Serena Fan (Biochemistry Program, Department of Biology, St. Bonaventure University), Anna Hu (Biochemistry Program, Department of Biology, St. Bonaventure University), Xiao-Ning Zhang (Biochemistry Program, Department of Biology, St. Bonaventure University)

Abstract:
The evolutionary conserved apoptosis-and splicing associated protein (ASAP) complex is involved in the regulation of different aspects of RNA metabolism. In Arabidopsis thaliana, the ASAP complex is comprised of Serine/Arginine-rich45 (SR45), Acinus, and Sin3-associated protein 18 (SAP18). Previous studies suggest that the ASAP complex binds to the flowering suppressor FLC gene to reduce its expression and allow normal flowering. In the sr45-1 null mutant, there is a higher FLC expression and a delayed flowering. In addition, SAP18 protein abundance is lower in sr45-1, particularly in the nucleus, suggesting that SR45 is required for a normal level of SAP18 protein. Taken together, we hypothesize that SR45 regulates SAP18 at the protein level to keep a low FLC expression and normal flowering. To test this hypothesis, we first examined the rate of translation and degradation of SAP18 protein in both wildtype (Col-0) and sr45-1 mutant. The results showed a greater rate of degradation of SAP18 protein in sr45-1 . To see if restoring nuclear SAP18 in sr45-1 would lead to a decrease in FLC expression and the normal flowering, transgenic plants were created by overexpressing a DEX-inducible gSAP18-GFP. The T2 generation was screened to confirm the expression of the transgene in the wildtype and the sr45-1 mutant. Under the confocal microscope, the Col-0 transgenics displayed GFP signals in the nucleus after treatment as expected. However, the sr45-1 transgenic had results that did and did not follow the expectations. This may be due to the transgene being inserted to different genome locations that affected its behavior. Next, we are crossing the confirmed Col-0 transgenic lines with sr45-1 to see how the transgene responds to DEX without SR45. Also from confocal microscopy, we observed distinct GFP spots along the edge of the nucleus suggesting that SAP18 may be deposited to condensed chromosomes. Further research is needed to identify the locations of SAP18 on these chromosomal loci.