Date of Award

2016

Document Type

Open Access Dissertation

Department

Biological Sciences

Sub-Department

College of Arts and Sciences

First Advisor

Beth A. Krizek

Abstract

AINTEGUMENTA (ANT) and AINTEGUMENTA-LIKE6 (AIL6) encode related transcription factors with partially overlapping roles in floral organ development in the model plant Arabidopsis thaliana. ANT and AIL6 do not make equivalent contributions to these processes. Loss of ANT function by itself results in smaller flowers, demonstrating that the role of ANT in organ size control cannot be provided by AIL6. Loss of AIL6 function on its own has no phenotypic consequences indicating that all of its roles in flower development can be provided by ANT or some other genes. To further probe the function of AIL6 in flower development, we investigated the molecular basis for the distinct functions of ANT and AIL6 and began to characterize the AIL6 protein. To determine whether the functional differences between ANT and AIL6 are a consequence of differences in gene expression and/or protein activity, we made transgenic plants in which a genomic copy of AIL6 was expressed under the control of the ANT promoter (i.e. ANT:gAIL6). ANT:gAIL6 can rescue the floral organ size defects of ant mutants when AIL6 is expressed at similar levels as ANT in wild type. Thus, the functional differences between ANT and AIL6 result primarily from gene expression differences. However, ANT:gAIL6 ant lines that express AIL6 at higher levels display additional phenotypes including reduced numbers of floral organs, mosaic floral organs, subtending filaments or bracts, and bigger petals. The severity of these phenotypes correlates with overall AIL6 mRNA levels. Such phenotypes were not observed in previously characterized transgenic lines in which the coding region of AIL6 (cAIL6) was expressed under the constitutive 35S promoter. In some 35S:cAIL6 lines, larger flowers are produced, similar to transgenic plants that overexpress ANT. To further investigate the basis for these phenotypic differences in AIL6 overexpression lines, we made two different inducible AIL6 transgenic lines. Induction of AIL6 activity in both of these lines resulted in distinct floral phenotypes depending on the developmental stage of the flower at the time of treatment. Induction of high AIL6 activity in older flowers resulted in larger floral organs while induction of high AIL6 activity in younger flowers resulted in the production of petaloid sepals and in some cases other mosaic floral organs. Furthermore, we show that the distinct phenotypes observed in different AIL6 overexpression lines are likely explained by differences in both the levels and spatial/temporal accumulation of AIL6 mRNA. Initial investigations into AIL6 protein activity show that AIL6 can activate transcription in yeast through a promoter containing ANT consensus binding sites, suggesting that AIL6 has similar DNA binding specificities as ANT. Using chromatin immunoprecipitation assays, we identified floral organ identity genes as potential targets of AIL6 regulation. Our results contribute to our understanding of flower development and identify potential genetic tools to engineer flowers with altered floral organ identity and size.

Rights

© 2016, Han Han

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