Telomeres and Their Relevance to the Life and Death of Seeds

Abstract

Referee: Professor A. Carl Leopold, Boyce Thompson Institute for Plant Research, Cornell University, Tower Road, Ithaca, NY 14853The highly conserved multiple repeats of short oligonucleotide sequences that cap the ends of eukaryotic chromosomes have become of increasing interest and speculation as their relationship with cell cycling and cell life-spans has been revealed. Most new information has come from the study of animal cells, where the progressive loss of telomeres at each division in somatic cell cultures acts as a “mitotic clock” with cell crisis and death occurring after a prescribed number of cycles. The importance of these closely similar sequences in cell division and cell survival in different parts of plants is much less clear. For seeds and their mature embryos, where no cell division occurs once they are dry, the means for maintaining telomere multiples for viability and successful germination is an intriguing question.This review describes a number of aspects of telomeres in eukaryotes. First, their discovery in seeds of Zea mays, their structure and unusual replication by the enzyme telomerase, which, unlike other polymerases, possesses a reverse transcriptase function from an encoded telomere RNA. Then, evidence that loss of capping telomere multiples could be responsible for cell cycle arrest or programmed cell death. Finally, how restoration of telomere repeats can lead to the immortalization of cell lines in both plants and animals.Although there are differences between plants and animals and seeds seem a special case, a correlation between the maintenance of telomere repeats and the deferral of senescence and cell death appears to exist. It is clear from the remarkable commonality of these telomeric termini that they have an intrinsic part to play in retaining nuclear chromosome stability in growing plant cells, but they may also be markers of the maintenance of genomic integrity in the embryos of dry and germinating seeds.