Poster: Secondary Metabolism
Abs #
297: Synechocystis PCC6803 gene sll1556, a distant homolog of "Type 2" IPP isomerases, is dispensable under photosynthetic growth conditions.
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Presenter: |
Poliquin, Kelly , poliquin@wam.umd.edu |
Authors | Poliquin, Kelly (A) Ershov, Yuri (B) Cunningham, Jr., Francis X (A) Woreta, Tinsay (A) Gantt, Raymond (A) Gantt, Elisabeth (A) | | Affiliations: |
(A): Department of Cell Biology and Molecular Genetics, University of Maryland
(B): A. N. Bakh Institute, Russian Academy of Sciences
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Isoprenoids in plant chloroplasts, including such essential compounds as chlorophylls, carotenoids, and quinones, are synthesized from isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) produced via the methylerythritol phosphate (MEP) pathway. In contrast to the mevalonate pathway of the plant cytosol compartment, wherein DMAPP is formed from IPP through the action of an IPP isomerase, it is thought IPP and DMAPP are produced separately in the MEP pathway. Why then do plant chloroplasts contain IPP isomerase activity? As a model for plant chloroplasts we have been studying the MEP pathway in the cyanobacterium Synechocystis PCC6803. A homolog of IPP isomerase is not present in the genome of Synechocystis, nor can we detect IPP isomerase activity in cell extracts (Ershov et al., FEBS Lett 473: 337-40). However, the genome of Synechocystis does contain a distant homolog (gene sll1556; ca. 32% AA identity) of a ”Type 2” IPP isomerase recently discovered in Streptomyces (Kaneda et al., PNAS 98: 932-37). The purified recombinant product of sll1556 exhibited no IPP isomerase activity in vitro, whereas substantial activity was displayed by the purified Streptomyces enzyme. To gain insight into the function of sll1556, the gene was disrupted. Compared to the wild type, the sll1556 disruption mutant had smaller cells (15% less in diameter), fewer thylakoids (ca. 40% less than wildtype), a more fibrous outer wall layer, and a slightly reduced growth rate under phototrophic growth conditions. The function of sll1556 remains obscure, but it is clearly not essential for photosynthetic growth. The phenotype suggests a role in membrane synthesis and/or cell wall layer formation.
