Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Theses & dissertations (Interdisciplinary)



First Advisor

Thomas A. Peterson


The maize P gene encodes a Myb-homologous regulator of red phlobaphene pigment biosynthesis in the pericarp, cob and other floral tissues. The P locus has a unique structure with two 5.2kb direct repeats flanking the P gene coding region. When the transposon (Ac) inserts into one site between the two direct repeats in the P-ovov-1114 allele, homologous recombination between the two 5.2kb repeats can occur and the whole P gene coding sequence is deleted;To further study this transposon-induced homologous recombination. This study examined six alleles that carry Ac insertions at different sites in the P locus, in both orientations. Each allele was tested as a heterozygote with P-wr, in the same hybrid (4Co63/W23) genetic background. After the cross with the r-m3::Ds reporter, the mature ears were examined for the presence of colorless pericarp sectors. We found the alleles with Ac inserted at different sites between the two direct repeats had higher frequency of colorless sector than the alleles with Ac insertions either within or outside the 5' direct repeat. These results suggest that the transposon-induced homologous recombination is enhanced by the insertion of the element between the repeats. Ac orientation might have no effect on homologous recombination at P locus;To test if transposon-induced recombination is a general phenomenon in plants, we transformed Arabidopsis with a construct (GU-Ds-US) containing a stable transposon (Ds) inserted between two deleted GUS parts with homologous direct repeats similar to Ac inserted in maize P locus. Arabidopsis transformants containing GU-Ds-US construct were crossed with Arabidopsis lines containing stable Ac, which provided transposase to activate Ds. The progeny gave >1000 fold higher frequency of the blue spots than the control plants without Ac transposase. Blue spots indicated the homologous recombination and restoration of the GUS gene. Transposon-induced recombination was observed in vegetative and floral organs, and several germinally transmitted events were observed;Therefore, the results demonstrate that transposon-induced homologous recombination can occur at the endogenous maize gene as well as artificial construct in transgenic Arabidopsis. It may be a general effect in plants and could play a role in plant genome evolution.



Digital Repository @ Iowa State University,

Copyright Owner

Yongli Xiao



Proquest ID


File Format


File Size

107 pages