Date of Award
Doctor of Philosophy
Theses & dissertations (Interdisciplinary)
Thomas A. Peterson
Structural genes encoding enzymes that catalyze each step of flavonoid synthesis are temporally and spatially regulated. It has been shown that specific anthocyanin pigmentation patterns in maize are achieved by the tissue-specific expression of regulatory genes. Moreover, this tissue-specific regulation is a consequence of the generation of different alleles or duplicated copies of regulatory genes during evolution;In contrast, the myb-homologous P1 gene was the only known regulatory gene required for phlobaphene biosynthesis. The isolation and characterization of the P2 gene, reported here, provides direct molecular evidence that the P region contains duplicated genes. Furthermore, the duplicated P1 (herein, P1-rr ) and P2 genes have distinct tissue-specific expression patterns. The diverged 5' regulatory sequences of each gene are proposed to confer their different tissue-specificities. The isolation and characterization of a single copy P-homologous gene (P2-t) from teosinte, and comparison of gene structure and sequences among the P1, P2, and P2-t genes predict a model for generation of the P1/P2 gene complex by gene duplication and subsequent retroelement insertion. The P2 and P1 genes were originally duplicated from an ancestral P gene (closely resembling the teosinte P2-t gene). The duplication generated a tandem repeat of the P gene coding region and 3' flanking region, and thereby placed a P gene coding sequence immediately after a P gene 3 ' flanking sequence in a head-to-tail arrangement. In this unique way, the P1 gene acquired new 5' regulatory sequences. Following the gene duplication, retroelement insertions separated the two genes. The site of retroelement insertions was such as to separate the P2 gene from its 3' flanking region. The displaced 3' flanking region is retained as the 5 ' flanking region of the P1 gene. This additionally explains the origin of the duplicated flanking sequences at the 5' and 3' ends of the P1 gene. The P2 gene function was investigated by screening maize populations for P2 deletion mutants. It was found that complete loss of silk browning is coincident with the deletion of both P1 and P2 genes. These results suggest that the P2 gene is another contributor to maysin synthesis, a flavonoid compound that inhibits corn earworm feeding. The regulatory function of the P2 gene was further characterized by analysis of maize cell cultures which ectopically express the P2 gene. Northern blot analysis indicates that the ectopically expressed P2 gene can activate expression of the target structural genes C2 and A1. The results support a regulatory role for the P2 gene in flavonoid (maysin) biosynthesis. Additionally, cellular distribution of P transcripts and phlobaphene pigments in developing pericarp were investigated in this thesis.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Zhang, Peifen, "Molecular characterization of myb-homologous transcriptional factors of the flavonoid pathway in Zea mays " (1999). Retrospective Theses and Dissertations. 12382.