Multiple insertions ofCOIN, a novel maize Foldback transposable element, in theConringgene cause a spontaneous progressive cell death phenotype

Similar progressive leaf lesion phenotypes, namedconringfor "concentric ring," were identified in 10 independently derived maize lines. Complementation and mapping experiments indicated that the phenotype had the same genetic basis in each line - a single recessive gene located in a 1.1-Mb region on chromosome 2. Among the 15 predicted genes in this interval, Zm00001d003866 (subsequently renamedConring or Cnr) had insertions of four related 138 bp transposable element (TE) sequences at precisely the same site in exon 4 in nine of the 10cnralleles. The 10thcnrallele had a distinct insertion of 226 bp of in exon 3. Genetic evidence suggested that the 10cnralleles were independently derived, and arose during the derivation of each line. The four TEs, namedCOINa (for COnring INsertion) throughCOINd, have not been previously characterized and consist entirely of imperfect 69-bp terminal inverted repeats characteristic of theFoldbackclass of TEs. They belong to three clades of a family of maize TEs comprising hundreds of sequences in the genome of the B73 maize line.COINelements preferentially insert at TNA sequences with a preference for C and G nucleotides in the immediately flanking 5 ' and 3 ' regions, respectively. They produce a three-base target site duplication and do not have homology to other characterized TEs. We propose thatCnris an unstable gene that is mutated insertionally at high frequency, most commonly due toCOINelement insertions at a specific site in the gene.