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Evolutionary rewiring: a modified prokaryotic gene-regulatory pathway in chloroplasts
Sujith Puthiyaveetil1, Iskander M Ibrahim, John F Allen
1School of Biological and Chemical Sciences, Queen Mary University of London, , Mile End Road, London E1 4NS, UK. s.puthiyaveetil@wsu.edu
Summary
Chloroplast sensor kinase (CSK) acts as a SIG1 kinase, regulating chloroplast gene transcription. This novel CSK-SIG1 pathway in plants represses photosystem I gene expression via a phosphoswitch mechanism.
Area of Science:
- Plant molecular biology
- Chloroplast gene regulation
- Photosynthesis research
Background:
- Photosynthetic electron transport influences chloroplast gene transcription via chloroplast sensor kinase (CSK).
- CSK typically functions in bacterial two-component systems but lacks a partner in plants.
- CSK's role in repressing photosystem I (PS I) gene transcription under specific light conditions is known.
Purpose of the Study:
- To investigate the interaction between CSK and SIG1 (sigma factor 1) in chloroplasts.
- To elucidate the mechanism by which CSK regulates PS I gene transcription in plants.
- To characterize the CSK-SIG1 signaling pathway in chloroplasts.
Main Methods:
- Yeast two-hybrid analysis to confirm CSK and SIG1 interaction.
- Biochemical assays to study CSK interaction with quinone.
- Phosphorylation analysis of SIG1 under specific light conditions.
Main Results:
- CSK interacts with SIG1, a component of chloroplast RNA polymerase.
- Arabidopsis SIG1 is phosphorylated in PS I light, leading to repression of PS I genes.
- CSK and SIG1 exhibit similar signaling properties, suggesting CSK is a SIG1 kinase.
Conclusions:
- The CSK-SIG1 system represents a rewired chloroplast signaling pathway.
- A gene-regulatory phosphoswitch in SIG1 mediates selective repression of PS I genes.
- This regulatory mechanism may explain the evolutionary stasis of chloroplast genes.
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