Molecular and physiological characterization of Nicotiana tabacum ferrochelatase I

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.