A drastic reduction in DOF1 transcript levels does not affect C4-specific gene expression in maize

The transcription factor DOF1 has been suggested to regulate photosynthetic gene expression in maize. By screening a RescueMu transposon-tagged mutant library, we identified a maize mutant with a transposon integration in the Dof1 gene 16bp upstream of the transcription initiation site (TIS). Sequencing of the Dof1 promoter region revealed an unusual promoter structure missing any typical elements. Homozygous (ho) mutant tines were generated by selfing and subsequent PCR and DNA get blot analyses. The transposon integration reduced Dof1 transcript levels to less than 20% compared to the wild-type and overlapping RT-PCR systems revealed that these transcripts were not initiated from the native transcription start site. Dof1 transcripts transiently accumulate in wild-type plants after illumination of darkened seedlings, but this accumulation cannot be observed in mutant tines. However, the time-course of transcript accumulation from the C-4-specific phosphoenolpyruvate carboxylase (PEPC) gene, a possible target of DOF1, is not altered. Moreover, no impact on the steady-state levels of five additional transcripts involved in C-4-metabolism can be observed. The contents of amino acids, glucose, and malate as well. as the carbon to nitrogen ratio in the leaves remained unchanged when comparing wild-type and mutant plants. Our data question the importance of DOF1 in the control of photosynthetic gene expression in maize. (C) 2006 Elsevier GmbH. All rights reserved.