The GUN 4 protein plays a regulatory role in tetrapyrrole biosynthesis and chloroplast‐to‐nucleus signalling in C hlamydomonas reinhardtii
The GENOMES UNCOUPLED 4 (GUN4) protein is found only in aerobic photosynthetic organisms. We investigated the role of GUN4 in metabolic activities of the Mg branch of the tetrapyrrole biosynthesis pathway and the plastid signal‐mediated changes of nuclear gene expression in C hlamydomonas reinhardti...
Gespeichert in:
Veröffentlicht in: | The Plant journal : for cell and molecular biology 2014-07, Vol.79 (2), p.285-298 |
---|---|
Hauptverfasser: | , , , , , |
Format: | Artikel |
Sprache: | eng |
Online-Zugang: | Volltext |
Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
Zusammenfassung: | The GENOMES UNCOUPLED 4 (GUN4) protein is found only in aerobic photosynthetic organisms. We investigated the role of GUN4 in metabolic activities of the Mg branch of the tetrapyrrole biosynthesis pathway and the plastid signal‐mediated changes of nuclear gene expression in
C
hlamydomonas reinhardtii
. In light,
gun4
accumulates only 40% of the wild‐type chlorophyll level. Light‐ or dark‐grown
gun4
mutant accumulates high levels of protoporphyrin IX (Proto), and displays increased sensitivity to moderate light intensities. Despite the photooxidative stress,
gun4
fails to downregulate m
RNA
levels of the tetrapyrrole biosynthesis and the photosynthesis‐associated nuclear genes (
PhANG
s). In contrast, upon illumination, the Proto‐accumulating and light‐sensitive
chlD–1
mutant displays the expected downregulation of the same nuclear genes. Although
chlD–1
and the wild type have similar
GUN
4
transcript levels, the
GUN
4 protein in
chlD–1
is hardly detectable. Overexpression of
GUN
4
in
chlD–1
modifies the downregulation of nuclear gene expression, but also increases light tolerance. Therefore, GUN4 is proposed to function in ‘shielding’ Proto, and most likely MgProto, by reducing reactivity with O
2
. Furthermore,
GUN
4 seems to be involved in sensing elevated levels of these photoreactive tetrapyrrole intermediates, and contributing to
1
O
2
‐mediated retrograde signalling, originating from chlorophyll biosynthesis. |
---|---|
ISSN: | 0960-7412 1365-313X |
DOI: | 10.1111/tpj.12560 |