Reduction of mRNA Levels for the 28.5 kDa Iron-Sulfur Core Protein of Mitochondrial Complex I Inhibits Pollen Maturation in Transgenic Tobacco

Abstract: The multi-subunit enzyme complex I of the mitochondrial respiratory chain is an assembly of nuclear and organ-ellar encoded proteins with distinct roles and functions. The nuclear encoded 28.5 kDa iron-sulfur protein is located at the centre of electron transfer to ubiquinone. Functional importance and regulatory tolerance of this subunit were investigated in transgenic tobacco plants carrying antisense constructs driven by the CaMV 35S promoter. In all of the regenerated transgenics vegetative growth is undisturbed, while in many transformants flower development is abnormal and pollen fertility is reduced. Maximal observed suppression of the steady-state 28.5 kDa mRNA level reaches only about 30%. Apparently, further reduction is lethal to the vegetative tobacco plants, suggesting that the 28.5 kDa subunit is regulated from the steady-state level onwards with little tolerance and no additional possibilities for compensation. This contrasts with the higher flexibility of the NADH-binding subunit of complex I, which vegetatively survives a 70% reduction of its mRNA level.