Molecular and cytogenetic analysis of repetitive DNA in pea (Pisum sativumL.)

A set of pea DNA sequences representing the most abundant genomic repeats w as obtained by combining several approaches. Dispersed repeats were isolate d by screening a short-insert genomic library using genomic DNA as a probe. Thirty-two clones ranging from 149 to 2961 bp in size and from 1000 to 39 000/1C in their copy number were sequenced and further characterized. Fourt een clones were identified as retrotransposon-like sequences, based on thei r homologies to known elements. Fluorescence in situ hybridization using cl ones of reverse transcriptase and integrase coding sequences as probes reve aled that corresponding retroelements were scattered along all pea chromoso mes. Two novel families of tandem repeats, named PisTR-A and PisTR-B, were isolated by screening a genomic DNA library with Cot-1 DNA and by employing genomic self-priming PCR, respectively. PisTR-A repeats are 211-212 bp lon g, their abundance is 2 x 10(4) copies/1C, and they are partially clustered in a secondary constriction of one chromosome pair with the rest of their copies dispersed on all chromosomes. PisTR-B sequences are of similar abund ance (10(4) copies/1C) but differ from the "A" family in their monomer leng th (50 bp), high A/T content, and chromosomal localization in a limited num ber of discrete bands. These bands are located mainly in (sub)telomeric and pericentromeric regions, and their patterns, together with chromosome morp hology, allow discrimination of all chromosome types within the pea karyoty pe. Whereas both tandem repeat families are mostly specific to the genus Pi sum, many of the dispersed repeats were detected in other legume species, m ainly those in the genus Vicia.