Phototactic activity inChlamydomonas'non-phototactic' mutants deficient in Ca2+-dependent control of flagellar dominance or in inner-arm dynein

Abstract

In the mechanism underlying the phototactic behavior of Chlamydomonas, Ca2+ has been thought to control the dominance between the two flagella so as to steer the cell to correct directions. A newly isolated mutant, lsp1, that displays weak phototaxis was found to be defective in this Ca2+-dependent shift in flagellar dominance; in demembranated and reactivated cell models, the trans flagellum (the flagellum farthest from the eyespot) beat more strongly than the other (the cis flagellum) in about half of the cells regardless of the Ca2+ concentration between <10-9 M and 10-6 M, a range over which wild-type cell models display switching of flagellar dominance. This is unexpected because ptx1, another mutant that is also deficient in flagellar dominance control, has been reported to lack phototactic ability. We therefore re-examined ptx1 and another reportedly non-phototactic mutant, ida1, which lacks inner arm dynein subspecies f (also called I1). Both were found to retain reduced phototactic abilities. These results indicate that both Ca2+-dependent flagellar dominance control and inner-arm dynein subspecies f are important for phototaxis, but are not absolutely necessary. Analysis of the flagellar beat frequency in lsp1 cell models showed that both of the flagella beat at the frequency of the cis flagellum in wild type. In addition, lsp1 and ptx1 were found to be deficient in determining the sign of phototactic migration. Hence, the Ca2+-dependent flagellar dominance control detected in demembranated cells might be involved in the determination of the sign of phototaxis. The gene responsible for the lsp1 mutation was identified by phenotype rescue experiments and found to have sequences for phosphorylation.

Coordinated beating of algal flagella is mediated by basal coupling

“…Because BBs nucleate/anchor flagella and function as centrioles during cell division, the DF can also be affected by mutations in BB duplication and segregation (36). This brings us back to the unusual flagellar coordination in ptx1, which is thought to possess two trans-like flagella (64). If BB signaling or connectivity is disrupted or weakened in ptx1, stochastic IP/AP transitions can result when hydrodynamic interactions compete with a reduced intracellular coupling (15).…”

Keeping an eye on I1: I1 dynein as a model for flagellar dynein assembly and regulation

“…In some cases, mutations that affect I1-dynein assembly suppress paralysis in a central pair mutant . Also, I1-dynein assembly mutants exhibit defects in phototaxis-a behavioral response to a light stimulus that requires precise control of flagellar bending indicating I1 is important, although not absolutely required, in this process [King and Dutcher, 1997;Okita et al, 2005]. These phenotypic data demonstrate that I1 dynein is a critical component of a complex system, involving multiple axonemal dyneins, which controls axonemal bending.…”

“…The novel structures linking I1-dynein to the outer arm may be composed of the Oda7 protein [Freshour et al, 2006;Nicastro et al, 2006]. Kamiya et al, 1991;Porter et al, 1992;Okita et al, 2005;Piperno et al, 1990;Brokaw and Kamiya, 1987 Altered waveform, phototaxis Mutations affecting the inner dynein arm system generally are referred to as ida mutants (Kamiya et al, 1991). Exceptions to this system of nomenclature include mutants designated as pf (paralyzed flagella), bop (bypass of paralysis), or mia (modifiers of inner arms); named either prior to the establishment of the ida nomenclature or prior to the recognition that the mutation affected inner arm dyneins.…”

“…Mutations in I1-dynein subunits or mutations that alter I1 phosphorylation result in failure of control of normal axonemal waveform and phototaxis in Chlamydomonas [Brokaw and Kamiya, 1987;King and Dutcher, 1997;Okita et al, 2005]. For example, the mia mutants were isolated in a screen for phototaxis mutations and the mutant axonemes exhibit hyperphosphorylated IC138 [King and Dutcher, 1997].…”

52-1:Invited Paper: OLED Microdisplays Control Cell Behavior through Optogenetics

“…CC125 showed a linear increase in cell density with optical power density and thus exhibits positive phototaxis. As a control, we used the strain CC2894, known to show only weak phototaxis [9]. For this stain, we did not detect a statistically significant change in cell density across the whole range of optical power densities applied.…”