CASTOR and POLLUX, two ion channels required for perinuclear calcium-spiking
Zusammenfassung der Projektergebnisse
In this project we have characterised the function and localisation of the CASTOR/POLLUX ion channel family. We have found that a single serine to alanine substitution within the putative selectivity filter (ADSGNHA to ADAGNHA) was apparently associated with a functional improvement of the symbiotic ion channel DMI1 present in the Vicieae and Trifolieae clades, over the CASTOR/POLLUX duo, present in all other AM forming plants. This change was responsible for the conversion of a large conductance channel with a short open-state (CASTOR) into an intermediate conductance channel with an apparently longer open lifetime (DMI1), which is associated with the capacity of DMI1 to act as a more efficient counter ion channel during Ca2+ signaling, and may explain why this Ala residue has been positively selected and maintained in the Vicieae and Trifolieae clades. We obtained evidence that the in vivo substrate of these channels, relevant for their function in symbiosis, is indeed potassium. A mutated DMI1 channel with filter region of a typical K+ channel, DMI1-YGD (filter region: ADAGNHA → ADAGYGD), exhibited a stronger selectivity for K+ in preliminary electrophysiological studies, and was able to complement a symbiotically defective dmi1 mutant. Preliminary evidence suggests that mevalonate, a possible second messenger produced by HMGR1, and interactor of the symbiotic receptor kinase SYMRK, may directly modulate on the DMI1 channel activity. Nuclear pore mutants are hypothetically impaired in proper movement of the channels from the outer to the inner nuclear membrane. By using a bimolecular fluorescence complementation approach we could obtain evidence for the localisation of CASTOR and POLLUX in the inner nuclear membrane. This localization may be critical for a the channels function in symbiotic signalling as suggested by successful rescue assays of nuclear pore mutants.
Projektbezogene Publikationen (Auswahl)
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(2011) One amino acid change in the evolution of the CASTOR/POLLUX/DMI1 ion channel family altered its symbiotic and electrophysiological activity; Botanical Tagung 2011, Berlin, Germany (Poster Prize)
Cosme, A., Binder, A., Venkateshwaran, M., Lu, H., Banba, M., Satyshure, K.A., Charpentier, M., Schleiff, E., Imaizumi-Anraku, H., Ané, J.M., Parniske, M.
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(2012) Recent evolution in the filter region of a plant ion channel changed its conductance and improved functionality, Gordon Conference on "Ion channels", Mount Holyoke College, South Hadley, MA, USA
Cosme, A., Venkateshwaran, M., Lu, H., Banba, M., Satyshure, K.A., Schleiff, E., Imaizumi-Anraku, H., Ané, J.M., Parniske, M.
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(2012). The recent evolution of a symbiotic ion channel in the Legume family altered ion conductance and improved functionality in calcium signaling, Plant Cell, 24: 2528-2545
Venkateshwaran, M., Cosme, A., Han, L., Banba, M., Satyshur, K.A., Schleiff, E., Parniske, M., Imaizumi-Anraku, H., and Ané, J.-M.
