Ancient signal for nitrogen status sensing in the green lineage: Functional evidence of CDPK repertoire in Ostreococcus tauri

Abstract

Calcium-dependent protein kinases (CDPKs) regulate plant development and many stress signalling pathways through the complex cytosolic [Ca2+] signalling. The genome of Ostreococcus tauri (Ot), a model prasinophyte organism that is on the base of the green lineage, harbours three sequences homologous to those encoding plant CDPKs with the three characteristic conserved domains (protein kinase, autoregulatory/autoinhibitory, and regulatory domain). Phylogenetic and structural analyses revealed that putative OtCDPK proteins are closely related to CDPKs from other Chlorophytes. We functionally characterised the first marine picophytoeukaryote CDPK gene (OtCDPK1) and showed that the expression of the three OtCDPK genes is up-regulated by nitrogen depletion. We conclude that CDPK signalling pathway might have originated early in the green lineage and may play a key role in prasinophytes by sensing macronutrient changes in the marine environment.