Diatoms shed light on cell cycle mechanisms

15 March 2013

A strict regulation of the cell cycle is of pivotal importance for the growth and development of all eukaryotes. In photosynthetic organisms cell division is tightly regulated by light. Although the light-dependency of the cell cycle has been well characterized, little is known about the specific signaling mechanisms that connect light to cell cycle progression. Marie Huysman from the group of Lieven Deveylder at the VIB Department of Plant Systems Biology, UGent, and the group of Wim Vyverman at the Biology Department of UGent studied how light can regulate the onset of the cell cycle. Using diatoms they were able to demonstrate that the blue-light sensor AUREOCHROME1a functions together with the bZIP10 transcription factor to activate the transcription of dsCYC2, a key regulator of the cell cycle.

Why did you choose to work on diatoms and what are diatoms actually?
Diatoms are unicellular algae and, although they are photosynthetic, they cannot be considered miniature, single-celled plants. They belong to a completely separate evolutionary lineage and are very intriguing organisms since they evolved from sequential endosymbioses involving various groups of prokaryotic and eukaryotic organisms (bacteria, cyanobacteria, red and probably also green algae). Diatoms possess what is called a chimeric genome (a combination of two different types of organisms).

Being part of a totally different evolutionary clade, work on diatoms can give us insight into how cell cycle mechanisms evolved during evolution. Besides that, unicellular organisms are much easier to work with. Phaeodactylum, for example, the diatom species that we work with, is very easy to cultivate and can be stably, genetically transformed in only six weeks.

Diatoms are also of major economic importance. They have applications in aquaculture as food for mollusk larvae and shrimp, in the production of a plethora of metabolites and even in biodiesel production. So increasing our understanding of the molecular mechanisms that control the diatom life cycle will help optimize diatom cultivation.

It was already known that light drives the expression of various cell cycle genes. Which new insights do we have now thanks to your work?
Despite the fact that light plays a key role in the growth of photosynthetic organisms, little is known about the cellular signaling mechanisms that connect light perception with the activation of the cell cycle machinery. In this work, we discovered a part of the upstream signaling cascade that leads to the rapid blue-light-dependent transcription of the cell cycle regulator dsCYC2. Using a yeast-one-hybrid protein-DNA interaction screening we found two bZIP transcription factors that bind the dsCYC2 promoter region. Activation assays demonstrated that both bZIP proteins work together to activate the dsCYC2 promoter. Most interestingly, one of these bZIP proteins belongs to the Aureochrome family of blue-light photoreceptors, suggesting that blue light may directly regulate dsCYC2 transcription through the activation of this photoreceptor.

How did you find the collaboration with the Protistology and Aquatic Ecology Department of
Ghent University?

From a practical viewpoint, commuting between two labs was not the easiest way of conducting experiments, since part of the work was done at one lab and then continued at the other. However, I had the opportunity to work with people from different scientific backgrounds. While the PSB Department has long-standing expertise in cell cycle research, the Protistology and Aquatic Ecology Department is an expert in diatom ecophysiology and basic diatom cell biology. Joining forces led to a very enriching experience for all of us.

Marie Huysman et al.
The Plant Cell 2013

Back (left to right): Michiel Matthijs, Lieven De Veylder, Wim Vyverman

Front (left to right): Rudy Vanderhaeghen, Hilden Van den Daele, Marie Huysman

©VIB, 2013

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