Written by Tony Miller on July 13, 2017
A fundamental property of all cellular organisms is that they respond to their environment. As sessile organisms, many plants endure a wide range of environmental conditions, and adverse stimuli such as pathogen attack, wounding, anoxia and cold trigger the appropriate physiological response initally through a calcium signal.
How are these calcium signals generated? Biochemical and electrophysiological research over the last 15 years has resulted in the characterisation of many calcium-permeable channels in plants that serve to admit calcium into the cytosol. However, detailed description of the physiological roles of these channels has been hampered by lack of information on the identity of the genes that encoded the channels.
Recent developments in the use of genetically-encoded calcium indicators (GECIs) is allowing us to measure calcium signals in real time in vivo, and these offer a real opportunity to study these signals at a much better resolution than ever before.
An Arabidopsis root expressing a GECI (YC3.6) shows a large calcium response to ATP application.
TWO PORE CHANNEL 1
In 2005, we discovered that the Two Pore Channel 1 (TPC1) gene of Arabidopsis encodes the calcium-permeable Slow Vacuolar channel at the vacuolar membrane of plants.
Topographical model of the TPC1 channel
(Peiter et al, 2005)
Bright field (upper panels) and fluorescence images (lower panels) of TPC1–GFP-transformed protoplasts (A) & vacuoles (B) isolated after bursting show TPC1-GFP localised to the vacuolar membrane (Peiter et al, 2005)
We were able to ascribe physiological roles to this channel by studying the properties of so-called knock-out mutants. The channel plays a role in the hormonal control of seed germination and in the closure of stomata in leaves.
Current work is aimed at measuring calcium signals in vivo in plants in response to multiple different stresses, and determining the role of TPC1 and other calcium channels in these signals.
This work helped to establish a protocol for measuring Calcium signalling in vivo in Arabidopsis during aphid feeding. This has been published in jove, and features Thomas Vincent (Alumni).
Alumni who have worked on the project:
Vincent, T.R., Canham, J., Toyota, M., Avramova, M., Mugford, S.T., Gilroy, S., Miller, A.T., Hogenhout, S., Sanders, D. (2017) Real-time In Vivo Recording of Arabidopsis Calcium Signals During Insect Feeding Using a Fluorescent Biosensor: in press.
Vincent, T.R., Avramova, M., Canham, J., Higgins, P., Bilkey, N., Mugford, S.T., Pitino, M., Toyota, M., Gilroy, S., Miller, A.T., Hogenhout, S., Sanders, D. (2017) Interplay of Plasma Membrane and Vacuolar Ion Channels, Together with BAK1, Elicits Rapid Cytosolic Calcium Elevations in Arabidopsis during Aphid Feeding. Plant Cell 29(6)
Sanders, D., Pelloux, J., Brownlee, C., Harper, J.F. (2002) Calcium at the crossroads of signaling. Plant Cell 14: S401-S417.
Peiter, E., Maathuis, F.J.M., Mills, L.N., Knight, H., Pelloux, J., Hetherington, A.M., Sanders, D. (2005) The vacuolar Ca2+-activated channel TPC1 regulates germination and stomatal movement. Nature 434: 404-408.
Dodd, A.N., Kudla, J., Sanders, D. (2010) The language of calcium signalling. Annual Review of Plant Biology, 61: 593-620