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<bold>Summary</bold> Cytosolic calcium concentration ([Ca2+]cyt) and heterotrimeric G‐proteins are universal eukaryotic signaling elements. In plant guard cells, extracellular calcium (Cao) 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 Caoresponses: 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 Cao. By contrast, stomatal movements ofagb1mutants andagb1/gpa1double‐mutants, as well as those of theagg1agg2 Gγ double‐mutant, were insensitive to Cao. 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 Cao, 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 Caoinduced InsP3 production in Col but not inagb1. In sum, G‐protein signaling viaAGB1/AGG1/AGG2 is essential for Cao‐regulation of stomatal apertures, and stomatal movements in response to Caoapparently require Ca2+‐induced Ca2+release that is likely dependent on Gβγ interaction withPLCs leading to InsP3 production.
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Orchestrating rapid long‐distance signaling in plants with Ca 2+ , ROS and electrical signals
Summary 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.
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- PAR ID:
- 10041483
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- The Plant Journal
- Volume:
- 90
- Issue:
- 4
- ISSN:
- 0960-7412
- Page Range / eLocation ID:
- p. 698-707
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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