Interstitial Telomeric-like Repeats (ITR) in Seed Plants as Assessed by Molecular Cytogenetic Techniques: A Review

Abstract

The discovery of telomeric repeats in interstitial regions of plant chromosomes (ITRs) through molecular cytogenetic techniques was achieved several decades ago. However, the information is scattered and has not been critically evaluated from an evolutionary perspective. Based on the analysis of currently available data, it is shown that ITRs are widespread in major evolutionary lineages sampled. However, their presence has been detected in only 45.6% of the analysed families, 26.7% of the sampled genera, and in 23.8% of the studied species. The number of ITR sites greatly varies among congeneric species and higher taxonomic units, and range from one to 72 signals. ITR signals mostly occurs as homozygous loci in most species, however, odd numbers of ITR sites reflecting a hemizygous state have been reported in both gymnosperm and angiosperm groups. Overall, the presence of ITRs appears to be poor predictors of phylogenetic and taxonomic relatedness at most hierarchical levels. The presence of ITRs and the number of sites are not significantly associated to the number of chromosomes. The longitudinal distribution of ITR sites along the chromosome arms indicates that more than half of the ITR presences are between proximal and terminal locations (49.5%), followed by proximal (29.0%) and centromeric (21.5%) arm regions. Intraspecific variation concerning ITR site number, chromosomal locations, and the differential presence on homologous chromosome pairs has been reported in unrelated groups, even at the population level. This hypervariability and dynamism may have likely been overlooked in many lineages due to the very low sample sizes often used in cytogenetic studies.

Interstitial Arabidopsis-Type Telomeric Repeats in Asteraceae

“…Asteraceae, with nearly 180 analyzed species and subspecies, is the best sampled family of seed plants for the presence of ITR sites in chromosomes [53]. In this paper, we In this case, there was an increase on the frequency of centromeric ITR sites and the concomitant decrease of the interstitial-proximal values.…”

“…Asteraceae, with nearly 180 analyzed species and subspecies, is the best sampled family of seed plants for the presence of ITR sites in chromosomes [53]. In this paper, we have significantly increased the phylogenetic and taxonomic coverage previously known for this family [8,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50].…”

Tracing the Evolution of the Angiosperm Genome from the Cytogenetic Point of View

“…In the wild and non-model genera for which the data on genome sequences are not available, the chromosomal markers (barcodes) such as various repetitive sequences (rDNA, satellite repeats and telomeric repeats) have been used in comparative analyses. There were many studies that have used the repetitive sequences as FISH probes, which enabled the chromosome identification and the comparative analyses of the chromosome structure among related species [ 107 ]. The most often used chromosomal markers are rDNA sequences, which enable the chromosome rearrangements in many groups of closely related species to be hypothesised ( Figure 2 ; [ 89 , 108 , 109 , 110 ]).…”

“…Telomeric sequences are predominantly present in the chromosome termini; however, several species with interstitially located telomeric sequences have been described [ 107 ]. In some species, such a locus could be a trace of the chromosome end to end fusion, translocation or inversion [ 62 , 107 , 113 ].…”

“…Telomeric sequences are predominantly present in the chromosome termini; however, several species with interstitially located telomeric sequences have been described [ 107 ]. In some species, such a locus could be a trace of the chromosome end to end fusion, translocation or inversion [ 62 , 107 , 113 ]. However, in others the interstitial telomeric sequences could be inserted via a translocation with mobile elements or by a mechanism of the rolling-circle replication of extrachromosomal circular DNA [ 62 , 107 , 114 ].…”