Genome wide identification and biochemical characterization of Calcineurin B-like calcium sensor proteins in Chlamydomonas reinhardtii.

Calcium (Ca2+) signalling is involved in the regulation of diverse biological functions through association with several proteins that enable them to respond to abiotic and biotic stresses. Though Ca2+-dependent signalling has been implicated in the regulation of several physiological processes in Chlamydomonas reinhardtii, Ca2+ sensor proteins are not characterized completely. Chlamydomonas reinhardtii has diverged from land plants lineage, but shares many common genes with animals, particularly those encoding proteins of the eukaryotic flagellum (or cilium) along with the basal body. Calcineurin, a Ca2+/calmodulin-dependent protein phosphatase, is an important effector of Ca2+ signalling in animals, while calcineurin B-like proteins (CBLs) play an important role in Ca2+ sensing and signalling in plants. The present study led to the identification of 13 novel CBL-like Ca2+ sensors in Chlamydomonas reinhardtii genome. One of the archetypical genes of the newly identified candidate, CrCBL-like1 was characterized. The ability of CrCBL-like1 protein to sense as well as bind Ca2+ were validated using two-step Ca2+-binding kinetics. The CrCBL-like1 protein localized around plasma membrane, basal bodies and in flagella, and interacted with voltage gated Ca2+ channel protein (VGCC) present abundantly in the flagella, indicating its involvement in the regulation of the Ca2+ concentration for flagellar movement. The CrCBL-like1 transcript and protein expression was also found to respond to abiotic stresses, suggesting its involvement in diverse physiological processes. Thus, the present study identifies novel Ca2+ sensors and key players involved in Ca2+signalling in Chlamydomonas reinhardtii and help to understand the evolution of Ca2+ mediated signalling in other eukaryotes.