Meristem, cell division and S phase-dependent activity of wheat histone H4promoter in transgenic maize plants

We have studied the activity of a wheat histone H4 promoter in transgenic m aize plants produced by direct DNA uptake into embryogenic cell suspension protoplasts. Expression patterns revealed by fluorimetric as well as histoc hemical GUS reporter enzyme assays and Northern hybridisation indicated the cell division-dependent expression of the GUS gene driven by the histone H 4 promoter in proliferating cells and meristems. Changes in gene expression associated with the progression through the cell cycle in maize cell-suspe nsion cultures were also investigated after partial synchronisation of cell division by aphidicolin or hydroxyurea. The transgene expression regulated by the wheat histone H4 promoter coincided with elevated levels of mRNAs f rom other S phase-associated genes such as maize histone H4, histone H2B an d proliferating cell nuclear antigen (PCNA). The reporter gene expression w as low during mitosis when accumulation of the transcripts of a B-type mito tic cyclin CycB1;zm;1 could be detected. The presented data indicate that t he used 720-bp-long promoter region can provide replication-dependent expre ssion for the GL:S reporter gene in transgenic maize. In these maize plants , external hormone stimuli generated by a synthetic auxin 2,4-dichloropheno xy acetic acid (2,4-D) Or abscisic acid (ABA) have modified the histone H4 promoter-driven GuS gene transcription. These findings support the usefulne ss of the H4::GUS transgenic plants for further studies on cell cycle activ ation/inactivation by mitogenic or stress related stimuli in maize. (C) 199 9 Published by Elsevier Science Ireland Ltd. All rights reserved.