Photoreceptor cells, mutant

Bryant There are no mutants in Cbl but it has been tested in an ectopic expression assay, and if it is expressed in the eye disc it interferes with photoreceptor cell development (Meisner et al 1997). 

Among the many sensory reactions Phycomyces displays, the study of the photoreceptor and adaptation deserves maximal attention, since Phycomyces shares these two attributes with a variety of other blue light sensitive organisms. Action-spectroscopy indicates a flavin as the photoreceptor of Phycomyces. /3-carotene was positively ruled out as a possible receptor, since mutants with no trace amounts of )3-carotene are phototropical normal. The photoreceptor has not yet been isolated. As in other systems the difficulty consists in distinguishing the flavin photoreceptor from the bulk flavoproteins in the cell. One therefore needs unambiguous criteria for the identification of the photoreceptor. The most promising approach for an isolation would be a photoreceptor mutant and we described the properties those mutants should have. Until now there is no firm evidence that the photomutants, madA or madB are defective in the photoreceptor. 

PCR with primers for the two related genes indicated that both PAC a and PAC P were expressed in a number of phototaxis mutant strains, indicating that these are not primary photoreceptor mutants, but downstream mutants (unpublished data). None of the two proteins was detected in Astasia a nonphotosynthetic relative of Euj kna which lacks the PAB and consequently does not show photo taxis. Polyclonal antibodies were raised against these two proteins subunits and found to bind at the site of the PAB in the cell, indicating that these represent the photoreceptor. 

Boylan, M., Douglas, N., and Quail, P.H., Dominant negative suppression of Arabidopsis photoresponses by mutant phytochrome A sequences identifies spatially discrete regulatory domains in the photoreceptor. Plant Cell, 6, 449,1994. 

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