Journal Article

Cloning of the Gene Encoding a Protochlorophyllide Reductase: the Physiological Significance of the Co-Existence of Light-Dependent and -Independent Protochlorophyllide Reduction Systems in the Cyanobacterium <i>Plectonema boryanum</i>

Yuichi Fujita, Hidenori Takagi and Toshiharu Hase

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 39, issue 2, pages 177-185
Published in print February 1998 | ISSN: 0032-0781
Published online February 1998 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/oxfordjournals.pcp.a029355
Cloning of the Gene Encoding a Protochlorophyllide Reductase: the Physiological Significance of the Co-Existence of Light-Dependent and -Independent Protochlorophyllide Reduction Systems in the Cyanobacterium Plectonema boryanum

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Cyanobacteria have two protochlorophyllide (Pchlide) reductases catalyzing the conversion of Pchlide to chloro-phyllide, a key step in the biosynthetic pathway of chlorophylls (Chls); a light-dependent (LPOR) and a light-independent (DPOR) reductase. We found an open reading frame (ORF322) in a 2,131-bp EcoRI fragment from the genomic DNA of the cyanobacterium Plectonema boryanum. Because the deduced amino acid sequence showed a high similarity to those of various plant LPORs and the LPOR activity was detected in the soluble fraction of Esche-richia coli cells over-expressing the ORF322 protein, ORF322 was defined as the por gene encoding LPOR in P. boryanum. A por-disrupted mutant, YFP12, was isolated by targeted mutagenesiss to investigate the physiological importance of LPOR. YFP12 grew as well as wild type under low light conditions (10-25 μE m−2 S−1). However, its growth was significantly retarded as a result of a significant decrease in its Chl content under higher light conditions (85-130 μE m−2 s−1). Furthermore, YFP12 stopped growing and suffered from photobleaching under the highest light intensity (170 μE m−2 s−1). In contrast, a chlL-dis-rupted (DPOR-less) mutant YFC2 grew as well as wild type irrespective of light intensity. From these phenotypic characteristics, we concluded that, although both LPOR and DPOR contribute to Chl synthesis in the cells growing in the light, the extent of the contribution by LPOR increases with increasing light intensity; without it, the cells are unable to grow under light intensities of more than 130 μ Em−2s-.

Keywords: Chlorophyll biosynthesis; Cyanobacterium; Plectonema boryanum; por; Protochlorophyllide reductase.

Journal Article.  0 words. 

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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