Chloroplast sensor kinase

Chloroplast Sensor Kinase (CSK) is a protein in chloroplasts of green plants and algae.[1] In the plant Arabidopsis thaliana (thale cress) CSK is the product of the gene At1g67840. CSK is also found in cyanobacteria; prokaryotes from which chloroplasts evolved by endosymbiosis. CSK is an iron-sulfur protein with 3 iron and 4 sulphur atoms in its redox-active site.[2] It has a midpoint redox potential of −15 mV at pH 8, which is consistent with its autophosphorylation communicating the redox state of the plastoquinone pool to regulation of chloroplast DNA transcription[3] – specifically of genes for proteins at the photochemical reaction center of photosystem I. CSK and its redox regulatory function are inherited from the prokaryotic, cyanobacterial ancestor of chloroplasts. CSK is a prediction of the CoRR Hypothesis for genes in organelles.[4][5][6] CSK is intrinsic to chloroplasts, targeted to chloroplast genes, and may have been required for the retention, in evolution, of chloroplast DNA.

Notes
  1. Puthiyaveetil S, Kavanagh TA, Cain P, Sullivan JA, Newell CA, Gray JC, Robinson C, van der Giezen M, Rogers MB, Allen JF (2008) The ancestral symbiont sensor kinase CSK links photosynthesis with gene expression in chloroplasts. Proceedings of the National Academy of Sciences of the United States of America 105: 10061-10066
  2. Ibrahim IM et al. (2020) An evolutionarily conserved iron-sulfur cluster underlies redox sensory function of the Chloroplast Sensor Kinase. Communications Biology 3: 13 https://doi.org/10.1038/s42003-019-0728-4 .
  3. Pfannschmidt T et al. (1999) Photosynthetic control of chloroplast gene expression. Nature 397: 625–628.
  4. Allen JF (1993) Control of gene expression by redox potential and the requirement for chloroplast and mitochondrial genomes. Journal of Theoretical Biology 165: 609–631
  5. Allen JF (2015) Why chloroplasts and mitochondria retain their own genomes and genetic systems: colocation for redox regulation of gene expression. Proceedings of the National Academy of Sciences of the United States of America 112: 10231–10238
  6. Allen JF (2017) The CoRR hypothesis for genes in organelles. Journal of Theoretical Biology, doi:10.1016/j.jtbi.2017.04.008
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