UC Riverside

Although every cell contains a full complement of genes, not every gene is expressed equally. It is through different types of regulation that each cell is able to differentiate into various cell types to generate a multi-cellular organism. One such type of regulation is at the transcriptional level. In my thesis work, I have gained a better understanding of how transcriptional regulation occurs in Arabidopsis thaliana through two divergent projects. First, I have characterized the molecular mechanism by which APETALA2 (AP2), a floral homeotic gene, acts in floral development, by identifying its elusive target binding sequence, TTTGTT and/or AACAAA. In addition, I have found that AP2 modulates the expression of AGAMOUS (AG), another floral homeotic gene involved in floral organ specification as well as stem cell maintenance, through this site in vivo. This finding provided a molecular link between AP2 and AG, thereby answering a long-standing question in the field of floral development. Second, using a forward chemical genetics screen for players involved in transcriptional gene silencing, I have identified a chemical, Camptothecin (CPT), which released a transcriptionally silenced luciferase-based reporter. CPT is a well-known anti-cancer compound known to target DNA Topoisomerase Iα. Topoisomerases are used to relieve torsional stress on the DNA double helix during replication. Here in my thesis work, I have found that in Arabidopsis, TOP1α is also involved in transcriptional gene silencing through several different modes: body methylation and RNA-directed DNA methylation. Addition of the chemical resulted in the release of not only DNA methylation at the reporter transgene, but also endogenous loci as well. These findings highlight the diverse functions of TOP1α in development and provide implications in the study of cancer biology.