Plant Symbiont Biology
Venkateshwaran, Muthusubramanian , Riely, Brendan K. , Peiter, Edgar , Sun, Jongho , Heckmann, Anne B. , Lougnon, Geraldine , Edwards, Anne , Otegui, Marisa , Freshour, Glenn , Hahn, Michael G. , Sanders, Dale , Oldroyd, Giles E. D. , Downie, Allan J. , Cook, Douglas R. , Ane, Jean-Michel .
Medicago truncatula DMI1 localizes to the nuclear envelope and regulates Nod factor-induced calcium spiking.
In addition to establishing symbiotic relationships with arbuscular mycorrhizal fungi, legumes also enter into a nitrogen-fixing symbiosis with rhizobial bacteria that result in the formation of root nodules. Several genes required for the development of these symbioses have been cloned in model legumes. Among them, the M. truncatula DMI1 protein shares strong homologies with prokaryotic ion channels such as MthK. Two DMI1 homologs in L. japonicus, named CASTOR and POLLUX, have been localized in plastids. However our studies indicate that DMI1 is localized on the nuclear envelope. The N-terminal soluble domain of DMI1 is sufficient but not necessary to target the protein to nuclear envelope. This domain is also required for the functionality of DMI1. The soluble C-terminus of DMI1 contains an RCK (regulator of the conductance of K+) domain which in MthK acts as a calcium-regulated gating ring controlling the activity of the channel. 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 mutant towards 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.
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1 - University of Wisconsin-Madison, Agronomy, 219 Moore Hall, 1575 Linden Drive, Madison, WI, 53726, USA
2 - University of California Davis, Plant Pathology
3 - University of York, Biology
4 - John Innes Centre, UK, Molecular Microbiology
5 - University of Wisconsin Madison, Agronomy
6 - University of Wisconsin-Madison, Botany
7 - Complex Carbohydrate Research Center, University of Georgia, Plant Biology
8 - John Innes Centre, UK, Disease and Stress Biology
9 - University of California, Davis, Plant Pathology
10 - University of Wisconsin-Madison, Agronomy
Presentation Type: ASPB Minisymposium
Location: Continental C/Hilton
Date: Monday, July 9th, 2007
Time: 11:55 AM