More Like this

1. 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)

   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.

    

   more » « less
2. GSK 3‐like kinase BIN 2 phosphorylates RD 26 to potentiate drought signaling in Arabidopsis

   https://doi.org/10.1111/tpj.14484  

   Jiang, Hao ; Tang, Buyun ; Xie, Zhouli ; Nolan, Trevor ; Ye, Huaxun ; Song, Gao‐Yuan ; Walley, Justin ; Yin, Yanhai ( August 2019 , The Plant Journal)

   Plant steroid hormones brassinosteroids (BRs) regulate plant growth and development at many different levels. Recent research has revealed that stress‐responsive NAC (petunia NAM and Arabidopsis ATAF1, ATAF2, and CUC2) transcription factorRD26 is regulated byBRsignaling and antagonizesBES1 in the interaction between growth and drought stress signaling. However, the upstream signaling transduction components that activateRD26 during drought are still unknown. Here, we demonstrate that the function ofRD26 is modulated byGSK3‐like kinaseBIN2 and protein phosphatase 2CABI1. We show thatABI1, a negative regulator inabscisic acid (ABA)signaling, dephosphorylates and destabilizesBIN2 to inhibitBIN2 kinase activity.RD26 protein is stabilized byABAand dehydration in aBIN2‐dependent manner.BIN2 directly interacts and phosphorylatesRD26in vitroandin vivo.BIN2 phosphorylation ofRD26 is required forRD26 transcriptional activation on drought‐responsive genes.RD26 overexpression suppressed the brassinazole (BRZ)  insensitivity ofBIN2 triple mutantbin2 bil1 bil2, andBIN2 function is required for the drought tolerance ofRD26 overexpression plants. Taken together, our data suggest a drought signaling mechanism in which drought stress relievesABI1 inhibition ofBIN2, allowingBIN2 activation. Sequentially,BIN2 phosphorylates and stabilizesRD26 to promote drought stress response.

    

   more » « less
3. SNP discovery in candidate adaptive genes using exon capture in a free‐ranging alpine ungulate

   https://doi.org/10.1111/1755-0998.12560  

   Roffler, Gretchen H. ; Amish, Stephen J. ; Smith, Seth ; Cosart, Ted ; Kardos, Marty ; Schwartz, Michael K. ; Luikart, Gordon ( July 2016 , Molecular Ecology Resources)

   Identification of genes underlying genomic signatures of natural selection is key to understanding adaptation to local conditions. We used targeted resequencing to identifySNPmarkers in 5321 candidate adaptive genes associated with known immunological, metabolic and growth functions in ovids and other ungulates. We selectively targeted 8161 exons in protein‐coding and nearby 5′ and 3′ untranslated regions of chosen candidate genes. Targeted sequences were taken from bighorn sheep (Ovis canadensis) exon capture data and directly from the domestic sheep genome (Ovis ariesv. 3; oviAri3). The bighorn sheep sequences used in the Dall's sheep (Ovis dalli dalli) exon capture aligned to 2350 genes on the oviAri3 genome with an average of 2 exons each. We developed a microfluidic qPCR‐basedSNPchip to genotype 476 Dall's sheep from locations across their range and test for patterns of selection. Using multiple corroborating approaches (lositanandbayescan), we detected 28SNPloci potentially under selection. We additionally identified candidate loci significantly associated with latitude, longitude, precipitation and temperature, suggesting local environmental adaptation. The three methods demonstrated consistent support for natural selection on nine genes with immune and disease‐regulating functions (e.g. Ovar‐DRA,APC,BATF2,MAGEB18), cell regulation signalling pathways (e.g.KRIT1,PI3K,ORRC3), and respiratory health (CYSLTR1). Characterizing adaptive allele distributions from novel genetic techniques will facilitate investigation of the influence of environmental variation on local adaptation of a northern alpine ungulate throughout its range. This research demonstrated the utility of exon capture for gene‐targetedSNPdiscovery and subsequentSNPchip genotyping using low‐quality samples in a nonmodel species.

    

   more » « less
4. Mitogen‐activated protein kinases MPK 4 and MPK 12 are key components mediating CO 2 ‐induced stomatal movements

   https://doi.org/10.1111/tpj.14087  

   Tõldsepp, Kadri ; Zhang, Jingbo ; Takahashi, Yohei ; Sindarovska, Yana ; Hõrak, Hanna ; Ceciliato, Paulo H. O. ; Koolmeister, Kaspar ; Wang, Yuh‐Shuh ; Vaahtera, Lauri ; Jakobson, Liina ; et al ( October 2018 , The Plant Journal)

   Respiration in leaves and the continued elevation in the atmosphericCO₂concentration causeCO₂‐mediated reduction in stomatal pore apertures. Several mutants have been isolated for which stomatal responses to both abscisic acid (ABA) andCO₂are simultaneously defective. However, there are only few mutations that impair the stomatal response to elevatedCO₂, but not toABA. Such mutants are invaluable in unraveling the molecular mechanisms of earlyCO₂signal transduction in guard cells. Recently, mutations in the mitogen‐activated protein (MAP) kinase,MPK12, have been shown to partially impairCO₂‐induced stomatal closure. Here, we show thatmpk12plants, in whichMPK4is stably silenced specifically in guard cells (mpk12 mpk4GChomozygous double‐mutants), completely lackCO₂‐induced stomatal responses and have impaired activation of guard cell S‐type anion channels in response to elevatedCO₂/bicarbonate. However,ABA‐induced stomatal closure, S‐type anion channel activation andABA‐induced marker gene expression remain intact in thempk12 mpk4GCdouble‐mutants. These findings suggest thatMPK12 andMPK4 act very early inCO₂signaling, upstream of, or parallel to the convergence ofCO₂andABAsignal transduction. The activities ofMPK4 andMPK12 protein kinases were not directly modulated byCO₂/bicarbonatein vitro, suggesting that they are not directCO₂/bicarbonate sensors. Further data indicate thatMPK4 andMPK12 have distinguishable roles in Arabidopsis and that the previously suggested role ofRHC1 in stomatalCO₂signaling is minor, whereasMPK4 andMPK12 act as key components of early stomatalCO₂signal transduction.

    

   more » « less
5. 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.

    

   more » « less