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Chomthong M, Griffiths H. Prospects and perspectives: inferring physiological and regulatory targets for CAM from molecular and modelling approaches. ANNALS OF BOTANY 2023; 132:583-596. [PMID: 37742290 PMCID: PMC10799989 DOI: 10.1093/aob/mcad142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Revised: 08/26/2023] [Accepted: 09/21/2023] [Indexed: 09/26/2023]
Abstract
BACKGROUND AND SCOPE This review summarizes recent advances in our understanding of Crassulacean Acid Metabolism (CAM) by integrating evolutionary, ecological, physiological, metabolic and molecular perspectives. A number of key control loops which moderate the expression of CAM phases, and their metabolic and molecular control, are explored. These include nocturnal stomatal opening, activation of phosphoenolpyruvate carboxylase by a specific protein kinase, interactions with circadian clock control, as well as daytime decarboxylation and activation of Rubisco. The vacuolar storage and release of malic acid and the interplay between the supply and demand for carbohydrate reserves are also key metabolic control points. FUTURE OPPORTUNITIES We identify open questions and opportunities, with experimentation informed by top-down molecular modelling approaches allied with bottom-up mechanistic modelling systems. For example, mining transcriptomic datasets using high-speed systems approaches will help to identify targets for future genetic manipulation experiments to define the regulation of CAM (whether circadian or metabolic control). We emphasize that inferences arising from computational approaches or advanced nuclear sequencing techniques can identify potential genes and transcription factors as regulatory targets. However, these outputs then require systematic evaluation, using genetic manipulation in key model organisms over a developmental progression, combining gene silencing and metabolic flux analysis and modelling to define functionality across the CAM day-night cycle. From an evolutionary perspective, the origins and function of CAM succulents and responses to water deficits are set against the mesophyll and hydraulic limitations imposed by cell and tissue succulence in contrasting morphological lineages. We highlight the interplay between traits across shoots (3D vein density, mesophyll conductance and cell shrinkage) and roots (xylem embolism and segmentation). Thus, molecular, biophysical and biochemical processes help to curtail water losses and exploit rapid rehydration during restorative rain events. In the face of a changing climate, we hope such approaches will stimulate opportunities for future research.
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Affiliation(s)
- Methawi Chomthong
- Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK
| | - Howard Griffiths
- Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK
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Hurtado-Castano N, Atkins E, Barnes J, Boxall SF, Dever LV, Kneřová J, Hartwell J, Cushman JC, Borland AM. The starch-deficient plastidic PHOSPHOGLUCOMUTASE mutant of the constitutive crassulacean acid metabolism (CAM) species Kalanchoë fedtschenkoi impacts diel regulation and timing of stomatal CO2 responsiveness. ANNALS OF BOTANY 2023; 132:881-894. [PMID: 36661206 PMCID: PMC10799981 DOI: 10.1093/aob/mcad017] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Accepted: 01/19/2023] [Indexed: 06/17/2023]
Abstract
BACKGROUND AND AIMS Crassulacean acid metabolism (CAM) is a specialized type of photosynthesis characterized by a diel pattern of stomatal opening at night and closure during the day, which increases water-use efficiency. Starch degradation is a key regulator of CAM, providing phosphoenolpyruvate as a substrate in the mesophyll for nocturnal assimilation of CO2. Growing recognition of a key role for starch degradation in C3 photosynthesis guard cells for mediating daytime stomatal opening presents the possibility that starch degradation might also impact CAM by regulating the provision of energy and osmolytes to increase guard cell turgor and drive stomatal opening at night. In this study, we tested the hypothesis that the timing of diel starch turnover in CAM guard cells has been reprogrammed during evolution to enable nocturnal stomatal opening and daytime closure. METHODS Biochemical and genetic characterization of wild-type and starch-deficient RNAi lines of Kalanchoë fedtschenkoi with reduced activity of plastidic phosphoglucomutase (PGM) constituted a preliminary approach for the understanding of starch metabolism and its implications for stomatal regulation in CAM plants. KEY RESULTS Starch deficiency reduced nocturnal net CO2 uptake but had negligible impact on nocturnal stomatal opening. In contrast, daytime stomatal closure was reduced in magnitude and duration in the starch-deficient rPGM RNAi lines, and their stomata were unable to remain closed in response to elevated concentrations of atmospheric CO2 administered during the day. Curtailed daytime stomatal closure was linked to higher soluble sugar contents in the epidermis and mesophyll. CONCLUSIONS Nocturnal stomatal opening is not reliant upon starch degradation, but starch biosynthesis is an important sink for carbohydrates, ensuring daytime stomatal closure in this CAM species.
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Affiliation(s)
- Natalia Hurtado-Castano
- School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE1 7RU, UK
- Plants, Photosynthesis and Soil, School of Biosciences, University of Sheffield, Sheffield S10 2TN, UK
| | - Elliott Atkins
- School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE1 7RU, UK
- John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, UK
| | - Jerry Barnes
- School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE1 7RU, UK
| | - Susanna F Boxall
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 72B, UK
| | - Louisa V Dever
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 72B, UK
| | - Jana Kneřová
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 72B, UK
| | - James Hartwell
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 72B, UK
| | - John C Cushman
- Department of Biochemistry and Molecular Biology, University of Nevada, Reno, NV 89557-0330, USA
| | - Anne M Borland
- School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE1 7RU, UK
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Nguyen TBA, Lefoulon C, Nguyen TH, Blatt MR, Carroll W. Engineering stomata for enhanced carbon capture and water-use efficiency. TRENDS IN PLANT SCIENCE 2023; 28:1290-1309. [PMID: 37423785 DOI: 10.1016/j.tplants.2023.06.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2023] [Revised: 05/29/2023] [Accepted: 06/02/2023] [Indexed: 07/11/2023]
Abstract
Stomatal pores facilitate gaseous exchange between the inner air spaces of the leaf and the atmosphere. As gatekeepers that balance CO2 entry for photosynthesis against transpirational water loss, they are a focal point for efforts to improve crop performance, especially in the efficiency of water use, within the changing global environment. Until recently, engineering strategies had focused on stomatal conductance in the steady state. These strategies are limited by the physical constraints of CO2 and water exchange such that gains in water-use efficiency (WUE) commonly come at a cost in carbon assimilation. Attention to stomatal speed and responsiveness circumvents these constraints and offers alternatives to enhancing WUE that also promise increases in carbon assimilation in the field.
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Affiliation(s)
- Thu Binh-Anh Nguyen
- Laboratory of Plant Physiology and Biophysics, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Cecile Lefoulon
- Laboratory of Plant Physiology and Biophysics, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Thanh-Hao Nguyen
- Laboratory of Plant Physiology and Biophysics, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Michael R Blatt
- Laboratory of Plant Physiology and Biophysics, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK.
| | - William Carroll
- Laboratory of Plant Physiology and Biophysics, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK
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Mimata Y, Munemasa S, Nakamura T, Nakamura Y, Murata Y. Extracellular malate induces stomatal closure via direct activation of guard-cell anion channel SLAC1 and stimulation of Ca 2+ signalling. THE NEW PHYTOLOGIST 2022; 236:852-863. [PMID: 35879859 DOI: 10.1111/nph.18400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Accepted: 07/17/2022] [Indexed: 06/15/2023]
Abstract
Plants secrete malate from guard cells to apoplast under stress conditions and exogenous malate induces stomatal closure. Malate is considered an extracellular chemical signal of stomatal closure. However, the molecular mechanism of malate-induced stomatal closure is not fully elucidated. We investigated responses of stomatal aperture, ion channels, and cytosolic Ca2+ to malate. A treatment with malate induced stomatal closure in Arabidopsis thaliana wild-type plants, but not in the mutants deficient in the slow (S-type) anion channel gene SLOW ANION CHANNEL-ASSOCIATED 1 (SLAC1). The treatment with malate increased S-type anion currents in guard-cell protoplasts of wild-type plants but not in the slac1 mutant. In addition, extracellular rather than intracellular application of malate increased the S-type currents of constitutively active mutants of SLAC1, which have kinase-independent activities, in a heterologous expression system using Xenopus oocytes. The treatment with malate transiently increased cytosolic Ca2+ concentration in the wild-type Arabidopsis guard cells and the malate-induced stomatal closure was inhibited by the Ca2+ channel blocker and the Ca2+ chelator. These results indicate that extracellular malate directly activates SLAC1 and simultaneously stimulates Ca2+ signalling in guard cells, resulting in steady and solid activation of SLAC1 for stomatal closure.
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Affiliation(s)
- Yoshiharu Mimata
- Graduate School of Environmental and Life Science, Okayama University, Tsushima-Naka 1-1-1, 700-8530, Okayama, Japan
| | - Shintaro Munemasa
- Graduate School of Environmental and Life Science, Okayama University, Tsushima-Naka 1-1-1, 700-8530, Okayama, Japan
| | - Toshiyuki Nakamura
- Graduate School of Environmental and Life Science, Okayama University, Tsushima-Naka 1-1-1, 700-8530, Okayama, Japan
| | - Yoshimasa Nakamura
- Graduate School of Environmental and Life Science, Okayama University, Tsushima-Naka 1-1-1, 700-8530, Okayama, Japan
| | - Yoshiyuki Murata
- Graduate School of Environmental and Life Science, Okayama University, Tsushima-Naka 1-1-1, 700-8530, Okayama, Japan
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Blatt MR, Jezek M, Lew VL, Hills A. What can mechanistic models tell us about guard cells, photosynthesis, and water use efficiency? TRENDS IN PLANT SCIENCE 2022; 27:166-179. [PMID: 34565672 DOI: 10.1016/j.tplants.2021.08.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Revised: 08/19/2021] [Accepted: 08/26/2021] [Indexed: 06/13/2023]
Abstract
Stomatal pores facilitate gaseous exchange between the inner air spaces of the leaf and the atmosphere. The pores open to enable CO2 entry for photosynthesis and close to reduce transpirational water loss. How stomata respond to the environment has long attracted interest in modeling as a tool to understand the consequences for the plant and for the ecosystem. Models that focus on stomatal conductance for gas exchange make intuitive sense, but such models need also to connect with the mechanics of the guard cells that regulate pore aperture if we are to understand the 'decisions made' by stomata, their impacts on the plant and on the global environment.
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Affiliation(s)
- Michael R Blatt
- Laboratory of Plant Physiology and Biophysics, University of Glasgow, Bower Building, Glasgow G12 8QQ, UK.
| | - Mareike Jezek
- Journal of Experimental Botany, Lancaster University, Lancaster LA1 4YW, UK
| | - Virgilio L Lew
- The Physiological Laboratory, University of Cambridge, Cambridge CB2 3EG, UK
| | - Adrian Hills
- Laboratory of Plant Physiology and Biophysics, University of Glasgow, Bower Building, Glasgow G12 8QQ, UK
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Draguhn A, Mallatt JM, Robinson DG. Anesthetics and plants: no pain, no brain, and therefore no consciousness. PROTOPLASMA 2021; 258:239-248. [PMID: 32880005 PMCID: PMC7907021 DOI: 10.1007/s00709-020-01550-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Accepted: 08/26/2020] [Indexed: 05/05/2023]
Abstract
Plants have a rich variety of interactions with their environment, including adaptive responses mediated by electrical signaling. This has prompted claims that information processing in plants is similar to that in animals and, hence, that plants are conscious, intelligent organisms. In several recent reports, the facts that general anesthetics cause plants to lose their sensory responses and behaviors have been taken as support for such beliefs. These lipophilic substances, however, alter multiple molecular, cellular, and systemic functions in almost every organism. In humans and other animals with complex brains, they eliminate the experience of pain and disrupt consciousness. The question therefore arises: do plants feel pain and have consciousness? In this review, we discuss what can be learned from the effects of anesthetics in plants. For this, we describe the mechanisms and structural prerequisites for pain sensations in animals and show that plants lack the neural anatomy and all behaviors that would indicate pain. By explaining the ubiquitous and diverse effects of anesthetics, we discuss whether these substances provide any empirical or logical evidence for "plant consciousness" and whether it makes sense to study the effects of anesthetics on plants for this purpose. In both cases, the answer is a resounding no.
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Affiliation(s)
- Andreas Draguhn
- Institute for Physiology and Pathophysiology, Medical Faculty, University of Heidelberg, 69120, Heidelberg, Germany
| | - Jon M Mallatt
- The University of Washington WWAMI Medical Education Program, The University of Idaho, Moscow, ID, 83844, USA
| | - David G Robinson
- Centre for Organismal Studies, University of Heidelberg, Im Neuenheimer Feld 230, D-69120, Heidelberg, Germany.
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