Honors Theses

Date of Award


Document Type

Undergraduate Thesis



First Advisor

Sarah Liljegren

Relational Format



Abscission, the shedding of plant organs, is a key process in plant development. Abscission takes place in highly regulated regions called abscission zones (AZ). ARABIDOPSIS THALIANA HOMEOBOX GENE1 (ATH1) and SHOOT MERISTEMLESS (STM) are organ boundary transcription factors that have previously been observed to play a role in sepal-stem boundary formation. Plants carrying mutations in both genes have flowers in which the sepal-stem boundary is abolished. The double mutant flowers are also observed to retain all floral organs. Because abscission zones in Arabidopsis form at organ boundary regions, we hypothesized that the STM and ATH1 transcription factors play a role in abscission zone differentiation. An important gene known to be expressed in floral organ AZs is HAESA (HAE). HAE is a transmembrane receptor kinase that activates the MAP kinase signaling cascade required for cell separation. As a first test of our hypothesis that the STM and ATH1 transcription factors are involved in organ abscission, I analyzed the expression of HAE in wild-type and in stm ath1 double mutant plants. This experiment was conducted using a HAE:GUS transgene. In my results I found that in stm ath1 double mutant plants expression of HAE was substantially reduced in the regions where the floral organ abscission zones would normally form. My results provide the first molecular evidence that the ATH1 and STM transcription factors are critical for the regulation of HAESA expression and the process of abscission zone signaling.

Included in

Biology Commons



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