Description
B chromosomes (Bs) are dispensable components of the genomes of numerous species. Thus far, there is a lack of evidence
for any transcripts of Bs in plants, with the exception of some rDNA sequences. Here, we show that the Giemsa bandingpositive
heterochromatic subterminal domain of rye (Secale cereale) Bs undergoes decondensation during interphase.
Contrary to the heterochromatic regions of A chromosomes, this domain is simultaneously marked by trimethylated H3K4
and by trimethylated H3K27, an unusual combination of apparently conflicting histone modifications. Notably, both types of
B-specific high copy repeat families (E3900 and D1100) of the subterminal domain are transcriptionally active, although with
different tissue type–dependent activity. No small RNAs were detected specifically for the presence of Bs. The lack of any
significant open reading frame and the highly heterogeneous size of mainly polyadenylated transcripts indicate that the
noncoding RNA may function as structural or catalytic RNA.
; Delgado, Margarida 
