Prof. Nicolas Buchler (Duke) will be visiting on Friday, May 1, and giving a talk on “Redox rhythms couple to the plant circadian clock and the yeast cell cycle”. He will be hosted by Prof. Liz Rhoades.
Abstract: Biological oscillators such as the cell cycle, circadian clocks, and metabolic rhythms are ubiquitous across the domains of life. These biochemical oscillators co-exist in the same cells, often sharing and competing for resources. How do biochemical oscillators with different frequencies co-exist in the same cell? Are there mechanisms and regulatory principles that ensure harmony between oscillators?
Recent studies have shown that in addition to the transcriptional circadian clock, many organisms, including Arabidopsis, have a circadian redox rhythm driven by the organism’s metabolic activities. It has been hypothesized that the redox rhythm is linked to the circadian clock, but the mechanism and the biological significance of this link have only begun to be investigated. I will show that the master immune regulator NPR1 of Arabidopsis is a sensor of the plant’s redox state and regulates transcription of core circadian clock genes even in the absence of pathogen challenge. Surprisingly, acute perturbation in the redox status triggered by the immune signal salicylic acid does not compromise the circadian clock but rather leads to its reinforcement. Mathematical modelling and subsequent experiments show that NPR1 reinforces the circadian clock without changing the period by regulating both the morning and the evening clock genes. This balanced network architecture helps plants gate their immune responses to the morning and minimize costs on growth at night.
In the second half of my talk, I will discuss the coupling of cell division cycle (CDC) and yeast metabolic cycle (YMC) in budding yeast. The YMC consists of alternating periods of buildup and oxidation of storage carbohydrates, such as trehalose and glycogen, and changes in expression of a large fraction of the transcriptome. The CDC couples strongly to this oscillation, with a single pulse of cells entering S phase once per YMC. Different groups have used different lab strains to study YMC-CDC coupling, which have led to disagreement on the fundamental frequency of the YMC and the nature of YMC-CDC coupling. Here, we examined YMC-CDC coupling in different lab strains and wild-isolates across varying chemostat conditions. Our analysis shows that all strains exhibit a linear relationship between YMC and CDC frequencies, that the high oxygen consumption phase can overlap DNA replication in many strains, and that the interval between entry into high oxygen consumption phase and DNA replication is invariant for any given strain across growth conditions. Our data support a model where cell cycle Start is tightly coupled to events surrounding the oxidation of storage carbohydrates and entry into high oxygen consumption phase. The functional role of YMC-CDC coupling may be to ensure that DNA replication and cell division occur only when sufficient cellular energy is available.