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PLANTS INTERACTING WITH OTHER ORGANISMS

The Medicago truncatula DMI1 Protein Modulates Cytosolic Calcium Signaling^1,[W],[OA]

Biology Department, University of York, York YO10 5YW, United Kingdom (E.P., D.S.); John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom (J.S., A.B.H., A.E., G.E.D.O., J.A.D.); Department of Agronomy (M.V., J.-M.A.) and Department of Botany (M.S.O.), University of Wisconsin, Madison, Wisconsin 53706; Department of Plant Pathology, University of California, Davis, California 95616 (B.K.R., D.R.C.); and Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602–4712 (G.F., M.G.H.)

In addition to establishing symbiotic relationships with arbuscular mycorrhizal fungi, legumes also enter into a nitrogen-fixing symbiosis with rhizobial bacteria that results in the formation of root nodules. Several genes involved in the development of both arbuscular mycorrhiza and legume nodulation have been cloned in model legumes. Among them, Medicago truncatula DMI1 (DOESN'T MAKE INFECTIONS1) is required for the generation of nucleus-associated calcium spikes in response to the rhizobial signaling molecule Nod factor. DMI1 encodes a membrane protein with striking similarities to the Methanobacterium thermoautotrophicum potassium channel (MthK). The cytosolic C terminus of DMI1 contains a RCK (regulator of the conductance of K⁺) domain that in MthK acts as a calcium-regulated gating ring controlling the activity of the channel. Here we show that a dmi1 mutant lacking the entire C terminus acts as a dominant-negative allele interfering with the formation of nitrogen-fixing nodules and abolishing the induction of calcium spikes by the G-protein agonist Mastoparan. Using both the full-length DMI1 and this dominant-negative mutant protein we show that DMI1 increases the sensitivity of a sodium- and lithium-hypersensitive yeast (Saccharomyces cerevisiae) mutant toward those ions and that the C-terminal domain plays a central role in regulating this response. We also show that DMI1 greatly reduces the release of calcium from internal stores in yeast, while the dominant-negative allele appears to have the opposite effect. This work suggests that DMI1 is not directly responsible for Nod factor-induced calcium changes, but does have the capacity to regulate calcium channels in both yeast and plants.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jean-Michel Ané (jane{at}wisc.edu).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.097261

^* Corresponding author; e-mail jane{at}wisc.edu.

Received January 31, 2007; accepted July 5, 2007; published July 13, 2007.

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Peter V. Minorsky
Plant Physiol. 2007 145: 1-2. [Full Text]