Hierarchical Patterns of Transgene Expression Indicate Involvement of Developmental Mechanisms in the Regulation of the Maize P1-rr Promoter

Corresponding author: Thomas Peterson, Department of Zoology and Genetics and Department of Agronomy, 2206 Molecular Biology Bldg., Iowa State University, Ames, IA 50011., thomasp{at}iastate.edu (E-mail)

Communicating editor: K. J. NEWTON

The maize P1-rr gene encodes a Myb-homologous transcription factor that regulates the synthesis of red flavonoid pigments. Maize plants transformed with segments of the P1-rr promoter driving a GUS reporter gene exhibit significant variation in transgene expression, both between independent transformation events and among sibling plants derived from a single event. Interestingly, variability in spatial expression is not random; rather, transgene activity occurs predominantly in five patterns that fit a hierarchy: expression is most common in kernel pericarp, with sequential addition of expression in cob glumes, husk, silk, and tassel. The hierarchical expression pattern of P-rr::GUS transgenes suggests a possible model for developmental regulation of the P1-rr gene. Our results demonstrate that variability in transgene expression, a common occurrence in transgenic plant studies, can be informative if adequately analyzed to uncover underlying patterns of gene expression.

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