Diversity of Telomeric Sequences in True Bugs (Heteroptera): New Data on the Infraorders Pentatomomorpha and Cimicomorpha.

Introduction: Telomeric sequences are stable parts of the genome and are widely conserved among higher level taxa (e.g., TTAGG in insects and other arthropods) although exceptions are known and their numbers are increasing with research. The true bug suborder Heteroptera (Hemiptera) includes more than 40,000 species in about 100 families, classified into seven infraorders. Four different telomeric motifs are currently known in Heteroptera, including (TTAGG)n, (TTAGGGATGG)n, (TTAGGGGTGG)n, and (TTAGGGTGGT)n. The canonical "insect" motif (TTAGG)n was found in representatives of two infraorders, Nepomorpha and Cimicomorpha. Derived motifs were found in a few species previously known as TTAGG-negative in the evolutionarily advanced sister infraorders Cimicomorpha and Pentatomomorpha (= Terheteroptera). Here, we studied telomeric motifs in 20 species of true bugs belonging to 10 families of Terheteroptera.

Methods: We used fluorescence in situ hybridization with the "insect" telomeric probe (TTAGG)n and an alternative probe (TTAGGGATGG)n to map the distribution of telomeric sequences in the chromosomes of 8 species of Pentatomomorpha (from the families Pentatomidae, Rhopalidae, Lygaeidae, Geocoridae, and Blissidae). We also analyzed chromosome-level genome assemblies available in the NCBI database for another 4 species of Pentatomomorpha (from Alydidae, Coreidae, and Pentatomidae) and 8 species of Cimicomorpha (from Reduviidae, Miridae, and Anthocoridae).

Results: Overall, we identified telomeric sequences in all but one (Geocoris dispar; Geocoridae) species. The telomeric motif (TTAGGGATGG)n was detected in both Cimicomorpha (in the families Anthocoridae and Miridae) and Pentatomomorpha (in Blissidae, Lygaeidae, Pentatomidae, and Rhopalidae); the motif (TTAGGGGTGG)n was found only in Pentatomomorpha (in Alydidae, Coreidae, and Pentatomidae); and the canonical "insect" motif (TTAGG)n was found in the family Reduviidae (Cimicomorpha). With our new data, telomeric motifs are now known for 40 species of true bugs from 30 genera, 13 families and 3 infraorders, including Nepomorpha, Cimicomorpha, and Pentatomomorpha. Noncanonical motifs are found so far only in the Terheteroptera clade and are dominant in this group, with (TTAGGGATGG)n leading.

Conclusion: Our new data have expanded the understanding of telomere composition and evolution in Cimicomorpha and Pentatomomorpha and suggested that (TTAGGGATGG)n telomeric sequences can be considered ancestral for the entire clade Terheteroptera.