Identification and expression analysis of Rehmannia glutinosa mediator complex genes in response to continuous cropping

Abstract

The mediator complex, a conserved assembly of multi-functional proteins, is required for the transcription of almost all protein-encoding genes in eukaryotes. In this report, 36 mediator complex subunit transcripts in Rehmannia glutinosa were identified from a leaf and tuberous root EST database. Nine of these transcripts had integrated open-reading frames (ORFs). A comparison of predicted amino acid sequences with putative mediator complex subunit homologues from another six flowering plants revealed high identities and several conserved domains. Phylogenetic analysis of the nine mediator complex genes in seven flowering plants revealed a closer evolutionary relationship between R. glutinosa and Solanum lycopersicum. The relative abundances of the 36 transcripts were analysed in the leaves and tuberous roots of R. glutinosa. qRT-PCR analysis revealed that the transcripts of approximately one-third of the mediator complex genes investigated in this study were expressed at similar levels. This result suggested that these transcripts might contribute to the formation, maturation or functions of the analysed tissues. The effects of consecutive monoculture on the transcription of R. glutinosa mediator complex genes were also analysed by qRT-PCR. This analysis revealed that one-third of the mediator complex genes presented differential expression patterns in the leaves of second-year plants, whereas over half of the mediator genes were differentially expressed in the tuberous roots of second-year plants. These patterns suggest that one of the subunits of the mediator complex regulates the consecutive monoculture problem in R. glutinosa.