Boom-Bust Turnovers of Megabase-Sized Centromeric DNA in Solanum Species: Rapid Evolution of DNA Sequences Associated with Centromeres.

Centromeres are composed of long arrays of satellite repeats in most multicellular eukaryotes investigated to date. The satellite repeat-based centromeres are believed to have evolved from "neocentromeres" that originally contained only single- or low-copy sequences. However, the emergence and evolution of the satellite repeats in centromeres has been elusive. Potato (Solanum tuberosum) provides a model system for studying centromere evolution because each of its 12 centromeres contains distinct DNA sequences, allowing comparative analysis of homoeologous centromeres from related species. We conducted genome-wide analysis of the centromeric sequences in Solanum verrucosum, a wild species closely related to potato. Unambiguous homoeologous centromeric sequences were detected in only a single centromere (Cen9) between the two species. Four centromeres (Cen2, Cen4, Cen7, and Cen10) in S. verrucosum contained distinct satellite repeats that were amplified from retrotransposon-related sequences. Strikingly, the same four centromeres in potato contain either different satellite repeats (Cen2 and Cen7) or exclusively single- and low-copy sequences (Cen4 and Cen10). Our sequence comparison of five homoeologous centromeres in two Solanum species reveals rapid divergence of centromeric sequences among closely related species. We propose that centromeric satellite repeats undergo boom-bust cycles before a favorable repeat is fixed in the population.

Zhang H ，Koblížková A ，Wang K ，Gong Z ，Oliveira L ，Torres GA ，Wu Y ，Zhang W ，Novák P ，Buell CR ，Macas J ，Jiang J ... -  《-》

Repeatless and repeat-based centromeres in potato: implications for centromere evolution.

Gong Z ，Wu Y ，Koblízková A ，Torres GA ，Wang K ，Iovene M ，Neumann P ，Zhang W ，Novák P ，Buell CR ，Macas J ，Jiang J ... -  《-》

Three potato centromeres are associated with distinct haplotypes with or without megabase-sized satellite repeat arrays.

Wang L ，Zeng Z ，Zhang W ，Jiang J ... -  《-》

Amplification and adaptation of centromeric repeats in polyploid switchgrass species.

Centromeres in most higher eukaryotes are composed of long arrays of satellite repeats from a single satellite repeat family. Why centromeres are dominated by a single satellite repeat and how the satellite repeats originate and evolve are among the most intriguing and long-standing questions in centromere biology. We identified eight satellite repeats in the centromeres of tetraploid switchgrass (Panicum virgatum). Seven repeats showed characteristics associated with classical centromeric repeats with monomeric lengths ranging from 166 to 187 bp. Interestingly, these repeats share an 80-bp DNA motif. We demonstrate that this 80-bp motif may dictate translational and rotational phasing of the centromeric repeats with the cenH3 nucleosomes. The sequence of the last centromeric repeat, Pv156, is identical to the 5S ribosomal RNA genes. We demonstrate that a 5S ribosomal RNA gene array was recruited to be the functional centromere for one of the switchgrass chromosomes. Our findings reveal that certain types of satellite repeats, which are associated with unique sequence features and are composed of monomers in mono-nucleosomal length, are favorable for centromeres. Centromeric repeats may undergo dynamic amplification and adaptation before the centromeres in the same species become dominated by the best adapted satellite repeat.

Yang X ，Zhao H ，Zhang T ，Zeng Z ，Zhang P ，Zhu B ，Han Y ，Braz GT ，Casler MD ，Schmutz J ，Jiang J ... -  《-》

Rapid proliferation and nucleolar organizer targeting centromeric retrotransposons in cotton.

Centromeric chromatin in most eukaryotes is composed of highly repetitive centromeric retrotransposons and satellite repeats that are highly variable even among closely related species. The evolutionary mechanisms that underlie the rapid evolution of centromeric repeats remain unknown. To obtain insight into the evolution of centromeric repeats following polyploidy, we studied a model diploid progenitor (Gossypium raimondii, D-genome) of the allopolyploid (AD-genome) cottons, G. hirsutum and G. barbadense. Sequence analysis of chromatin-immunoprecipitated DNA showed that the G. raimondii centromeric repeats originated from retrotransposon-related sequences. Comparative analysis showed that nine of the 10 analyzed centromeric repeats were absent from the centromeres in the A-genome and related diploid species (B-, F- and G-genomes), indicating that they colonized the centromeres of D-genome lineage after the divergence of the A- and D- ancestral species or that they were ancestrally retained prior to the origin of Gossypium. Notably, six of the nine repeats were present in both the A- and D-subgenomes in tetraploid G. hirsutum, and increased in abundance in both subgenomes. This finding suggests that centromeric repeats may spread and proliferate between genomes subsequent to polyploidization. Two repeats, Gr334 and Gr359 occurred in both the centromeres and nucleolar organizer regions (NORs) in D- and AD-genome species, yet localized to just the NORs in A-, B-, F-, and G-genome species. Contained within is a story of an established centromeric repeat that is eliminated and allopolyploidization provides an opportunity for reinvasion and reestablishment, which broadens our evolutionary understanding behind the cycles of centromeric repeat establishment and targeting.

Han J ，Masonbrink RE ，Shan W ，Song F ，Zhang J ，Yu W ，Wang K ，Wu Y ，Tang H ，Wendel JF ，Wang K ... -  《-》