flooding response.

    

   more » « less
4. Cell death signaling in Anopheles gambiae initiated by Bacillus thuringiensis Cry4B toxin involves Na + /K + ATPase

   https://doi.org/10.1177/15353702231188072  

   Liu, Li ; Bulla, Jr, Lee A. ( August 2023 , Experimental Biology and Medicine)

   Identifying the mechanisms by which bacterial pathogens kill host cells is fundamental to understanding how to control and prevent human and animal disease. In the case of Bacillus thuringiensis (Bt), such knowledge is critical to using the bacterium to kill insect vectors that transmit human and animal disease. For the Cry4B toxin produced by Bt, its capacity to kill Anopheles gambiae, the primary mosquito vector of malaria, is the consequence of a variety of signaling activities. We show here that Cry4B, acting as first messenger, binds specifically to the bitopic cadherin BT-R₃G-protein-coupled receptor (GPCR) localized in the midgut of A. gambiae, activating the downstream second messenger cyclic adenosine monophosphate (cAMP). The direct result of the Cry4B–BT-R₃binding is the release of α_sfrom the heterotrimeric αβγ-G-protein complex and its activation of adenylyl cyclase (AC). The upshot is an increased level of cAMP, which activates protein kinase A (PKA). The functional impact of cAMP–PKA signaling is the stimulation of Na⁺/K⁺-ATPase (NKA) which serves as an Na⁺/K⁺pump to maintain proper gradients of extracellular Na⁺and intracellular K⁺. Increased level of cAMP amplifies NKA and upsets normal ion concentration gradients. NKA, as a scaffolding protein, accelerates the first messenger signal to the nucleus, generating additional BT-R₃molecules and promoting their exocytotic trafficking to the cell membrane. Accumulation of BT-R₃on the cell surface facilitates recruitment of additional toxin molecules which, in turn, amplify the original signal in a cascade-like manner. This report provides the first evidence of a bacterial toxin using NKA via AC/PKA signaling to execute cell death.

    

   more » « less
5. 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.

    

   more » « less