Characterization of sexual reproduction in diatoms

Diatoms are a group of diverse unicellular algae that live in both fresh and salt water. Diatoms influence life on earth in several ways. They account for about one fifth of primary production by converting solar energy into organic compounds and produce oxygen. Diatom communities are sensitive to water pollution and are used as tools to monitor environmental conditions. Their cells are covered in shells made of silica which, after cell death, accumulate on the seabed, forming siliceous sediments. The ability of diatoms to store energy in the form of lipids is currently being investigated for future biofuel production. In contrast to the role of diatoms in the ecosystem, comprehension of their potential for biotechnology and an extensive description of morphological diversity, their biology and life cycle regulation are hardly understood at a molecular level. A key feature of the diatoms haplo-diploid life cycle is a unique strategy to switch between reduction of cell size during somatic divisions and its restitution during sexual reproduction. I will use a novel diatom model species Seminavis robusta to perform the first analysis of diatom reproduction at the molecular and cellular level. The proposed project will be centred on identification and characterization of the core cell cycle machinery driving progression through sexual reproduction. Particularly I will focus on cyclins, proteins that associate with cyclin-dependent kinases and are essential for cell cycle progression in all eukaryotes. I will start by cytogenetic analysis of the distinct stages of sexual reproduction in order to get a better understanding of the dynamics of this process and establish cytological hallmarks. Then I will use transcriptional data to select those cyclins that are highly specifically expressed at the moment of mating and formation of zygotes, auxospores and/or initial cells. For each of these cyclins I will verify the specificity of expression and perform initial characterization. Subsequently I will adapt a tandem affinity purification procedure to identify protein complexes in S. robusta. This method will be applied to characterize protein complexes associated with cyclins for which sexual reproduction-specific expression was confirmed. Finally, the most interesting interacting proteins will be selected for characterization in more details. I expect this project to provide substantial insight into key events of cell cycle regulation driving the progression through sexual reproduction. This will allow understanding the molecular pathways directing the fascinating diatom life cycle and the differences to that of other eukaryotes, a pre-condition to improve the application of diatoms as biosensors and energy producers.

Diatoms are agroup of very diverse microscopic algae that live in both fresh and salt waters. Diatoms influence life on the Earth in several ways. They account for about one fifth of Earths primary production, the conversion of solar energy into the synthesis of organic compounds and production of oxygen. Diatom communities are sensitive to water pollution and are used as a tool for monitoring environmental conditions. Their cells are covered in a shell made of silica which, after cell death, accumulates on the seabed forming a layer of siliceous sediments. The ability of diatoms to store energy in the form of lipids is currently being investigated for future biofuel production.As diatoms form acore of the Earths ecosystem and may prove useful for biotechnology, there is aneed for understanding their biology and life cycle regulation at a molecular level. This will be useful both for predicting their responses to a changing environment and utilizing their potential in biotechnology. In my project I worked with diatom Seminavis robusta that shows characteristics typical for other diatom species of the same type such as size reduction during mitotic cell divisions, dependence of sexual reproduction capability on cell size and presence of 2 mating types (sexes): MT- and MT+. But in contrast to other diatom species routinely used for research, this specie can be easily crossed in the laboratory. I aimed to understand how is the mating type (or sex) determined at genetic and molecular level. In my work I used a combination of molecular biology and bioinformatic techniques to get the DNA sequence of the S. robusta sex-determining piece of genome. My results have shown that there are two alleles of the mating locus; one present in both MT+ and MT- strains and one specific for MT+ strain. The mating locus in S. robusta spans tens of kilobases and encodes 21 genes. In future work these genes will be functionally characterized and we aim to find which of them are directly involved in specifying the mating type. Identification of the key gene regulating mating type in diatoms is an important step to facilitate molecular and genetic research on diatoms. It allows easier breeding and speeds up genetic research techniques, both important for the use of diatoms in biotechnology and for a further research of diatom biology.