GUN1, a Jack-Of-All-Trades in Chloroplast Protein Homeostasis and Signaling

The gene has been reported to encode a chloroplast-localized pentatricopeptide-repeat protein, which acts to integrate multiple indicators of plastid developmental stage and altered plastid function, as part of chloroplast-to-nucleus retrograde communication. However, the molecular mechanisms underl...

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Bibliographic Details
Published in:Frontiers in plant science 2016-09, Vol.7, p.1427-1427
Main Authors: Colombo, Monica, Tadini, Luca, Peracchio, Carlotta, Ferrari, Roberto, Pesaresi, Paolo
Format: Article
Language:English
Subjects:
Biogenic control
GUN1
nucleoid
Plant Science
Protein homeostasis
retrograde signaling
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Summary:The gene has been reported to encode a chloroplast-localized pentatricopeptide-repeat protein, which acts to integrate multiple indicators of plastid developmental stage and altered plastid function, as part of chloroplast-to-nucleus retrograde communication. However, the molecular mechanisms underlying signal integration by GUN1 have remained elusive, up until the recent identification of a set of GUN1-interacting proteins, by co-immunoprecipitation and mass-spectrometric analyses, as well as protein-protein interaction assays. Here, we review the molecular functions of the different GUN1 partners and propose a major role for GUN1 as coordinator of chloroplast translation, protein import, and protein degradation. This regulatory role is implemented through proteins that, in most cases, are part of multimeric protein complexes and whose precise functions vary depending on their association states. Within this framework, GUN1 may act as a platform to promote specific functions by bringing the interacting enzymes into close proximity with their substrates, or may inhibit processes by sequestering particular pools of specific interactors. Furthermore, the interactions of GUN1 with enzymes of the tetrapyrrole biosynthesis (TPB) pathway support the involvement of tetrapyrroles as signaling molecules in retrograde communication.
ISSN:1664-462X
1664-462X
DOI:10.3389/fpls.2016.01427