The mycorrhizal symbiosis has been also associated with increased resistance to pathogen infection and tolerance to abiotic stress in several plant species. The main benefit for the plant is improved uptake of water and mineral nutrients from the soil, particularly phosphate, in exchange for photosynthetically fixed carbon. Most vascular flowering plants have the ability to establish symbiotic associations with arbuscular mycorrhizal (AM) fungi. These findings provide a better understanding of the signaling mechanisms operating during the AM symbiosis and will greatly facilitate their molecular dissection. The OsCPK18 gene might be considered as a marker for the presymbiotic phase of the symbiotic process. The rapid activation of OsCPK18 expression in response to AM inoculation, its expression being also induced by fungal-secreted signals, together with the observed plasma membrane localization of OsCPK18, points to a role for OsCPK18 in perception of the AM fungus. We also show that the myristoylation site of the OsCPK18 N-terminus is required for plasma membrane targeting. Moreover, a plasma membrane localization of OsCPK18 was observed by transient expression assays of green fluorescent protein-tagged OsCPK18 in onion epidermal cells. intraradices-inoculated rice roots, suggesting a preferential role of this gene in the root cortex. Laser microdissection revealed expression of OsCPK18 in cortical cells, and not in epidermal cells of G. OsCPK18 and OsCPK4 gene expression was also up-regulated by fungal-produced diffusible molecules. Among them, OsCPK18 and OsCPK4, were found to be transcriptionally activated in response to inoculation with the AM fungus Glomus intraradices. The expression of seventeen Calcium-dependent Protein Kinase (CPK) genes representative of the four distinct phylogenetic groups of rice CPKs was monitored during the presymbiotic phase of the AM symbiosis. Even though calcium transients are known to occur in host cells during the AM symbiosis, the decoding of the calcium signal and the molecular events downstream are only poorly understood.

In plants, calcium plays a key role as second messenger during developmental processes and responses to environmental stimuli. Then, the establishment of the arbuscular mycorrhizal (AM) symbiosis requires the fine tuning of host gene expression for recognition and accommodation of the fungal symbiont. This association provides the arbuscular mycorrhizal fungus with sugars while the fungus improves the uptake of water and mineral nutrients in the host plant. The arbuscular mycorrhizal (AM) symbiosis consists of a mutualistic relationship between soil fungi and roots of most plant species.

Dim3 expression not recognized