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A predicted plastid rhomboid protease affects phosphatidic acid metabolism in Arabidopsis thaliana.

ABSTRACT: The thylakoid membranes of the chloroplast harbor the photosynthetic machinery that converts light into chemical energy. Chloroplast membranes are unique in their lipid makeup, which is dominated by the galactolipids mono- and digalactosyldiacylglycerol (MGDG and DGDG). The most abundant galactolipid, MGDG, is assembled through both plastid and endoplasmic reticulum (ER) pathways in Arabidopsis, resulting in distinguishable molecular lipid species. Phosphatidic acid (PA) is the first glycerolipid formed by the plastid galactolipid biosynthetic pathway. It is converted to substrate diacylglycerol (DAG) for MGDG Synthase (MGD1) which adds to it a galactose from UDP-Gal. The enzymatic reactions yielding these galactolipids have been well established. However, auxiliary or regulatory factors are largely unknown. We identified a predicted rhomboid-like protease 10 (RBL10), located in plastids of Arabidopsis thaliana, that affects galactolipid biosynthesis likely through intramembrane proteolysis. Plants with T-DNA disruptions in RBL10 have greatly decreased 16:3 (acyl carbons:double bonds) and increased 18:3 acyl chain abundance in MGDG of leaves. Additionally, rbl10-1 mutants show reduced [14 C]-acetate incorporation into MGDG during pulse-chase labeling, indicating a reduced flux through the plastid galactolipid biosynthesis pathway. While plastid MGDG biosynthesis is blocked in rbl10-1 mutants, they are capable of synthesizing PA, as well as producing normal amounts of MGDG by compensating with ER-derived lipid precursors. These findings link this predicted protease to the utilization of PA for plastid galactolipid biosynthesis potentially revealing a regulatory mechanism in chloroplasts.

SUBMITTER: Lavell A

PROVIDER: S-EPMC6711814 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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A predicted plastid rhomboid protease affects phosphatidic acid metabolism in Arabidopsis thaliana.

Lavell Anastasiya A Froehlich John E JE Baylis Olivia O Rotondo Anthony D AD Benning Christoph C

The Plant journal : for cell and molecular biology 20190607 5

The thylakoid membranes of the chloroplast harbor the photosynthetic machinery that converts light into chemical energy. Chloroplast membranes are unique in their lipid makeup, which is dominated by the galactolipids mono- and digalactosyldiacylglycerol (MGDG and DGDG). The most abundant galactolipid, MGDG, is assembled through both plastid and endoplasmic reticulum (ER) pathways in Arabidopsis, resulting in distinguishable molecular lipid species. Phosphatidic acid (PA) is the first glycerolipi ...[more]

PMID: 31062431

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Project description:BACKGROUND: Plastids arose from a free-living cyanobacterial endosymbiont and multiply by binary division as do cyanobacteria. Plastid division involves nucleus-encoded homologs of cyanobacterial division proteins such as FtsZ, MinD, MinE, and ARC6. However, homologs of many other cyanobacterial division genes are missing in plant genomes and proteins of host eukaryotic origin, such as a dynamin-related protein, PDV1 and PDV2 are involved in the division process. Recent identification of plastid division proteins has started to elucidate the similarities and differences between plastid division and cyanobacterial cell division. To further identify new proteins that are required for plastid division, we characterized previously and newly isolated plastid division mutants of Arabidopsis thaliana. RESULTS: Leaf cells of two mutants, br04 and arc2, contain fewer, larger chloroplasts than those of wild type. We found that ARC2 and BR04 are identical to nuclear genes encoding the plastid chaperonin 60 alpha (ptCpn60alpha) and chaperonin 60 beta (ptCpn60beta) proteins, respectively. In both mutants, plastid division FtsZ ring formation was partially perturbed though the level of FtsZ2-1 protein in plastids of ptcpn60beta mutants was similar to that in wild type. Phylogenetic analyses showed that both ptCpn60 proteins are derived from ancestral cyanobacterial proteins. The A. thaliana genome encodes two members of ptCpn60alpha family and four members of ptCpn60beta family respectively. We found that a null mutation in ptCpn60alpha abolished greening of plastids and resulted in an albino phenotype while a weaker mutation impairs plastid division and reduced chlorophyll levels. The functions of at least two ptCpn60beta proteins are redundant and the appearance of chloroplast division defects is dependent on the number of mutant alleles. CONCLUSION: Our results suggest that both ptCpn60alpha and ptCpn60beta are required for the formation of a normal plastid division apparatus, as the prokaryotic counterparts are required for assembly of the cell division apparatus. Since moderate reduction of ptCpn60 levels impaired normal FtsZ ring formation but not import of FtsZ into plastids, it is suggested that the proper levels of ptCpn60 are required for folding of stromal plastid division proteins and/or regulation of FtsZ polymer dynamics.

Dataset Information

A predicted plastid rhomboid protease affects phosphatidic acid metabolism in Arabidopsis thaliana.

Publications

A predicted plastid rhomboid protease affects phosphatidic acid metabolism in Arabidopsis thaliana.

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