Distinct Signaling Pathways from the Circadian Clock Participate in Regulation of Rhythmic Conidiospore Development in Neurospora crassa

Nov 29, 2002Eukaryotic cell

Separate circadian clock signals help control daily spore development in Neurospora crassa

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Abstract

The endogenous circadian clock regulates daily rhythms in gene expression related to asexual spore development in Neurospora crassa.

Conidiation can be induced by various environmental signals or may occur rhythmically under constant conditions due to the circadian clock.
The rhythmic expression of the fl gene is dependent on the presence of the ACON-2 protein.
Clock regulation of the eas (ccg-2) gene remains unaffected in an fl mutant strain.
The expression of ccg-1 is rhythmic in an acon-2 mutant strain, indicating independent regulatory pathways.
These findings suggest that the circadian clock and environmental cues operate through distinct mechanisms to control gene expression related to conidiation.

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Several different environmental signals can induce asexual spore development (conidiation) and expression of developmentally regulated genes in Neurospora crassa. However, under constant conditions, where no environmental cues for conidiation are present, the endogenous circadian clock in N. crassa promotes daily rhythms in expression of known developmental genes and of conidiation. We anticipated that the same pathway of gene regulation would be followed during clock-controlled conidiation and environmental induction of conidiation and that the circadian clock would need only to control the initial developmental switch. Previous experiments showed that high-level developmental induction of the clock-controlled genes eas (ccg-2) and ccg-1 requires the developmental regulatory proteins FL and ACON-2, respectively, and normal developmental induction of fl mRNA expression requires ACON-2. We demonstrate that the circadian clock regulates rhythmic fl gene expression and that fl rhythmicity requires ACON-2. However, we find that clock regulation of eas (ccg-2) is normal in an fl mutant strain and ccg-1 expression is rhythmic in an acon-2 mutant strain. Together, these data point to the endogenous clock and the environment following separate pathways to regulate conidiation-specific gene expression.

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Distinct Signaling Pathways from the Circadian Clock Participate in Regulation of Rhythmic Conidiospore Development in Neurospora crassa

Abstract

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