Meristem, cell division and S phase-dependent activity of wheat histone H4 promoter in transgenic maize plants

Abstract

We have studied the activity of a wheat histone H4 promoter in transgenic maize plants produced by direct DNA uptake into embryogenic cell suspension protoplasts. Expression patterns revealed by fluorimetric as well as histochemical GUS reporter enzyme assays and Northern hybridisation indicated the cell division-dependent expression of the GUS gene driven by the histone H4 promoter in proliferating cells and meristems. Changes in gene expression associated with the progression through the cell cycle in maize cell-suspension 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 from other S phase-associated genes such as maize histone H4, histone H2B and proliferating cell nuclear antigen ( PCNA) . The reporter gene expression was low during mitosis when accumulation of the transcripts of a B-type mitotic cyclin CycB1;zm;1 could be detected. The presented data indicate that the used 720-bp-long promoter region can provide replication-dependent expression for the GUS reporter gene in transgenic maize. In these maize plants, external hormone stimuli generated by a synthetic auxin 2,4-dichlorophenoxy acetic acid (2,4-D) or abscisic acid (ABA) have modified the histone H4 promoter-driven GUS gene transcription. These findings support the usefulness of the H4::GUS transgenic plants for further studies on cell cycle activation/inactivation by mitogenic or stress related stimuli in maize.