Chloroplast-Specific in Vivo Ca<sup>2+</sup> Imaging Using Yellow Cameleon Fluorescent Protein Sensors Reveals Organelle-Autonomous Ca<sup>2+</sup> Signatures in the Stroma

Loro, Giovanna; Wagner, Stephan; Doccula, Fabrizio Gandolfo; Behera, Smrutisanjita; Weinl, Stefan; Kudla, Jörg; Schwarzländer, Markus; Costa, Alex; Zottini, Michela

doi:10.1104/pp.16.00652

Cited by 73 publications

(78 citation statements)

References 69 publications

(100 reference statements)

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“…The usage of genetically encoded biosensors has the potential to overcome several critical hurdles and deliver information from the upstream end of signaling, similarly to what transcript analysis achieves at the downstream end. Sensors for some of the promising candidates of mitochondrial signaling stimuli have been created or adapted for use in plants and an understanding of the cell-compartment-specific in vivo dynamics of several of the molecules discussed here has moved into reach, including H 2 O 2 , ATP, and Ca 2+ (Costa et al, 2010;Loro et al, 2012Loro et al, , 2016Bonza et al, 2013;De Col et al, 2017). A next major step forward is likely to come from measuring the dynamics of a large array of chemical species in concert.…”

Section: Resultsmentioning

confidence: 99%

Mitochondrial Energy Signaling and Its Role in the Low-Oxygen Stress Response of Plants

et al. 2018

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ORCID IDs: 0000-0001-5369-7911 (S.W.); 0000-0003-4024-968X (O.V.A.); 0000-0003-0796-8308 (M.S.).Cells of complex organisms typically rely on mitochondria for energy provision. The amount of energy required to sustain cellular activity can vary strongly depending on external conditions. Vice versa, constraints on respiratory activity due to metabolic status or stress insult require mitochondrial signaling to coordinate cellular physiology with the function of the organelle. In this update, we review recent insights into plant mitochondrial energy signaling in the light of their significance to stress acclimation. First, we focus on the characteristic adjustments of the nuclear transcriptome that occur after pharmacological inhibition of the mitochondrial electron transport chain as the output of mitochondrial retrograde signaling. Second, we discuss the proteins that have recently been identified as regulators of the transcript responses and the emerging picture of their action as a signaling network. We then pose the question of how well our current models of inducing mitochondrial dysfunction relate to conditions that plants face naturally. We reason that low-oxygen stress shows striking similarities with electron transport inhibitors with respect to their impact on mitochondrial energy physiology upstream, as well as the cellular transcriptomic response. Finally, we highlight and discuss changes in mitochondrial physiology that are common to both stimuli as candidates for upstream signals. The aim of this update is to better define the physiological context in which mitochondrial signaling operates to provide new directions for future research. RESPONSES TO MITOCHONDRIAL ENERGY SIGNALING AT THE TRANSCRIPT LEVEL

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Section: Resultsmentioning

confidence: 99%

Mitochondrial Energy Signaling and Its Role in the Low-Oxygen Stress Response of Plants

et al. 2018

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“…Alternatively, the ultrastructural or physiological defects entailed by the bicat2 mutation may render BICAT1 nonfunctional. The availability of single and double mutants for BICAT1 and BICAT2, together with novel reporters for chloroplast subcompartments (Loro et al, 2016;Sello et al, 2018), now allows the dissection of Ca 2+ fluxes and Ca 2+ storage during light phase and light-dark transitions, thus putting the alternative models to the test.…”

Section: Discussionmentioning

confidence: 99%

“…Many processes associated with photosynthesis need to be controlled during the natural light–dark cycles, and Ca 2+ has the capability to act as such a coordinating signal due to the numerous potential targets of Ca 2+ in the chloroplast. In line with this notion, changes in the level of free Ca 2+ in the chloroplast stroma ([Ca 2+ ] stroma ) upon the onset of darkness have been observed by employing the luminescent reporter protein aequorin (Johnson et al ., ; Sai & Johnson, ; Nomura et al ., ; Sello et al ., ) or the ratiometric reporter protein Yellow Cameleon 3.6 (Loro et al ., ). Based on the Ca 2+ ‐sensitivity of Calvin–Benson–Bassham cycle enzymes, these darkness‐induced [Ca 2+ ] stroma elevations have been proposed to signal the cessation of CO 2 fixation (Johnson et al ., ; Sai & Johnson, ).…”

Section: Introductionmentioning

confidence: 97%

Chloroplast‐localized BICAT proteins shape stromal calcium signals and are required for efficient photosynthesis

et al. 2018

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The photosynthetic machinery of plants must be regulated to maximize the efficiency of light reactions and CO fixation. Changes in free Ca in the stroma of chloroplasts have been observed at the transition between light and darkness, and also in response to stress stimuli. Such Ca dynamics have been proposed to regulate photosynthetic capacity. However, the molecular mechanisms of Ca fluxes in the chloroplasts have been unknown. By employing a Ca reporter-based approach, we identified two chloroplast-localized Ca transporters in Arabidopsis thaliana, BICAT1 and BICAT2, that determine the amplitude of the darkness-induced Ca signal in the chloroplast stroma. BICAT2 mediated Ca uptake across the chloroplast envelope, and its knockout mutation strongly dampened the dark-induced [Ca ] signal. Conversely, this Ca transient was increased in knockout mutants of BICAT1, which transports Ca into the thylakoid lumen. Knockout mutation of BICAT2 caused severe defects in chloroplast morphology, pigmentation and photosynthetic light reactions, rendering bicat2 mutants barely viable under autotrophic growth conditions, while bicat1 mutants were less affected. These results show that BICAT transporters play a role in chloroplast Ca homeostasis. They are also involved in the regulation of photosynthesis and plant productivity. Further work will be required to reveal whether the effect on photosynthesis is a direct result of their role as Ca transporters.

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“…Additionally, root leucoplasts have intracellular membranous lamellar vesicles and plastoglobules (56), the latter of which has significant association with thylakoids in terms of proteome composition (57). Indeed, a recent publication demonstrates the existence of root plastid calcium signaling in response to various chemical stimuli (58). Thus, the calcium signaling phenotype found in the kea mutants may be attributable to disrupted root plastid ion homeostasis, but presently an indirect effect (leaf-to-root) or systemic effect cannot be excluded and will require further analyses.…”

Section: Discussionmentioning

confidence: 99%

Rapid hyperosmotic-induced Ca ²⁺ responses in Arabidopsis thaliana exhibit sensory potentiation and involvement of plastidial KEA transporters

Stephan

Kunz

Yang

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Plants experience hyperosmotic stress when faced with saline soils and possibly with drought stress, but it is currently unclear how plant roots perceive this stress in an environment of dynamic water availabilities. Hyperosmotic stress induces a rapid rise in intracellular Ca 2+ concentrations ([Ca 2+ ] i ) in plants, and this Ca 2+ response may reflect the activities of osmo-sensory components. Here, we find in the reference plant Arabidopsis thaliana that the rapid hyperosmoticinduced Ca 2+ response exhibited enhanced response magnitudes after preexposure to an intermediate hyperosmotic stress. We term this phenomenon "osmo-sensory potentiation." The initial sensing and potentiation occurred in intact plants as well as in roots. Having established a quantitative understanding of wild-type responses, we investigated effects of pharmacological inhibitors and candidate channel/transporter mutants. Quintuple mechano-sensitive channels of small conductance-like (MSL) plasma membrane-targeted channel mutants as well as double mid1-complementing activity (MCA) channel mutants did not affect the response. Interestingly, however, double mutations in the plastid K + exchange antiporter (KEA) transporters kea1kea2 and a single mutation that does not visibly affect chloroplast structure, kea3, impaired the rapid hyperosmotic-induced Ca 2+ responses. These mutations did not significantly affect sensory potentiation of the response. These findings suggest that plastids may play an important role in early steps mediating the response to hyperosmotic stimuli. Together, these findings demonstrate that the plant osmosensory components necessary to generate rapid osmotic-induced Ca 2+ responses remain responsive under varying osmolarities, endowing plants with the ability to perceive the dynamic intensities of water limitation imposed by osmotic stress.osmotic sensing | calcium | salt stress | plastid | abscisic acid P lants exhibit a wide range of physiological responses to cope with water deprivation by drought and salinity stress (1-3). The properties of biological sensors determine the circumstances and extent to which these coping mechanisms are activated, but the early sensory mechanisms and components regulating the osmotic sensory components in plants are not well understood (see ref. 4 for review). Pioneering studies have demonstrated that Arabidopsis seedlings expressing the bioluminescent Ca 2+ reporter protein aequorin exhibit a rapid rise in intracellular Ca 2+ ([Ca 2+ ] i ) within seconds upon stimulation by NaCl solution (5, 6). This rapid osmotic-induced Ca 2+ response has been observed in plant species ranging from rice (7) to the basal-branching moss taxon Physcomitrella patens (8), indicating that this response may be conserved across the Plantae kingdom. Solutions of either NaCl or isoosmotic mannitol/sorbitol induce nearly identical rapid Ca 2+ responses, indicating that the nature of this rapid stimulus is largely osmotic rather than ionic (5, 9, 10). Individual seedling responses tend to be quite hetero...

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Chloroplast-Specific in Vivo Ca²⁺ Imaging Using Yellow Cameleon Fluorescent Protein Sensors Reveals Organelle-Autonomous Ca²⁺ Signatures in the Stroma

Cited by 73 publications

References 69 publications

Mitochondrial Energy Signaling and Its Role in the Low-Oxygen Stress Response of Plants

Mitochondrial Energy Signaling and Its Role in the Low-Oxygen Stress Response of Plants

Chloroplast‐localized BICAT proteins shape stromal calcium signals and are required for efficient photosynthesis

Rapid hyperosmotic-induced Ca ²⁺ responses in Arabidopsis thaliana exhibit sensory potentiation and involvement of plastidial KEA transporters

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Chloroplast-Specific in Vivo Ca2+ Imaging Using Yellow Cameleon Fluorescent Protein Sensors Reveals Organelle-Autonomous Ca2+ Signatures in the Stroma

Cited by 73 publications

References 69 publications

Mitochondrial Energy Signaling and Its Role in the Low-Oxygen Stress Response of Plants

Mitochondrial Energy Signaling and Its Role in the Low-Oxygen Stress Response of Plants

Chloroplast‐localized BICAT proteins shape stromal calcium signals and are required for efficient photosynthesis

Rapid hyperosmotic-induced Ca 2+ responses in Arabidopsis thaliana exhibit sensory potentiation and involvement of plastidial KEA transporters

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Chloroplast-Specific in Vivo Ca²⁺ Imaging Using Yellow Cameleon Fluorescent Protein Sensors Reveals Organelle-Autonomous Ca²⁺ Signatures in the Stroma

Rapid hyperosmotic-induced Ca ²⁺ responses in Arabidopsis thaliana exhibit sensory potentiation and involvement of plastidial KEA transporters