AUTHOR=Crawford Tim S. , Eaton-Rye Julian J. , Summerfield Tina C. 

TITLE=Mutation of Gly195 of the ChlH Subunit of Mg-chelatase Reduces Chlorophyll and Further Disrupts PS II Assembly in a Ycf48-Deficient Strain of Synechocystis sp. PCC 6803

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.01060

DOI=10.3389/fpls.2016.01060

ISSN=1664-462X

ABSTRACT=<p>Biogenesis of the photosystems in oxygenic phototrophs requires co-translational insertion of chlorophyll <italic>a</italic>. The first committed step of chlorophyll <italic>a</italic> biosynthesis is the insertion of a Mg<sup>2+</sup> ion into the tetrapyrrole intermediate protoporphyrin IX, catalyzed by Mg-chelatase. We have identified a <italic>Synechocystis</italic> sp. PCC 6803 strain with a spontaneous mutation in <italic>chlH</italic> that results in a Gly195 to Glu substitution in a conserved region of the catalytic subunit of Mg-chelatase. Mutant strains containing the ChlH Gly195 to Glu mutation were generated using a two-step protocol that introduced the <italic>chlH</italic> gene into a putative neutral site in the chromosome prior to deletion of the native gene. The Gly195 to Glu mutation resulted in strains with decreased chlorophyll <italic>a</italic>. Deletion of the PS II assembly factor Ycf48 in a strain carrying the ChlH Gly195 to Glu mutation did not grow photoautotrophically. In addition, the ChlH-G195E:ΔYcf48 strain showed impaired PS II activity and decreased assembly of PS II centers in comparison to a ΔYcf48 strain. We suggest decreased chlorophyll in the ChlH-G195E mutant provides a background to screen for the role of assembly factors that are not essential under optimal growth conditions.</p>