Light and developmental regulation of the gene con-10 of Neurospora crassa

The gene con-10 of Neurospora crassa is expressed preferentially during conidiation and following illumination of vegetative mycelia with blue light. In this study we have examined the segmental locations of the genetic elements associated with con-10 that are responsible for light and developmental expression. A translational fusion was prepared between the initial segment of con-10 and Escherichia coli lacZ. Deletions were then introduced into the con-10 upstream region associated with this translational fusion. Each construct was integrated at the his-3 locus of N. crassa by transformation and homologous recombination. Photoinduction of mycelia containing the translational fusion with the intact upstream region revealed a two phase stimulus-response curve. Exposure to light for as little as 5 sec induced a transcriptional response. Following this initial induction, a period of 15 min in the dark or light was required for appearance of a second phase response. Only a brief light treatment was necessary for induction of the second phase response. Deletions within the upstream region altered normal light and developmental expression of constructs containing the con-10-lacZ translational fusion. The deleted segments appear to contain a mycelial repression site, two conidiation activation sites, and two dark repression sites. A repeated 17-bp sequence acted as a transcriptional enhancer. One copy of this enhancer is in the upstream region. The second copy, with the opposite orientation, is located in the first con-10 intron. The enhancer was required for proper mycelial and conidial expression of the con-10-lacZ fusion. The initial 10 bp of this enhancer sequence were sufficient to restore conidial expression to a deletion construct lacking both copies of the 17-bp repeat. Proteins were detected in extracts of mycelia and conidia that specifically bound to the enhancer sequence in vitro. Our findings suggest that conidiation-specific and mycelial-specific expression of con-10 requires the action of several factors acting independently and/or in concert at distinct sites located in the regulatory regions for con-10.