Date: 15th October 2017
Title: Chloroplast development, a tale of two genomes
Location: Viikki B building, seminar room 6, Latokartanonkaari 7-9
Host: Jaakko Kangasjärvi
Abstract: The establishment of photosynthesis through chloroplast development is an intricate process involving several cellular compartments and the progression can be divided into 3 distinct phases. First, chloroplast development is dependent on light and the initial light signal triggers activation of the photoreceptors, initiating large changes in nuclear transcription. Using a mathematical model, validated in vivo, we established a direct link between light input via PHYB-PIF3 and the initiation of chloroplast development. The light activated form of PHYB degrades PIF3, which represses the nuclear-encoded components of the plastid transcriptional machinery required for transcription of the plastid-encoded photosynthesis genes. Secondly, expression of the plastid-encoded photosynthesis genes needs to be initiated and this induction depends upon the assembly of the nuclear-encoded components required for the activity of PEP. Additionally, activation of PEP also includes a redox-controlled mechanism that influences plastid gene expression. We have characterized PLASTD REDOX INSENSITIVE2 (PRIN2), a redox-regulated protein required for full PEP-driven transcription. PRIN2 dimers can be reduced into the active monomeric form by thioredoxins (TRXs) through reduction of a disulfide bond. Third, once photosynthetic gene expression is established in the plastids by the PEP complex, a positive retrograde signal generates full expression of the nucleus-encoded photosynthesis genes. Thus, we conclude that establishment of photosynthesis is dependent on a closed regulatory loop where the plastidic and nuclear genomes strictly control the transcriptional rates of eachs other.
After completing her PhD in Umeå, Åsa moved to the Salk Institute, USA as an EMBO post-doctoral fellow. She later returned to Umeå where she now holds the position of Professor in Plant Cell and Molecular Biology. Her research interests are signals involved in the recovery of energy homeostasis with the emphasis on organelle-to-nucleus communication. Her group uses an integrative approach with a combination of genetics, molecular biology, cell biology and biochemistry to understand the language of the chloroplasts and mitochondria.