B chromosomes and their repetitive dna composition in cestrum nocturnum (solanaceae)

Abstract

B chromosomes (Bs) are additional components of thegenome found in more than 15% of plant species. Theyare made up mostly of non-coding repetitive DNA,and their presence can affect the phenotype, beingunfavorable in high number. In Cestrum nocturnumL., the number of Bs varies from 0 to 13, betweenand within individuals, possibly due to meiotic and/or mitotic instability. To understand the repetitivecomposition of Bs, the genome of two individuals of C.nocturnum were sequenced, one with Bs and other onewithout Bs. The results of the analysis showed thatalmost 60% of the genome is made up of repetitive DNAand those families of repetitive DNA with a proportiongreater than 0,540% were considered enriched inthe sample with Bs. The results of a comparativeanalysis between the two genomes showed that Bs ofC. nocturnum are mostly enriched in satellite repeats,rDNA and Ty3-gypsy transposable elements, whichare probably derived from A complement repeatsequences. Within the repetitive DNA enriched inthe sample with Bs, we found transposable elementsTy3-gypsy/Tekay (CL283-0,558%) and Ty3-gypsy/Retand (CL251-0,541%), satellite DNA (Cnoc_sat01_32-0,550%, Cnoc_sat03_78-0,549%, Cnoc_sat04_180-0,546%, Cnoc_sat07_51-0,547% andCnoc_sat10_48-0,557%) and ribosomal DNA 35S(CL117-0.548% and CL216-0.544%) and 5S (CL2180.571%). The distribution of the Bs-enriched repeatswere compared in A and B chromosomes by FISHmapping, with probes labeled directly (FITC andTRICT). The neutral nature of Bs could be one of thebasic principles of the accumulation of repetitivesequences in the genome.