A Modified Autonomous En Transposon in Maize (Zea mays L.) Elicits a Differential Response of Reporter Alleles

Transposable elements in maize are composed of a defined molecular structure that includes coding sequences, determiners of functionality and ordered terminal motifs that provide binding sites for transposase proteins. Alterations in these components change the phenotypic expression of unstable genes with transposon inserts. The molecular basis for the altered timing and frequency of transposition as determined by the size and number of spots on kernels or stripes on leaves has generally been described for defective inserts in genes. Most differential patterns can be ascribed to alterations in the terminal motifs of the reporter allele structure that supplies a substrate (terminal inverted repeat motifs) for transposase activity. For autonomously functioning alleles, the explanations for changes in phenotype are not so clear. In this report, an En-related element identified as F-En is described that shares with En the recognition of a specific defective element c1(mr)888104 but differs from En in that this F-En element does not recognize the canonical c1(mr) elements that are recognized by En. Evidence is provided suggesting that F-En does not recognize other En/Spm-related defective elements, some of whose sequences are known. This modified En arose from a c1-m autonomously mutating En allele.