Li S, Motavaze K, Kafes E, Suntharalingam S, Lakin-Thomas P. A new mutation affecting FRQ-less rhythms in the circadian system of Neurospora crassa.
PLoS Genet 2011;
7:e1002151. [PMID:
21731506 PMCID:
PMC3121751 DOI:
10.1371/journal.pgen.1002151]
[Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2010] [Accepted: 05/09/2011] [Indexed: 11/23/2022] Open
Abstract
We are using the fungus Neurospora crassa as a model organism to study the circadian system of eukaryotes. Although the FRQ/WCC feedback loop is said to be central to the circadian system in Neurospora, rhythms can still be seen under many conditions in FRQ-less (frq knockout) strains. To try to identify components of the FRQ-less oscillator (FLO), we carried out a mutagenesis screen in a FRQ-less strain and selected colonies with altered conidiation (spore-formation) rhythms. A mutation we named UV90 affects rhythmicity in both FRQ-less and FRQ-sufficient strains. The UV90 mutation affects FRQ-less rhythms in two conditions: the free-running long-period rhythm in choline-depleted chol-1 strains becomes arrhythmic, and the heat-entrained rhythm in the frq10 knockout is severely altered. In a FRQ-sufficient background, the UV90 mutation causes damping of the free-running conidiation rhythm, reduction of the amplitude of the FRQ protein rhythm, and increased phase-resetting responses to both light and heat pulses, consistent with a decreased amplitude of the circadian oscillator. The UV90 mutation also has small but significant effects on the period of the conidiation rhythm and on growth rate. The wild-type UV90 gene product appears to be required for a functional FLO and for sustained, high-amplitude rhythms in FRQ-sufficient conditions. The UV90 gene product may therefore be a good candidate for a component of the FRQ-less oscillator. These results support a model of the Neurospora circadian system in which the FRQ/WCC feedback loop mutually interacts with a single FLO in an integrated circadian system.
All eukaryotes (including humans), and some bacteria, have evolved internal biological clocks that control activity and physiology in a daily (circadian) cycle. The molecular oscillators that drive these circadian rhythms are said to depend on rhythmic expression and feedback regulation of a small set of “clock genes.” However, there is increasing evidence that there is more to the story than these well-studied feedback loops. In the fungus Neurospora crassa, rhythms can still be seen in mutants that are missing one of the clock genes, frq. There is currently a controversy as to whether there are many different frq-less oscillators and whether they interact with the frq clock. To identify the molecular mechanism that drives these frq-less rhythms, we started with a frq-less strain and mutagenized it to look for genes that affect the frq-less rhythms. We found a new mutation that not only disrupted two frq-less rhythms but also affected the rhythm when the frq gene is present. Our results suggest there is only one frq-less oscillator, and it interacts with the frq clock. Our new mutation may identify a gene that is critical to both oscillators. We suggest that a similar clock architecture may be common to all organisms.
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