A DISPERSED FAMILY OF REPETITIVE DNA-SEQUENCES EXHIBITS CHARACTERISTICS OF A TRANSPOSABLE ELEMENT IN THE GENUS LYCOPERSICON

A segment of DNA 5' to the transcribed region of an auxin-regulated ge ne, ARPI, from Lycopersicon esculentum Mill. cv. VFN8 contains a seque nce with the structural characteristics of a transposable element. The putative element (Lyt1) is 1340 bp long, has terminal inverted repeat s of approximately 235 bp and is flanked by 9-bp direct repeats. Lyt1 has a structure similar to the Robertson's Mutator (Mu) family from ma ize. The terminal inverted repeats are 80% AT-rich, are 96.6% identica l, and define a larger family of repetitive elements. Southern analysi s and genomic dot-blot reconstructions detected at least 41 copies of Lyt1-hybridizing sequences in red-fruited Lycopersicon spp. (L. escule ntum, L. pimpinelliolium and L. cheesmanii), and 2-8 copies in the gre en-fruited species (L. hirsutum, L. pennellii, L. peruvianum, L. chile nse and L. chmielewskii). There were two to four copies in the Solanum spp. closely allied with the genus Lycopersicon (S. lycopersicoides, S. ochranthum and S. juglandifolium), while the more distantly related Solanum spp. showed little (one to two copies in S. tuberosum) to no (S. quitoense) detectable hybridization under stringent conditions. Li nkage analysis in the F-2 progeny of a cross between L. esculentum and L. cheesmanii indicated that at least six loci thar hybridize to the Lyt1 sequence are dispersed in the genome. Polymerase chain reaction a nd Southern analyses revealed that some red-fruited accessions and L. chmielewskii lacked Lyt1 5' to the transcribed region of ARPI. Subsequ ent sequence analysis indicated that only one copy of the 9-bp direct repeat (target site) was present, suggesting that transposition of the element into the ARPI gene occurred after the divergence of the red-f ruited and green-fruited Lycopersicon species.