Protection of Telomeres 1 Is Required for Telomere Integrity in the Moss Physcomitrella patens  

Abstract

In vertebrates, the single-stranded telomeric DNA binding protein Protection of Telomeres 1 (POT1) shields chromosome ends and prevents them from eliciting a DNA damage response. By contrast, Arabidopsis thaliana encodes two divergent full-length POT1 paralogs that do not exhibit telomeric DNA binding in vitro and have evolved to mediate telomerase regulation instead of chromosome end protection. To further investigate the role of POT1 in plants, we established the moss Physcomitrella patens as a new model for telomere biology and a counterpoint to Arabidopsis. The sequence and architecture of the telomere tract is similar in P. patens and Arabidopsis, but P. patens harbors only a single-copy POT1 gene. Unlike At POT1 proteins, Pp POT1 efficiently bound single-stranded telomeric DNA in vitro. Deletion of the P. patens POT1 gene resulted in the rapid onset of severe developmental defects and sterility. Although telomerase activity levels were unperturbed, telomeres were substantially shortened, harbored extended G-overhangs, and engaged in end-to-end fusions. We conclude that the telomere capping function of POT1 is conserved in early diverging land plants but is subsequently lost in Arabidopsis.

RETRACTED: Two RNA subunits and POT1a are components of Arabidopsis telomerase

“…POT1 from algae, moss, maize, and Asparagales binds telomeric DNA in vitro (10,45). Moreover, moss POT1, like its counterparts in yeast and vertebrates, is required for chromosome end protection (45).…”

Surprises from the Chromosome Front: Lessons from Arabidopsis on Telomeres and Telomerase

“…POT1, on the other hand, is highly conserved in plants, and like its vertebrate counterparts, it is crucial for chromosome end protection in the moss Physcomitrella patens (Shakirov et al 2010). Intriguingly, A. thaliana encodes two full-length POT1 proteins (POT1a and POT1b) as well as a smaller, truncated POT1 (POT1c) (Rossignol et al 2007).…”

“…None of the three AtPOT1 paralogs specifically bind telomeric DNA in vitro (Shakirov et al 2005, 2010). This phenomenon is not a quirk of Arabidopsis , because biochemical analysis of POT1 proteins across the plant kingdom revealed only two examples of DNA binding by one of two POT1 paralogs from Zea mays and the single POT1 protein from green algae (Shakirov et al 2009a,b).…”

Characterization of a PDK1 Homologue from the Moss Physcomitrella patens

“…It should be noted that the reduced colony size of the gene replacement moss lines could be due to improper RNA processing, since the vector used for gene replacement lacks a terminator sequence for the introduced PpPDK1 gene. However, this vector has been used previously for gene replacement without noticeable differences from the wild type (Shakirov et al, 2010;Spinner et al, 2010). Additionally, from the pdk1 knockout line, it appears that the loss of PpPDK1 is not completely lethal but does not produce healthy moss tissue.…”