Åsa Strand - Plastid-to-Nucleus Signalling Pathways

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The aim of our research is to dissect and elucidate the signalling pathways between the chloroplast and the nucleus that regulate the expression of nuclear genes encoding chloroplastic proteins. We use an integrative approach with a combination of genetics, molecular biology, cell biology and biochemistry to understand the language of the chloroplasts.
Strand_Asa_portrait

The function of the eukaryotic cell depends on the regulated and reciprocal interaction between its different compartments. This includes not only the exchange of metabolic intermediates and energy equivalents, but also information. The presence of genes encoding organellar proteins in different cellular compartments necessitates a tight coordination of expression from the different genomes. The photosynthetic apparatus is composed of proteins encoded by genes from both the nucleus and the chloroplast and the expression of these genes is influenced by developmental and environmental cues. In the photosynthetic electron transport complexes of the thylakoid membrane, the core subunits are encoded by the plastidic genome and the peripheral subunits are encoded by the nuclear genome. In the stroma, the large subunit of RUBISCO is encoded by the plastid, whereas the small subunit is nuclear encoded. To ensure that all these photosynthetic complexes are assembled stoichiometrically, and to enable their rapid reorganization in response to a changing environment, the activities of the nuclear and chloroplast genomes must be closely coordinated through intracellular signalling.


Model of retrograde signalling between the chloroplast and the nucleus. The organelles produce multiple signals at different times of their development, and in response to changes in the environment, that orchestrate major changes in nuclear gene expression.	We use Arabidopsis thaliana as a model to understand the role of retrograde communication during plant stress responses

TEMs of Arabidopsis mesophyll cells showing the chloroplast structures

The necessity of a tight coordination of expression by the different genomes has led to the evolution of mechanisms to coordinate nuclear and organellar gene expression. These include both anterograde and retrograde controls. Anterograde mechanisms (nucleus-to-organelle) coordinate gene expression in the plastid, with cellular and environmental cues that are perceived and choreographed by proteins encoded in the nucleus. This type of traffic includes proteins that regulate the transcription and translation of organellar genes. Retrograde (organelle-to-nucleus) signalling, on the other hand, coordinates the expression of nuclear genes encoding organellar proteins with the metabolic and developmental state of the plastid and mitochondria through signals emitted from the organelles that regulate nuclear gene expression. It is now clear that several different plastid processes produce these signals and that plastid-to-nucleus communication appears to be of particular importance durng plant stress responses. The plastid signals identified so far can be linked to specific stress conditions, such as: 1) changes of the redox state of the chloroplast, 2) accumula- tion of reactive oxygen species and 3) perturbed flux through tetrapyrrole biosynthesis. The photosynthetic reactions housed in the chloroplasts are extremely sensitive to stress. The chloroplasts therefore act as sensors of environmental changes and complex networks of plastid signals coordinate cellular activities and assist the cell during plant stress responses. Our work suggests that information from both cytosolic and plastid signalling networks must be integrated for the plant cell to respond optimally to environmental stress. In my research group we are taking an integrative approach, using a combination of modern plant genetics, molecular biology, cell biology and biochemistry, to develop a comprehensive model for the plastid-to-nucleus signalling pathways during plant stress response.

Svensk sammanfattning

Key publications

Piñas Fernández A and Strand Å (2008) Retrograde signaling and plant stress: plastid signals initiate cellular stress response. Curr. Opin. Plant Biol., 11:509-513

Ankele E, Pesquet E, Kindgren P and Strand Å (2007) In vivo visualization of Mg-ProtoporphyrinIX, a coordinator of photosynthetic gene expression in the nucleus and the chloroplast. Plant Cell, 19, 1964-1979.

Kleine T, Kindgren P, Benedict C, Hendricksen L and Strand Å (2007) Genome wide gene expression analysis reveals a critical role for CRYPTOCHROME1 in the response of Arabidopsis to high irradiance. Plant Physiol., 144, 1391-1406.

Strand Å (2004). Plastid-to-nucleus signalling. Curr. Opin. Plant Biol., 7(6):621-625

Strand Å, Asami T, Alonso J, Ecker JR, and Chory J (2003) Chloroplast to nucleus communication triggered by accumulation of Mg-protoporphyrinIX. Nature, 421, 79-83.

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May 2013

Sunday, May 26, 2013
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