الفهرس 
The tetrapyrrole biosynthesis in photosyntheticOnly 14 pages are availabe for public view
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Abstract
Ferrochelatase ((FC) protoheme ferro-lyase (EC 4.99.1.1))
catalyzes the insertion of ferrous ion into protoporphyrin IX (Proto) to form protoheme. FC is a
single sub unit enzyme encoded by two genes FCI and FCII. The full-length cDNA sequence encoding
tobacco FCII was identified and isolated to produce transgenic plants silencing the FCI gene.
Transgenic tobacco plants were generated to analyze the consequences of inactivation of FCI on the
expression and the activity in the tetrapyrrole biosynthesis pathway. FCI antisense transformants
contained lower FCI transcript levels and a reduced FC activity leading to increased Proto and
decreased heme contents. Interestingly, the ALA synthesizing capacity was altered in transgenic
lines with FCI inactivation, which can be explained by feedback regulation of heme on the initial
step of tetrapyrrole biosynthesis. FCI antisense plants with decreased accumulation of heme, show
increased expression of photosynthesis-associated nuclear genes (PhANGs). These data suggest heme
as a retrograde signal that modulates PhANG expression in the nucleus in response to tetrapyrrole
biosynthesis in chloroplasts.
Another central question regards the unambiguous organellar localization of FCI in higher
plants. Two FCI-fusion gene
constructs with two alternative ATG-initiation codons were
designed to demonstrate subcellular localization of FCI. The in situ expression assays revealed
sole targeting of FCI into chloroplasts, but not into mitochondria.