TRP channel responsible for the responses to collision, agitation, and shear in Chlamydomonas.

Abstract

Swimming microorganisms show various responses to mechanical stimuli. Chlamydomonas cells temporarily swim backward on collision with an obstacle. Beat frequency of cilia increases when agitation is applied by voltexing. Cilia are detached on application of shear with a Dounce-type homogenizer. In this study, we show that a knockout mutant of TRP11, a TRP channel of Chlamydomonas, is defective in all these mechanoresponses. To mimic the mechanical stimulus on collision, we caught a single cell on a glass pipette and tapped the anterior cilia-bearing end of the cell with a micro-glass rod while recording the ciliary motility. On tapping the cell, the bending pattern of cilia changed from the forward mode to the reverse mode. The knockout mutant of TRP11 was deficient in showing this response. The response rarely occurred when the speed of the rod was slower than 100 µm/s, which roughly coincides with the swimming velocity. In addition, the bending pattern conversion hardly occurred when the rod stopped moving 1 µm or more apart from the anterior end of the cell. These findings are consistent with the localization of TRP11 in the proximal region of cilia and the idea that the avoiding reaction on collision is brought about by the activation of TRP11 through the deformation of the proximal region of cilia. TRP11 structure predicted by AlphaFold2 shows conservation of the typical TRP channel structure including pre-S1, S1-S4, S4-S5 linker, S5-pore helix-S6, and TRP helix, while bearing long but poorly resolved sequences of extracellular S1-S2 linker and intracellular C-terminal region.