1. Colin Tominey Dr. John Hays Oregon State University 25 September 2009 The Effect of ATR and ATM on UVB-Induced Stem and Progenitor Cell Death in Arabidopsis Root Tips

2. The DNA Damage Response (DDR) DDR is an important signal transduction pathway: –Coordinates cell cycle transitions –Identifies and repairs DNA damage –Can ultimately trigger apoptosis/programmed cell death (PCD) ATR and ATM are major regulators of the DDR pathway

3. ATR and ATM ATR and ATM are kinases Each is activated by a particular type of aberrant DNA structure: –ATR responds to single-stranded DNA –ATM responds to double-strand breaks

4. Apoptosis K.A. Cimprich and D. Cortez. ATR: An Essential Regulator of Genome Integrity. Nat Rev Mol Cell Biol 9 (2008) 616-627.

5. DDR at Blocked Replication Forks Blocked replication forks are an excellent context in which to study DDR Replication complexes are blocked by a number of aberrant DNA structures: –Interstrand crosslinks –Chemically-adducted DNA –Cyclobutane pyrimidine dimers (CPDs) and other UV photoproducts

6. ATR is Not Activated ATR is Activated ATM is Activated Protein Interactions at Blocked Replication Forks R.D. Paulsen and K.A. Cimprich. The ATR pathway: Fine-tuning the fork. DNA Repair 6 (2007) 953-966.

7. TLS- Trans-Lesion Synthesis (Error-Prone Bypass) EFB- Error-Free Bypass Protein Interactions at Blocked Replication Forks

8. Hypotheses ATR is essential in order to utilize Error- Free or Error-Prone Bypass. Both ATR and ATM are independently capable of signaling for programmed cell death (PCD) via SOG1

9. Predictions ATR-deficient Arabidopsis plants will experience an increase in UVB-induced PCD relative to wt plants due to the loss of EFB and EPB options. Arabidopsis plants deficient in both ATR and ATM will experience less UVB- induced PCD relative to wt plants due to the loss of the SOG1-mediated apoptotic pathway.

10. Experimental Design Irradiated 4-day-old Arabidopsis plants (mutants and wt) with UVB and incubated 24h in the dark Stained roots with propidium iodide and counted dead stem and progenitor cells

11. Stem and Progenitor Cells in Arabidopsis Vascular Cortical / Endodermal Columellar / Central Root Cap Epidermal / Lateral Root Cap Stem and Progenitor Cell Types:

12. Results

13. Acknowledgements The Howard Hughes Medical Institute Dr. John Hays Dr. Marc Curtis Buck Wilcox Peter Hoffman Shauna Tominey Dr. Kevin Ahern