Evolution, Composition and Interrelated Functions of Telomeres and Subtelomeres: Lessons from Plants
Jiří Fajkus, Andrew R. Leitch, Michael Chester and Eva Sýkorová
The terminal parts of chromosomes, telomeres and their subtelomeric neighbors are reviewed. Both have common and specific features that interact to generate the unique and essential biology that characterizes telomeres. The chromatin of both chromosome domains has a nucleosomal structure and their DNA component is often, but not always formed by tandem repeats. The relationships between telomere and subtelomere domains are complex and are discussed at sequence and folding levels. The complexity of the interaction arises from, and enables, the multiple functions of the telomere domain. For example, telomere length influences the expression of genes adjacent to the telomere via controlled heterochromatinization, while at the same time the conformation changes in the heterochromatin influences telomere length regulation. Here we discuss the process of heterochromatinization of terminal chromosome domains, including the role of RNA interference, telomere and subtelomere boundary domains and the evolution of telomere minisatellite and satellite repeats. Variability in telomere sequences and telomere‑maintenance strategies is exemplified by telomere evolution in the plant order Asparagales, which is reviewed together with the latest molecular data on the telomerases that synthesize these variant repeats. We also highlight a surprising interconnectivity between telomere and nucleolar function.