GUN4, a Regulator of Chlorophyll Synthesis and Intracellular Signaling

  title={GUN4, a Regulator of Chlorophyll Synthesis and Intracellular Signaling},
  author={Robert M. Larkin and Jos{\'e} M. Alonso and Joseph R. Ecker and Joanne Chory},
  pages={902 - 906}
Nuclear genes control plastid differentiation in response to developmental signals, environmental signals, and retrograde signals from plastids themselves. In return, plastids emit signals that are essential for proper expression of many nuclear photosynthetic genes. Accumulation of magnesium-protoporphyrin IX (Mg-Proto), an intermediate in chlorophyll biosynthesis, is a plastid signal that represses nuclear transcription through a signaling pathway that, inArabidopsis, requires the GUN4 gene… 
Pathways of intracellular communication: tetrapyrroles and plastid-to-nucleus signaling.
The gun (genomes uncoupled) mutants of Arabidopsis have been used to demonstrate that Mg-protoporphyrin (Mg-Proto) acts as a plastid signal to repress the transcription of nuclear photosynthesis genes.
Signals from Chloroplasts Converge to Regulate Nuclear Gene Expression
This work proposes a model in which multiple indicators of aberrant plastid function in Arabidopsis are integrated upstream of GUN1 within plastids, which leads to ABI4-mediated repression of nuclear-encoded genes.
Plastid-to-nucleus retrograde signaling.
This review summarizes the current understanding of plastid-to-nucleus retrograde signaling, which involves multiple, partially redundant signaling pathways that are dependent on the redox state of photosynthetic electron transport components.
Intracellular Signaling from Plastids to the Nucleus
Several signaling pathways are connected to a communication network in which light signals are also involved, and leads to up- and down-regulation in the expression of certain nuclear genes.
Intracellular Signaling and Chlorophyll Synthesis
Future work in this area should provide detailed molecular information on the influence of chlorophyll synthesis and other plastid-localized metabolism on nuclear gene expression and how plants utilize this form of interorganellar communication during their lifecycles.
The genomes uncoupled-dependent signalling pathway coordinates plastid biogenesis with the synthesis of anthocyanins
It is proposed that regulation of PHANGs and genes contributing to anthocyanin biosynthesis are two, albeit oppositely, co-regulated processes during plastid biogenesis.
GUN control in retrograde signaling: How GENOMES UNCOUPLED proteins adjust nuclear gene expression to plastid biogenesis.
This review article summarizes the current understanding of GUN-related retrograde signaling and provides a critical appraisal of the various proposed roles for GUNs and their respective pathways.
Influence of plastids on light signalling and development
  • R. Larkin
  • Biology, Environmental Science
    Philosophical Transactions of the Royal Society B: Biological Sciences
  • 2014
GUN-dependent plastid-to-nucleus signalling is reviewed, the flaws in the major criticisms of the gun mutant screen are explained and the influence of plastids on light signalling and development is reviewed.
A number of studies have indicated that proper expression of nuclear genes that encode proteins with functions related to photosynthesis is dependent on normal chloroplast development in diverse monocotyledonous and dicotylingonous genome was lost or transferred to the nucleus of the eukaryotic host.
Plastid-to-nucleus signalling.
  • Å. Strand
  • Biology
    Current opinion in plant biology
  • 2004


Pathways of plastid-to-nucleus signaling.
Chloroplast to nucleus communication triggered by accumulation of Mg-protoporphyrinIX
It is shown that the tetrapyrrole intermediate Mg-protoporphyrin (Mg-ProtoIX) acts as a signalling molecule in one of the signalling pathways between the chloroplast and nucleus.
Arabidopsis genomes uncoupled 5 (GUN5) mutant reveals the involvement of Mg-chelatase H subunit in plastid-to-nucleus signal transduction.
It is suggested that certain perturbations of the tetrapyrrole biosynthetic pathway generate a signal from chloroplasts that causes transcriptional repression of nuclear genes encoding plastid-localized proteins.
Characterization of a Family of Chlorophyll-Deficient Wheat (Triticum) and Barley (Hordeum vulgare) Mutants with Defects in the Magnesium-Insertion Step of Chlorophyll Biosynthesis
It is suggested that a block in Mg-chelatase activity in these mutants could account for the other traits of their pleiotropic phenotype previously described in the literature.
Measurement of heme efflux and heme content in isolated developing chloroplasts.
Picomole quantities of heme were measured by reconstitution of the heme with apo-peroxidase and subsequent determination of peroxid enzyme activity and may be indicative of a ;free heme pool' which exists in the chloroplast.
Mechanism and regulation of Mg-chelatase.
The recent design of an in vitro assay combined with the identification of Bchl-biosynthetic enzyme genes has now made it possible to address the question of regulation of Mg-chelatase.
Signal Transduction between the Chloroplast and the Nucleus Article, publication date, and citation information can be found at
This work has shown that chloroplasts are essential for the unique photoautotrophic and sessile existence of higher plants, and these proteins are encoded by both nuclear and chloroplast genomes.
Magnesium-Chelatase from Developing Pea Leaves: Characterization of a Soluble Extract from Chloroplasts and Resolution into Three Required Protein Fractions
The soluble extract was separated into three fractions by chromatography on blue agarose, followed by size-selective centrifugal ultrafiltration of the column flow-through, demonstrating that the plant Mg-chelatase requires at least three protein components.