STN7 and GUN1
The thylakoid protein kinase STN7 does not only phosphorylate photosynthetic proteins like light-harvesting complex II but it is also required for the so-called long-term response (LTR), which regulates the acclimation of nuclear and plastid gene expression upon changes in light conditions. Another chloroplast protein, GUN1, was identified in the course of a mutation screen for plants treated with the herbicide norflurazon that can still express the LHCB marker gene. The GUN1 protein integrates three pathways of retrograde signalling (one of them are the OGE-dependent signals, see above) but it does bind proteins rather than nucleic acids although it contains a PPR domain. We are interested in discovering how signals emerge from STN7 and GUN1 and how these signals are transferred to the nucleus for reprogramming gene expression.
Image: Speculative model how signalling by GUN1 (yellow circle) can be triggered by perturbations in plastid gene expression (PGR) or in the tetrapyrrole biosynthesis pathway (TPB)
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