Abstract
Canonical retrograde signalling comprises information transmission from organelles to the nucleus and in particular controls gene expression for organellar proteins. The need to re-assess this paradigm was suggested by discrepancies between de novo protein synthesis and transcript abundance in response to excess light. Here we uncover major components of a translation-dependent retrograde signalling pathway that first impacts translation and then transcription. The response realization depends on the kinases Mitogen-activated protein kinase 6 (MPK6) and Sucrose non-fermenting 1-related kinase (SnRK1) subunit, AKIN10. Global ribosome foot-printing revealed differential ribosome association of 951 transcripts within 10 min after transfer from low to high light. Despite predominant translational repression, 15 % of transcripts were increased in translation and enriched for chloroplast-localized photosynthetic proteins. About one third of these transcripts, including Stress associated proteins (SAP) 2 and 3, share regulatory motifs in their 5′-UTR that act as binding sites for glyceraldehyde-3-phosphate dehydrogenase (GAPC) and light responsive RNA binding proteins (RBPs). SAP2 and 3 are both translationally regulated and interact with the calcium sensor Calmodulin-like 49 (CML49), which promotes relocation to the nucleus inducing a translation-dependent nuclear stress response. Thus, translation-dependent retrograde signalling bifurcates to directly regulate a translational circuit of chloroplast proteins and simultaneously initiate a nuclear circuit synchronizing retrograde and anterograde response pathways, serving as a rapid mechanism for functional acclimation of the chloroplast.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
↵§ Joint Senior Authorship
Re-submission incorporating revisions from one round of Nature Plants peer-review.
List of Abbreviation
- ABA
- abscisic acid
- A. thaliana
- Arabidopsis thaliana
- AKIN10
- protein kinase being part of the sucrose non-fermenting kinase complex
- Asc
- ascorbate
- CaM
- calmodulin
- CML
- calmodulin-like
- DEG
- differentially expressed gene
- DHA
- dehydroascorbate
- DREB2A
- Dehydration-responsive element binding protein 2
- FC
- fold change
- GAPC
- glyceraldehyde-3-phosphate dehydrogenase 2
- GCN2
- general control non-repressible 2
- GO
- gene ontology
- GSH
- glutathione
- GSSG
- diglutathione disulfide
- HL
- high-light (800 µmol photons m−2 s−1)
- H2O2
- hydrogen peroxide
- HSE
- heat shock element
- HSF
- heat shock factor
- HSP
- heat shock protein
- IRES
- independent ribosomal entry sites
- JA
- jasmonic acid
- LL
- low light (8 µmol photons m−2 s−1)
- log2 FC
- logarithmic fold change to base 2
- MAPK
- mitogen-activated protein kinase
- mbSUS
- mating-based Split-ubiquitin-System
- MBF1c
- Multiprotein Bridging Factor 1C
- OPDA
- 12-oxo-phytodienoic acid
- ORF
- open reading frame
- PEG
- polyethylene glycol
- PET
- photosynthetic electron transport
- PTM
- post-translational modification
- RBP
- RNA binding protein
- ROS
- reactive oxygen species
- RuBisCO
- ribulose bisphosphate carboxylase oxygenase
- SAP
- stress associated protein
- SnRK1
- SNF1Lrelated kinase 1
- TE
- translation efficiency
- TF
- transcription factor
- TOR
- target of rapamycin
- TPT2
- triose phosphate/phosphate translocator 2
- uORF
- upstream open reading frame
- UTR
- untranslated region
- VTC2
- GDP-L-galactose phosphorylase