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First published online April 29, 2005; 10.1104/pp.104.058735 Plant Physiology 138:641-653 (2005) © 2005 American Society of Plant Biologists The Arabidopsis IspH Homolog Is Involved in the Plastid Nonmevalonate Pathway of Isoprenoid BiosynthesisDepartment of Genetics, Harvard Medical School, Boston, Massachusetts 02115 (M.H.H., H.M.G.); Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114 (M.H.H., H.M.G.); and Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan (M.H.H.)
Plant isoprenoids are synthesized via two independent pathways, the cytosolic mevalonate (MVA) pathway and the plastid nonmevalonate pathway. The Escherichia coli IspH (LytB) protein is involved in the last step of the nonmevalonate pathway. We have isolated an Arabidopsis (Arabidopsis thaliana) ispH null mutant that has an albino phenotype and have generated Arabidopsis transgenic lines showing various albino patterns caused by IspH transgene-induced gene silencing. The initiation of albino phenotypes rendered by IspH gene silencing can arise independently from multiple sites of the same plant. After a spontaneous initiation, the albino phenotype is systemically spread toward younger tissues along the source-to-sink flow relative to the initiation site. The development of chloroplasts is severely impaired in the IspH-deficient albino tissues. Instead of thylakoids, mutant chloroplasts are filled with vesicles. Immunoblot analysis reveals that Arabidopsis IspH is a chloroplast stromal protein. Expression of Arabidopsis IspH complements the lethal phenotype of an E. coli ispH mutant. In 2-week-old Arabidopsis seedlings, the expression of 1-deoxy-D-xylulose 5-phosphate synthase (DXS), 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR), IspD, IspE, IspF, and IspG genes is induced by light, whereas the expression of the IspH gene is constitutive. The addition of 3% sucrose in the media slightly increased levels of DXS, DXR, IspD, IspE, and IspF mRNA in the dark. In a 16-h-light/8-h-dark photoperiod, the accumulation of the IspH transcript oscillates with the highest levels detected in the early light period (26 h) and the late dark period (46 h). The expression patterns of DXS and IspG are similar to that of IspH, indicating that these genes are coordinately regulated in Arabidopsis when grown in a 16-h-light/8-h-dark photoperiod.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.058735. * Corresponding author; e-mail ming{at}gate.sinica.edu.tw; fax 886227827954. Received December 21, 2004; returned for revision February 26, 2005; accepted February 27, 2005. This article has been cited by other articles:
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