Specialisation of photosynthetic biochemistry in C4 chloroplasts potentiates distinct cell-specific functionality of different chloroplast-to-nucleus retrograde signalling pathways.

In Setaria viridis leaf cell types, chloroplast-to-nucleus retrograde signalling pathways are enriched in a cell-specific manner that tracks C4 photosynthetic biochemistry.

• Why it matters: Chloroplasts sense stress-related ROS to regulate nuclear acclimation, but it is unclear how chloroplast biochemical specialisation aligns with distinct signalling routes in different leaf cells.
• What they did: Using RNA-seq, EPR spectroscopy, and metabolomics on cell type–enriched fractions, plus mutant analyses, the study compared chloroplast-to-nucleus pathway enrichment across mesophyll and bundle sheath cells.
• The result: Singlet oxygen–responsive beta-cyclocitral/dihydroactinidiolide and hydrogen peroxide–responsive PAP pathways were specific to mesophyll cells, while a rapid ROS-independent DHAP-mediated pathway was enriched in bundle sheath cells.

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