Date of Award
Master of Science
Genetics, Development and Cell Biology
Philip W. Becraft
The maize Vp1 promoter contains a putative ABA response element (ABRE). The bZIP transcription factor, TRAB1, binds ABREs in seed maturation related gene promoters of other cereals. Database searches, multiple sequence alignment and phylogenetic analysis show that ZmTRAB1 is a putative TRAB1 ortholog in maize. ZmTRAB1 undergoes alternative splicing and two splicing variant cDNAs, designated ZmTRAB1-1, and ZmTRAB1-2 were isolated. As illustrated by gel mobility shift assays, the proteins encoded by each splicing variant could specifically bind to the ABRE in vitro. In spite of a high conserved bZIP domain, the transactivation activity of ZmTRAB1-1 was higher than that of ZmTRAB1-2 in transient assays. The relative GUS activity of a Vp1::GUS reporter cobombarded with ZmTRAB1-2 into maize embryos increased with exogenous ABA, while that of ZmTRAB1-1 showed a statistically insignificant induction by ABA. Taken together, these results suggest that ZmTRAB1 variants are embryo expressed transcription factors that function in ABA signaling.
The maize Vp1 promoter sequence includes a predicted Myb-binding site I (MBSI), TAACTG, to which Myb transcription factors bind in other promoters. A candidate, designated ME97, was isolated in a yeast one-hybrid screen and contained the C-terminal region of a Myb-like protein. As illustrated by gel mobility shift assays, the partial ME97 protein could specifically bind to the MBSI in vitro. The reporter activity of the wild type Vp1 promoter was significantly higher than that of a mutant reporter, changing the MBSI-core sequence AA to CC, both with and without ABA treatment. Taken together, these results suggest that ME97 is embryo expressed transcription factor that may regulate expression of the Vp1 gene through binding to the MBSI.
Seo, Joonbae, "Molecular genetics studies of bZIP transcription factor, TRAB1, and MYB transcription factor, ME97, on the Viviparous 1 promoter in Zea mays" (2008). Graduate Theses and Dissertations. 11151.