Current understanding of GUN1: a key mediator involved in biogenic retrograde signaling

  • Paolo Pesaresi
  • Chanhong KimEmail author
Review Article


Chloroplast–nucleus communication takes place via processes called anterograde and retrograde signaling pathways. Discovery of the retrograde signaling pathways from the chloroplasts to the nucleus also raised an intriguing proposition that chloroplasts may serve as environmental sensors since multitudes of environmental factors disturb chloroplastic homeostasis. Certain chloroplastic perturbations, mostly impairing transcription/translation, are coupled to the repression of photosynthesis-associated nuclear genes (PhANGs), thus finely coordinating photosynthetic and chloroplastic homeostasis. The unbiased forward genetic screen in Arabidopsis leads to the identification of six independent loci called GENOMES UNCOUPLED (GUN), whose inactivation was found to de-repress the expression of PhANGs under certain conditions promoting retrograde signaling. Of the six GUNs, five encode proteins associated with tetrapyrrole biosynthesis and one, namely GUN1, encodes a member of the pentatricopeptide repeat protein family. Despite the fact that GUN1 plays a role as a central signaling mediator for retrograde communication, the molecular details of GUN1 protein still remain to be elucidated. Here, we recapitulate our current understanding of the GUN1-mediated retrograde signaling pathway and propose a possible mode of action of GUN1 in the chloroplasts together with different aspects of GUN1 protein activity that deserve further investigation.


Retrograde signaling Genomes uncoupled 1 Photosynthesis-associated genes 



We apologize to those authors whose manuscripts are not referred in this short review due to limited space. This study was supported by the 100-Talents Program from the Chinese Academy of Sciences (CAS) and by the National Natural Science Foundation of China (NSFC) Grant 31570264 to C. K.

Compliance with ethical standards

Conflict of interest

We have no conflict of interests to declare.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of BiosciencesUniversity of MilanoMilanItaly
  2. 2.Shanghai Center for Plant Stress Biology and Center of Excellence in Molecular Plant Sciences, Chinese Academy of SciencesShanghaiChina

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