TY  - JOUR
A1  - Huang, Shouguang
A1  - Waadt, Rainer
A1  - Nuhkat, Maris
A1  - Kollist, Hannes
A1  - Hedrich, Rainer
A1  - Roelfsema, M. Rob G.
T1  - Calcium signals in guard cells enhance the efficiency by which abscisic acid triggers stomatal closure
JF  - New Phytologist
N2  - During drought, abscisic acid (ABA) induces closure of stomata via a signaling pathway that involves the calcium (Ca2+)-independent protein kinase OST1, as well as Ca2+-dependent protein kinases. However, the interconnection between OST1 and Ca2+ signaling in ABA-induced stomatal closure has not been fully resolved.

ABA-induced Ca2+ signals were monitored in intact Arabidopsis leaves, which express the ratiometric Ca2+ reporter R-GECO1-mTurquoise and the Ca2+-dependent activation of S-type anion channels was recorded with intracellular double-barreled microelectrodes.

ABA triggered Ca2+ signals that occurred during the initiation period, as well as in the acceleration phase of stomatal closure. However, a subset of stomata closed in the absence of Ca2+ signals. On average, stomata closed faster if Ca2+ signals were elicited during the ABA response. Loss of OST1 prevented ABA-induced stomatal closure and repressed Ca2+ signals, whereas elevation of the cytosolic Ca2+ concentration caused a rapid activation of SLAC1 and SLAH3 anion channels.

Our data show that the majority of Ca2+ signals are evoked during the acceleration phase of stomatal closure, which is initiated by OST1. These Ca2+ signals are likely to activate Ca2+-dependent protein kinases, which enhance the activity of S-type anion channels and boost stomatal closure.
KW  - abscisic acid (ABA)
KW  - Ca2+- indicator
KW  - cytosolic Ca2+ signals
KW  - OST1 protein kinase
KW  - R-GECO1-mTurquoise
KW  - SLAC1 and SLAH3 anion channels
KW  - stomata
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-322716
VL  - 224
ER  - 
TY  - JOUR
A1  - Jakobson, Liina
A1  - Vaahtera, Lauri
A1  - Tõldsepp, Kadri
A1  - Nuhkat, Maris
A1  - Wang, Cun
A1  - Wang, Yuh-Shuh
A1  - Hõrak, Hanna
A1  - Valk, Ervin
A1  - Pechter, Priit
A1  - Sindarovska, Yana
A1  - Tang, Jing
A1  - Xiao, Chuanlei
A1  - Xu, Yang
A1  - Talas, Ulvi Gerst
A1  - García-Sosa, Alfonso T.
A1  - Kangasjärvi, Saijaliisa
A1  - Maran, Uko
A1  - Remm, Maido
A1  - Roelfsema, M. Rob G.
A1  - Hu, Honghong
A1  - Kangasjärvi, Jaakko
A1  - Loog, Mart
A1  - Schroeder, Julian I.
A1  - Kollist, Hannes
A1  - Brosché, Mikael
T1  - Natural Variation in Arabidopsis Cvi-0 Accession Reveals an Important Role of MPK12 in Guard Cell CO\(_{2}\) Signaling
JF  - PLoS Biology
N2  - Plant gas exchange is regulated by guard cells that form stomatal pores. Stomatal adjustments are crucial for plant survival; they regulate uptake of CO\(_{2}\) for photosynthesis, loss of water, and entrance of air pollutants such as ozone. We mapped ozone hypersensitivity, more open stomata, and stomatal CO\(_{2}\)-insensitivity phenotypes of the Arabidopsis thaliana accession Cvi-0 to a single amino acid substitution in MITOGEN-ACTIVATED PROTEIN (MAP) KINASE 12 (MPK12). In parallel, we showed that stomatal CO\(_{2}\)-insensitivity phenotypes of a mutant cis (CO\(_{2}\)-insensitive) were caused by a deletion of MPK12. Lack of MPK12 impaired bicarbonate-induced activation of S-type anion channels. We demonstrated that MPK12 interacted with the protein kinase HIGH LEAF TEMPERATURE 1 (HT1)—a central node in guard cell CO\(_{2}\) signaling—and that MPK12 functions as an inhibitor of HT1. These data provide a new function for plant MPKs as protein kinase inhibitors and suggest a mechanism through which guard cell CO\(_{2}\) signaling controls plant water management.
KW  - MPK12
KW  - CO\(_{2}\) signaling
KW  - Arabidopsis thaliana
KW  - Cvi-0
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-166657
VL  - 14
IS  - 12
ER  - 
TY  - JOUR
A1  - Nuhkat, Maris
A1  - Brosché, Mikael
A1  - Stoezle-Feix, Sonja
A1  - Dietrich, Petra
A1  - Hedrich, Rainer
A1  - Roelfsema, M. Rob G.
A1  - Kollist, Hannes
T1  - Rapid depolarization and cytosolic calcium increase go hand-in-hand in mesophyll cells' ozone response
JF  - New Phytologist
N2  - Plant stress signalling involves bursts of reactive oxygen species (ROS), which can be mimicked by the application of acute pulses of ozone. Such ozone-pulses inhibit photosynthesis and trigger stomatal closure in a few minutes, but the signalling that underlies these responses remains largely unknown.
We measured changes in Arabidopsis thaliana gas exchange after treatment with acute pulses of ozone and set up a system for simultaneous measurement of membrane potential and cytosolic calcium with the fluorescent reporter R-GECO1.
We show that within 1 min, prior to stomatal closure, O\(_{3}\) triggered a drop in whole-plant CO\(_{2}\) uptake. Within this early phase, O\(_{3}\) pulses (200–1000 ppb) elicited simultaneous membrane depolarization and cytosolic calcium increase, whereas these pulses had no long-term effect on either stomatal conductance or photosynthesis. In contrast, pulses of 5000 ppb O\(_{3}\) induced cell death, systemic Ca\(^{2+}\) signals and an irreversible drop in stomatal conductance and photosynthetic capacity.
We conclude that mesophyll cells respond to ozone in a few seconds by distinct pattern of plasma membrane depolarizations accompanied by an increase in the cytosolic calcium ion (Ca\(^{2+}\)) level. These responses became systemic only at very high ozone concentrations. Thus, plants have rapid mechanism to sense and discriminate the strength of ozone signals.
KW  - reactive oxygen species (ROS)
KW  - Arabidopsis thaliana
KW  - Ca\(^{2+}\) indicator
KW  - Ca\(^{2+}\) signalling
KW  - membrane depolarization
KW  - mesophyll
KW  - ozone
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-259646
VL  - 232
IS  - 4
ER  -