Abstract
Oscillation of cytosolic Ca2+ (Ca spiking) has been observed in the root hair of legume following by Nod factor application. Genetic and physiological analyses of symbiotic mutants, which show nodulation and mycorrhization defective phenotypes, have provided strong evidences that Ca spiking is an indispensable step leading to nodulation and mycorrhization. Recent studies of these mutants elucidate host genes that are involved in activation or perception of Ca spiking.
We have identified the CASTOR and POLLUX genes, which encode plastid-localized ion channel-like proteins. Considering mutant phenotypes, it would appear that CASTOR and POLLUX lie upstream of Ca spiking and mediate ion-fluxes between plastids and cytosol which are a prerequisite for Ca spiking. DMI3/LjCCaMK have been positioned downstream of Ca spiking and identified as a calcium calmodulin dependent protein kinase. DMI3/LjCCaMK may perceive oscillation of Ca concentration and phosphorylate downstream targets, which are involved in nodulation or mycorrhization related signal transduction cascades
