High‐copy sequences reveal distinct evolution of the rye B chromosome

Abstract

SummaryB chromosomes (Bs) are supernumerary chromosomes that vary in number among individuals of the same species. Because of their dispensable nature, their non-Mendelian inheritance and their origin from A chromosomes (As), one might assume that Bs followed a different evolutionary pathway from As, this being reflected in differences in their high-copy DNA constitution. We provide detailed insight into the composition and distribution of rye (Secale cereale) B-located high-copy sequences.A-and B-specific high-copy sequences were identified in silico. Mobile elements and satellite sequences were verified by fluorescence in situ hybridization (FISH). Replication was analyzed via EdU incorporation.Although most repeats are similarly distributed along As and Bs, several transposons are either amplified or depleted on the B. An accumulation of B-enriched satellites was found mostly in the nondisjunction control region of the B, which is transcriptionally active and latereplicating. All B-enriched sequences are not unique to the B but are also present in other Secale species, suggesting the origin of the B from As of the same genus.Our findings highlight the differences between As and Bs. Although Bs originated from As, they have since taken a separate evolutionary pathway.

Satellite DNA in Plants: More than Just Rubbish

“…The most widely accepted view is that they are derived from the A chromosome complement [Jamilena et al, 1995a;Martis et al, 2012]. In Secale cereale , although the B chromosomes contained a similar proportion of repeats as the A chromosomes, the 2 differed significantly in composition due to an additional massive accumulation of B-specific satellite repeats [Klemme et al, 2013]. Not all B-enriched sequences are unique to the B, suggesting that B originated from A chromosomes.…”

“…Together with the satellite DNAs found in plant sex chromosomes, this is an unusual case of a satellite DNA family exclusive to a single chromosome pair of the karyotype of one species. In addition to these cases of chromosomespecific satellite DNAs, it has been reported that satellite DNAs also accumulate within B chromosomes [Klemme et al, 2013]. Supernumerary chromosomes or B chromosomes are dispensable genetic material found both in plant and animals [Camacho, 2005].…”

“…Not all B-enriched sequences are unique to the B, suggesting that B originated from A chromosomes. However, these 2 sets of chromosomes have taken separate evolutionary pathways [Klemme et al, 2013]. Rye satellite repeat families including those clustered on the B chromosome are transcriptionally active.…”

Chromosomal differentiation of Tribe Cestreae (Solanaceae) by analyses of 18-5.8-26S and 5S rDNA distribution

“…The morphology of Bs in Cestrum is similar, but differences in composition and size of heterochromatin blocks suggest that they have been originated independently from each other (Fregonezi et al 2004). This hypothesis needs to be verified, since the variation in heterochromatin observed in the Bs may be also explained by their rapid evolution (Houben et al 2014), which make them subject of structural changes such as accumulation of repetitive DNAs (Lamb et al 2007;Klemme et al 2013). …”

Structural polymorphisms and distinct genomic composition suggest recurrent origin and ongoing evolution of B chromosomes in the Prospero autumnale complex (Hyacinthaceae)

“…Large insertions of plastid and mitochondrial DNA sequences are sometimes detected in plant Bs (Martis et al ., 2012; Klemme et al ., 2013; Ruban et al ., 2014), although none have been found in P. autumnale Bs. Bs frequently share repeat families with the A complement, but also accumulate B‐specific families (Langdon et al ., 2000; Dhar et al ., 2002; Marques et al ., 2012; Martis et al ., 2012).…”