Calmodulin regulates a TRP channel (ADF1) and phospholipase C (PLC) to mediate elevation of cytosolic calcium during acidic stress that induces deflagellation in Chlamydomonas.

Calcium has been implicated in the motility, assembly, disassembly, and deflagellation of the eukaryotic flagellum or cilium (exchangeable terms). Calmodulin (CaM) is known to be critical for flagellar motility; however, it is unknown whether and how CaM is involved in other flagella-related activities. We have studied CaM in Chlamydomonas, a widely used organism for ciliary studies. CaM is present in the cell body and the flagellum, with enrichment in the basal body region. Loss of CaM causes shortening of the nucleus basal body connector and impairs flagellar motility and assembly but not flagellar disassembly. Moreover, the cam mutant is defective in pH shock-induced deflagellation. The mutant deflagellates, however, upon mechanical shearing and treatment with mastoparan or detergent undergo permeabilization in the presence of calcium, indicating the cam mutant is defective in elevations of cytosolic calcium induced by pH shock, rather than by the deflagellation machinery. Indeed, the cam mutant fails to produce inositol 1,4,5-trisphosphate. Biochemical and genetic analysis showed that CaM does not directly activate PLC. Furthermore, CaM interacts with ADF1, a transient receptor channel that functions in acid-induced calcium entry. Thus, CaM is a critical regulator of flagellar activities especially those involved in modulating calcium homeostasis during acidic stress.-Wu, Q., Gao, K., Zheng, S., Zhu, X., Liang, Y., Pan, J. Calmodulin regulates a TRP channel (ADF1) and phospholipase C (PLC) to mediate elevation of cytosolic calcium during acidic stress that induces deflagellation in Chlamydomonas.