PLANT TELOMERES AND TELOMERASES - A REVIEW

Barbara McClintock began investigating plant telomeres during the 1930 s, but little additional work was done in this area until a telomeric DNA sequence was isolated and characterized from Arabidopsis thaliana in 1988, This sequence, a simple repeat of the heptanucleotide 5'-TTTA GGG-3', has been found in telomeres of almost all plants analyzed, Tel omere length in plants. which can be a long as 75 kb or as short as 2 kb, is controlled bu both genetic and developmental factors. The major mechanism for synthesis of telomeres is telomerase, a ribonucleoprote in sith reverse transcriptase activity. Telomerase expression is highl y regulated in both plants and animals. For example, there is little o r no detectable expression of telomerase in most vegetative tissues of plants nor in mast somatic tissues of animals. In contrast to animals , plants do not specific a germ line until late in development, but te lomerase is reactivated during flowering, possibly to ensure that game tes and embryos arising from them inherit fully functional chromosomes . Telomerase is also highly expressed in plant tissue culture cells, a s might be expected for cells with an unlimited capacity for prolifera tion. Despite recent progress in investigating plant telomeres and tel omerase at the molecular level. there is still much more to learn, esp ecially concerning the developmental control of telomerase activity.