A rice calcium-dependent protein kinase is expressed in cortical root cells during the presymbiotic phase of the arbuscular mycorrhizal symbiosis

Abstract

BackgroundThe arbuscular mycorrhizal (AM) symbiosis consists of a mutualistic relationship between soil fungi and roots of most plant species. This association provides the arbuscular mycorrhizal fungus with sugars while the fungus improves the uptake of water and mineral nutrients in the host plant. 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. In plants, calcium plays a key role as second messenger during developmental processes and responses to environmental stimuli. 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.ResultsThe 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. Among them, OsCPK18 and OsCPK4, were found to be transcriptionally activated in response to inoculation with the AM fungus Glomus intraradices. OsCPK18 and OsCPK4 gene expression was also up-regulated by fungal-produced diffusible molecules. Laser microdissection revealed expression of OsCPK18 in cortical cells, and not in epidermal cells of G. intraradices-inoculated rice roots, suggesting a preferential role of this gene in the root cortex. Moreover, a plasma membrane localization of OsCPK18 was observed by transient expression assays of green fluorescent protein-tagged OsCPK18 in onion epidermal cells. We also show that the myristoylation site of the OsCPK18 N-terminus is required for plasma membrane targeting.ConclusionThe 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. The OsCPK18 gene might be considered as a marker for the presymbiotic phase of the symbiotic process. These findings provide a better understanding of the signaling mechanisms operating during the AM symbiosis and will greatly facilitate their molecular dissection.

Direct Phosphorylation and Activation of a Mitogen-Activated Protein Kinase by a Calcium-Dependent Protein Kinase in Rice

“…Transient expression of green fluorescent protein (GFP)-tagged MPK5 and CPK18 in onion (Allium cepa) epidermal cells and rice protoplasts showed that MPK5 was localized in the nucleus and cytoplasm, whereas CPK18 was predominantly associated with the plasma membrane ( Figure 2B). These observations are in agreement with previously reported locations of CPK18 (Campos-Soriano et al, 2011) and MPK5 (Singh et al, 2012). When MPK5-nYFP (the N-terminal half of YFP [yellow fluorescent protein]) and CPK18-cYFP (the C-terminal half of YFP) were coexpressed in onion cells or rice protoplasts, the complemented YFP signal was observed along the plasma membrane, as was CPK18-GFP ( Figure 2B).…”

The Nitrate Transporter (NRT) Gene Family in Poplar

“…In addition to ROOTMOTIFTAPOX1 we found further CREs related to tissue-specific expression such as NODCON1G/NODCON2G [77], POLLEN1LELAT52 [78], and TAAAGSTKST1 [79]. However, we could not find a direct relationship between the enrichment of these motifs and the tissue-specific expression of their corresponding PtNRT genes.…”

Simultaneous Transcriptome Analysis of Sorghum and Bipolaris sorghicola by Using RNA-seq in Combination with De Novo Transcriptome Assembly

“…One of the CDPKs, Sb04g002220, is the putative ortholog of OsCPK4 in rice (Figure S1). OsCPK4 is transcriptionally activated in response to inoculation with the arbuscular mycorrhizal fungus Glomus intraradices [62]. These ortholog data suggest that Sb04g002220 is involved in responses to both pathogenic and symbiotic fungi.…”