MUTANTS OF NEUROSPORA-CRASSA DEFECTIVE IN REGULATION OF BLUE-LIGHT PERCEPTION

A new selection system was used to isolate mutants deficient in regula tion of blue light perception in Neurospora crassa. This selection sys tem has two possible applications and was used for the isolation of ei ther blind or constitutive mutants. We isolated 17 UV-induced mutants that showed the pleiotropic white collar (wc) phenotype and were compl etely blocked in transduction of the light signal. From the segregatio n pattern in sexual crosses, we tentatively assigned the 17 mutants to either the wc-1 or wc-2 gene. Furthermore, two Neurospora mutants, cc b-1 and ccb-2, were isolated that showed constitutive carotenoid biosy nthesis in the dark. Analysis of these mutants for transcripts of the carotenoid biosynthesis genes al-3 and al-1 revealed no higher steady- state levels in the dark than in the control strain. The mutant ccb-2 showed major differences in mRNA levels only for conidiation and devel opmental genes. The lack of a specific change in mRNA levels in respon se to light, and the mutant phenotype, which seems to reflect a step i n conidiation, indicate a role for the ccb-2 product in a developmenta l process, such as conidiation. In contrast, the mutant ccb-1 showed a threefold overinduction of carotenoid biosynthesis genes in response to light. This effect was not observed for the conidiation genes exami ned. The recessive nature of the ccb-1 mutation, together with its spe cific effect on light induction of the carotenoid biosynthesis genes, indicate that the gene product of ccb-1 acts as a repressor of transcr iption in some light-regulated processes, but not others.