Analysis of Poly(ADP-Ribose) Polymerases in Arabidopsis Telomere Biology

Kara A. Boltz,Dorothy E. Shippen,Madhu Jasti,Jennifer M. Townley,Arthur J. Lustig

doi:10.1371/journal.pone.0088872

Abstract

Maintaining the length of the telomere tract at chromosome ends is a complex process vital to normal cell division. Telomere length is controlled through the action of telomerase as well as a cadre of telomere-associated proteins that facilitate replication of the chromosome end and protect it from eliciting a DNA damage response. In vertebrates, multiple poly(ADP-ribose) polymerases (PARPs) have been implicated in the regulation of telomere length, telomerase activity and chromosome end protection. Here we investigate the role of PARPs in plant telomere biology. We analyzed Arabidopsis thaliana mutants null for PARP1 and PARP2 as well as plants treated with the PARP competitive inhibitor 3-AB. Plants deficient in PARP were hypersensitive to genotoxic stress, and expression of PARP1 and PARP2 mRNA was elevated in response to MMS or zeocin treatment or by the loss of telomerase. Additionally, PARP1 mRNA was induced in parp2 mutants, and conversely, PARP2 mRNA was induced in parp1 mutants. PARP3 mRNA, by contrast, was elevated in both parp1 and parp2 mutants, but not in seedlings treated with 3-AB or zeocin. PARP mutants and 3-AB treated plants displayed robust telomerase activity, no significant changes in telomere length, and no end-to-end chromosome fusions. Although there remains a possibility that PARPs play a role in Arabidopsis telomere biology, these findings argue that the contribution is a minor one.

Highlights

The essential functions of telomeres are to promote complete replication of the chromosome terminus and to distinguish the natural ends of chromosomes from DNA double-strand breaks (DSBs)
Generation of Plants Null for poly(ADP-ribose) polymerases (PARPs) Activity To examine the role of PARP proteins at Arabidopsis telomeres, we sought to identify mutants lacking PARP1 or PARP2
PARP1 and PARP2 transcription was abolished in single parp1-1 and parp2-1 mutants as indicated by RT-PCR analysis (Figure 1B)

Summary

Introduction

The essential functions of telomeres are to promote complete replication of the chromosome terminus and to distinguish the natural ends of chromosomes from DNA double-strand breaks (DSBs). Telomerase docks on the 39 single-strand (ss) extension on the chromosome end (G-overhang) via contacts with telomere binding proteins. The two main telomere protein complexes are shelterin and CST. Vertebrate shelterin is composed of six core subunits including the double-strand (ds) DNA binding TRF1 and TRF2 (reviewed in [1]). Loss of any of the three CST proteins in plants leads to dramatic telomere shortening, end-to-end chromosome fusions and severe developmental defects that culminate in stem cell failure [3,4,5]. Shelterin plays a more significant role in promoting telomere stability than CST, which acts primarily to facilitate telomeric DNA replication [9,10,11]. While core components of the telomere complex are conserved, their specific contributions to telomere biology are evolving

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Results

Conclusion