A moderately repetitive DNA sequence in alfalfa is transcribed in a floral-specific manner

Based on DNA sequence analysis of 5 clones of repetitive DNA from alfalfa (Medicago sativa), we propose the existence of a dispersed middle repetitive element about 3400 bp long with a copy number in the range of 2-3 x 10(3) per haploid genome. The average A+T content of the sequences was 54.6%, compared with 61.4% for the alfalfa genome. Sequence homologies between overlapping regions of the clones ranged from 85 to 89.5% with an average of 86.6%; sequence divergence was due largely to single base pair changes, with deletions or insertions occurring randomly across sequences. An open reading frame (ORF) in one clone, RPE15, contained homologies to cereal prolamin genes and a legumin box was located upstream of the coding region. A Northern blot of RNA from various alfalfa tissues, probed with the above clone containing this ORF, showed an extensive heterodispersed pattern of hybridization in the late stages of flower bud development but in no other tissues.