Calcium (Ca 2+ ) signals initiate egg activation across the animal kingdom and in at least some plants. These signals are crucial for the success of development and, in the case of mammals, health of the offspring. The mechanisms associated with fertilization that trigger these signals and the molecules that regulate their characteristic patterns vary widely. With few exceptions, a major contributor to fertilization-induced elevation in cytoplasmic Ca 2+ is release from endoplasmic reticulum stores through the IP3 receptor. In some cases, Ca 2+ influx from the extracellular space and/or release from alternative intracellular stores contribute to the rise in cytoplasmic Ca 2+ . Following the Ca 2+ rise, the reuptake of Ca 2+ into intracellular stores or efflux of Ca 2+ out of the egg drive the return of cytoplasmic Ca 2+ back to baseline levels. The molecular mediators of these Ca 2+ fluxes in different organisms include Ca 2+ release channels, uptake channels, exchangers and pumps. The functions of these mediators are regulated by their particular activating mechanisms but also by alterations in their expression and spatial organization. We discuss here the molecular basis for modulation of Ca 2+ signalling at fertilization, highlighting differences across several animal phyla, and we mention key areas where questions remain.

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This study provides a comprehensive study of the small GTPase superfamily in several plant species. The genetic program associated to root nodule symbiosis includes small GTPases to fulfill specific functions during infection and formation of the symbiosomes. These GTPases seems to have been recruited from members that were already present in common ancestors with plants as distant as monocots since we failed to detect asymmetric evolution in any of the subfamily trees. Expression analyses identified a number of legume members that can have undergone neo- or sub-functionalization associated to the spatio-temporal transcriptional control during the onset of the symbiotic interaction.