Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Theses & dissertations (Interdisciplinary)



First Advisor

Thomas A. Peterson


Myb proteins are defined by a highly conserved DNA-specific binding domain termed Myb, which is composed of approximately 50 amino acids with constantly spaced tryptophan residues. Multiple copies of Myb domains often exist as tandem repeats within a single protein. There are up to four tandem Myb repeats present in Myb proteins identified to date (termed R0R1R2R3 hereafter).;In our study, we collected additional Myb genes, and performed a series of phylogenetic analyses to explore the evolutionary origin of Myb genes. The results suggest that the Myb gene family originated from an ancient one Myb-box gene. One and two intragenic duplications produced R2R3 and R1R2R3 Myb genes, respectively, which then co-existed in the primitive eukaryotes and gave rise to the currently extant Myb genes. Based on our results, we proposed that plant R1R2R3 Myb genes were derived from R2R3 Myb genes by gain of the R1 repeat through an ancient intragenic duplication; this gain model is more parsimonious than the previous proposal that plant R2R3 Myb genes were derived from RlR2R3 Myb genes by loss of the R1 repeat. The phylogenetic analysis of isolated individual Myb repeats indicates that R2 repeat has evolved more slowly than the R1 and R3 repeats. However, it is not clear which repeat is the most ancient one.;Another goal of our project is to classify and predict functions of Myb genes. We clustered the closely-related Myb genes into subgroups from Arabidopsis and rice on a basis of sequence similarity and phylogeny. The gene structure analysis revealed that both the positions and phases of introns are conserved in the same subgroup, although these differ between subgroups. Conserved motifs were detected in C-terminal coding regions within subgroups, and these motifs exist specifically in Myb genes. We also found that Myb genes with similar functions are clustered together. In contrast, no conserved regulatory elements were identified in the divergent non-coding regions. Additionally, the distribution pattern of introns in the phylogenetic tree indicates that Myb domains originally had a compact size without introns. Non-coding sequences were inserted and the splicing sites were conserved during evolution.



Digital Repository @ Iowa State University,

Copyright Owner

Cizhong Jiang



Proquest ID


File Format


File Size

99 pages