Rj. Young et al., A DISPERSED FAMILY OF REPETITIVE DNA-SEQUENCES EXHIBITS CHARACTERISTICS OF A TRANSPOSABLE ELEMENT IN THE GENUS LYCOPERSICON, Genetics, 137(2), 1994, pp. 581-588
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.