Iowa State University
Pioneer Hi-Bred International, Inc.

Analysis of the 5' region of the P gene as a potential floral-specific promoter
--Xianggam Li, Laura Tagliani, Bruce Drummond, Ben Bowen and Thomas Peterson

The p locus is involved in the synthesis of a phlobaphene-like red pigment found in mature cob glumes and pericarps. The P gene encodes a Myb-like transcription factor (Grotewold, Athma and Peterson, PNAS 88:4587) that binds the sequence CCT/AACC and activates transcription of the A1 gene, but not the Bz1 gene (Grotewold et al., Cell, in press). The 1.2 kb region 5' of the P transcription start site has partial homology to a Trypanosoma brucei tRNA gene, the maize B-I promoter, and maize pollen-specific pectate lyase gene 3' region. The P promoter region was fused to various reporter genes (Gus, luciferase, and anthocyanin markers) for transient assay experiments via particle gun bombardment. The following preliminary results were obtained: (1) the P::GUS reporter fusion was much less active in endosperm suspension culture than either embryogenic cells or BMS non-embryogenic suspension cells; (2) qualitative GUS assays indicated more blue spots in pericarp and cob glumes than aleurone or young shoots; (3) the 5' region of the P gene contains a relatively weak promoter since only P::GUS or P::Luciferase plasmids containing Adh1 intron 1 gave a detectable signal in transient assays, whereas no signal was obtained using similar constructs lacking the Adh1 intron 1. Further subcloning and quantitative assays will be used to understand how the P gene is expressed specifically in floral tissues, and to determine whether the P promoter could be used to direct foreign gene expression in pericarps, glumes, silks and husks. 

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