Ankele E, Kindgren P, Pesquet E, Strand Å
In Vivo visualization of Mg-ProtoporphyrinIX, a coordinator of photosynthetic gene expression in the nucleus and the chloroplast
The Plant Cell: 2007 19:1964-1979
Abstract
The photosynthetic apparatus is composed of proteins encoded by genes
from both the nucleus and the chloroplast. To ensure that the
photosynthetic complexes are assembled stoichiometrically and to enable
their rapid reorganization in response to a changing environment, the
plastids emit signals that regulate nuclear gene expression to match
the status of the plastids. One of the plastid signals, the chlorophyll
intermediate Mg-ProtoporphyrinIX (Mg-ProtoIX) accumulates under stress
conditions and acts as a negative regulator of photosynthetic gene
expression. By taking advantage of the photoreactive property of
tetrapyrroles, Mg-ProtoIX could be visualized in the cells using
confocal laser scanning spectroscopy. Our results demonstrate that
Mg-ProtoIX accumulated both in the chloroplast and in the cytosol
during stress conditions. Thus, the signaling metabolite is exported
from the chloroplast, transmitting the plastid signal to the cytosol.
Our results from the Mg-ProtoIX over- and underaccumulating mutants
copper response defect and genome uncoupled5, respectively, demonstrate
that the expression of both nuclear- and plastid-encoded photosynthesis
genes is regulated by the accumulation of Mg-ProtoIX. Thus,
stress-induced accumulation of the signaling metabolite Mg-ProtoIX
coordinates nuclear and plastidic photosynthetic gene expression.
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