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A Chloroplastic UDP-Glucose Pyrophosphorylase from Arabidopsis Is the Committed Enzyme for the First Step of Sulfolipid Biosynthesis^[W],[OA]

^a RIKEN Plant Science Center, Tsurumi-ku, Yokohama 230-0045, Japan
^b Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8501, Japan
^c Research Center for the Evolving Earth and Planets, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8501, Japan
^d Japan Science and Technology Agency, Core Research for Evolutional Science and Technology, Kawaguchi, 332-0012, Japan
^e Center for Biological Resources and Informatics, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8501, Japan
^f Graduate School of Pharmaceutical Sciences, Chiba University, Inage-ku, Chiba 263-8522, Japan

¹ Address correspondence to ksaito{at}psc.riken.jp.

Plants synthesize a sulfur-containing lipid, sulfoquinovosyldiacylglycerol, which is one of three nonphosphorus glycerolipids that provide the bulk of the structural lipids in photosynthetic membranes. Here, the identification of a novel gene, UDP-glucose pyrophosphorylase3 (UGP3), required for sulfolipid biosynthesis is described. Transcriptome coexpression analysis demonstrated highly correlated expression of UGP3 with known genes for sulfolipid biosynthesis in Arabidopsis thaliana. Liquid chromatography–mass spectrometry analysis of leaf lipids in two Arabidopsis ugp3 mutants revealed that no sulfolipid was accumulated in these mutants, indicating the participation of UGP3 in sulfolipid biosynthesis. From the deduced amino acid sequence, UGP3 was presumed to be a UDP-glucose pyrophosphorylase (UGPase) involved in the generation of UDP-glucose, serving as the precursor of the polar head of sulfolipid. Recombinant UGP3 was able to catalyze the formation of UDP-glucose from glucose-1-phosphate and UTP. A transient assay using fluorescence fusion proteins and UGPase activity in isolated chloroplasts indicated chloroplastic localization of UGP3. The transcription level of UGP3 was increased by phosphate starvation. A comparative genomics study on UGP3 homologs across different plant species suggested the structural and functional conservation of the proteins and, thus, a committing role for UGP3 in sulfolipid synthesis.

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