Thomas D. McKnight
	Rank	Professor and Associate Head
	Department	Biology
	Phone	(979) 845-3896
	Fax	(979) 845-2891
	Email Address	mcknight@bio.tamu.edu

Regulation of Telomerase in Arabidopsis thaliana
Telomeres are specialized nucleoprotein complexes at the ends of eukaryotic chromosomes that are essential for proper chromosome behavior and stability of the genome. Telomerase, a complex ribonucleoprotein with reverse transcriptase activity, is responsible for synthesizing and maintaining telomeric DNA in most organisms. We are interested in the regulation of telomerase and telomeres in plants because of their central role in maintaining the stability of the genome. Arabidopsis is a genetically-tractable, multicellular organism, and the genetic tools available in this organism make it an ideal system for investigating the regulation of telomerase and telomeres. Although plants and animals became multicellular through independent evolutionary pathways, preliminary work from our lab has shown that the fundamentals of telomere biology are widely conserved. At least some of our results should be applicable to a broad range of eukaryotes, including mammals.

The focus of our current work is to identify genes that regulate telomerase activity by screening activation-tagged lines for mutants that ectopically express telomerase in their leaves. We have already identified and characterized one telomerase regulatory gene. This gene, TELOMERASE ACTIVATOR 1 (TAC1), encodes a previously uncharacterized protein with a single zinc finger that appears to regulate telomerase activity by altering auxin metabolism. We have isolated three other mutants, tac2, tac3, and tac4, that will be characterized to identify their specific telomerase-activating gene. This work should help elucidate fundamental mechanisms for maintaining stability of the plant genome, and at least in part, should be broadly applicable to other eukaryotes. Even the discovery of plant-specific mechanisms will provide illuminating examples for comparative telomere biology.

1. Ren S, Mandadi KK, Boedeker AL, Rathore KS & McKnight TD (2007) Regulation of telomerase in Arabidopsis by BT2, an apparent target of TELOMERASE ACTIVATOR1. Plant Cell 19: 23-31
   
2. Lu H, Gorman E & McKnight TD (2005) Molecular characterization of two anthranilate synthase alpha subunit genes in Camptotheca acuminata. Planta 221: 352-60
   
3. Ren S, Johnston JS, Shippen DE & McKnight TD (2004) TELOMERASE ACTIVATOR1 induces telomerase activity and potentiates responses to auxin in Arabidopsis. Plant Cell 16: 2910-22
   
4. McKnight TD & Shippen DE (2004) Plant telomere biology. Plant Cell 16: 794-803
   
5. McKnight TD, Riha K & Shippen DE (2002) Telomeres, telomerase, and stability of the plant genome. Plant Mol Biol 48: 331-7
   
6. Fitzgerald MS, Shakirov EV, Hood EE, McKnight TD & Shippen DE (2001) Different modes of de novo telomere formation by plant telomerases. Plant J 26: 77-87
   
7. Riha K, McKnight TD, Griffing LR & Shippen DE (2001) Living with genome instability: plant responses to telomere dysfunction. Science 291: 1797-800
   
8. Riha K, McKnight TD, Fajkus J, Vyskot B & Shippen DE (2000) Analysis of the G-overhang structures on plant telomeres: evidence for two distinct telomere architectures. Plant J 23: 633-41
   
9. Hanson RE, Islam-Faridi MN, Crane CF, Zwick MS, Czeschin DG, Wendel JF, McKnight TD, Price HJ & Stelly DM (2000) Ty1-copia-retrotransposon behavior in a polyploid cotton. Chromosome Res 8: 73-6
   
10. Fitzgerald MS, Riha K, Gao F, Ren S, McKnight TD & Shippen DE (1999) Disruption of the telomerase catalytic subunit gene from Arabidopsis inactivates telomerase and leads to a slow loss of telomeric DNA. Proc Natl Acad Sci U S A 96: 14813-8
    
11. Ji Y, De Donato M, Crane CF, Raska WA, Islam-Faridi MN, McKnight TD, Price HJ & Stelly DM (1999) New ribosomal RNA gene locations in Gossypium hirsutum mapped by meiotic FISH. Chromosoma 108: 200-7
    
12. Lu H & McKnight TD (1999) Tissue-specific expression of the beta-subunit of tryptophan synthase in Camptotheca acuminata, an indole alkaloid-producing plant. Plant Physiol 120: 43-52
    
13. McKnight TD, Fitzgerald MS & Shippen DE (1997) Plant telomeres and telomerases. A review. Biochemistry (Mosc) 62: 1224-31
    
14. Vincent RM, LГіpez-Meyer M, McKnight TD & Nessler CL (1997) Sustained harvest of camptothecin from the leaves of Camptotheca acuminata. J Nat Prod 60: 618-9
    
15. Zwick MS, Hanson RE, Islam-Faridi MN, Stelly DM, Wing RA, Price HJ & McKnight TD (1997) A rapid procedure for the isolation of C0t-1 DNA from plants. Genome 40: 138-42
    
16. Ji Y, Raska DA, McKnight TD, Islam-Faridi MN, Crane CF, Zwick MS, Hanson RE, Price HJ & Stelly DM (1997) Use of meiotic FISH for identification of a new monosome in Gossypium hirsutum L. Genome 40: 34-40
    
17. Fitzgerald MS, McKnight TD & Shippen DE (1996) Characterization and developmental patterns of telomerase expression in plants. Proc Natl Acad Sci U S A 93: 14422-7
    
18. Hanson RE, Islam-Faridi MN, Percival EA, Crane CF, Ji Y, McKnight TD, Stelly DM & Price HJ (1996) Distribution of 5S and 18S-28S rDNA loci in a tetraploid cotton (Gossypium hirsutum L.) and its putative diploid ancestors. Chromosoma 105: 55-61
    
19. Hanson RE, Zwick MS, Choi S, Islam-Faridi MN, McKnight TD, Wing RA, Price HJ & Stelly DM (1995) Fluorescent in situ hybridization of a bacterial artificial chromosome. Genome 38: 646-51
    
20. LГіpez-Meyer M, Nessler CL & McKnight TD (1994) Sites of accumulation of the antitumor alkaloid camptothecin in Camptotheca acuminata. Planta Med 60: 558-60
    

Publications list from Pubmed