The Effects of Mutations in the ATH1 and STM Genes on Sepal, Petal, and Stamen Abscission in Arabidopsis thaliana Plants

Floral organ boundaries are areas that allow distinct organs within a flower to differentiate from each other and the underlying stem. Boundary regions are also where abscission zones (AZs) can form, which allow floral organs to abscise, or detach, from the plant. This study takes a look into a pair of genes, ARABIDOPSIS THALIANA HOMEOBOX GENE1 (ATH1) and SHOOT MERISTEMLESS (STM), which code for transcription factors found in Arabidopsis thaliana that are responsible for proper boundary formation and AZ specification. Mutations in one or both of these genes affect AZ formation of specific floral organs. The ATH1 and STM transcription factors belong to the BELL and KNOX homeodomain families respectively. Heterodimerization of these transcriptions factors is necessary for STM to enter into cell nuclei; therefore mutations in any of the BELL-type partners that STM interacts with will affect its ability to regulate gene expression. I investigated the effect of ath1-3 and stm mutations on stamen, petal, and sepal abscission in Arabidopsis flowers. A device consisting of two soft bristled paintbrushes was used to release floral organs if AZs were present and cell separation had already initiated. Data were collected from WT, ath1-3, and stm flowers and from ath1-3/stm double mutant flowers. While all of the outer floral organs were abscised in wild-type flowers, the ath1-3 and stm single mutants retained many of their stamens. In addition to their stamens, the ath1-3/stm double mutants also retained significantly more sepals and petals than wild-type flowers. These results supported my hypothesis that the ATH1 and STM transcription factors are able to play redundant roles in sepal and petal AZ formation.