Control of retrograde signaling by rapid turnover of GENOMES UNCOUPLED 1 (Plant Physiol.)

Communication between chloroplast and the nucleus is crucial to accomodate changes in the environment as well as regulate development of the chloroplast itself. Five GENOMES UNCOUPLED (GUN2 to -6) genes were previously described to regulate plastid-to-nucleus communication by affecting the synthesis of tetrapyrrole, constituting the active core of chlorophyll. GUN1 does not affect tetrapyrrole biosynthesis. The locus encodes a petatricopeptide repeat protein (PPR) that is involved in protein-to-protein interactions and chloroplast differentiation. GUN1 has a very short lifespan, as is it constantly degraded by Clp protease, with PPR motifs playing a key role in GUN1 protein stability. Although lines overexpressing GUN1 exhibited early flowering phenotypes, the involvement of retrograde signaling in transition from vegetative to reproductive stage requires further examination. (Summary by Magdalena Julkowska) Plant Physiol. 10.1104/pp.18.00009