GENETIC-CHARACTERIZATION OF ACT1, THE ACTIVATOR OF A NONAUTONOMOUS TRANSPOSABLE ELEMENT FROM PETUNIA-HYBRIDA

The line W138 of Petunia hybrida has variegated flowers because it is homozygous for the mutable an1-W138 allele. Excision of the element, c ausing instability, depends on the presence of the activator Act1. The previously characterised non-autonomous element dTph1 excises from th e dfrC gene in response to Act1. This implies that both non-autonomous elements belong to the same transposable element family. In a range o f distantly related cultivars we could detect a single functional Act1 element. Linkage analysis for 11 of these lines showed that Act1 was Located on chromosome I in all cases, indicating that the element migh t be fixed in the genome. A group of cultivars that did not exhibit Ac t1 activity could be traced back to a recent common origin ('Rose of H eaven'). Cultivars within this group presumably harbour the same inact ivated Act1 element. Among the lines tested were 7 lines representing the two species (P. axillaris and P. integrifolia) from which P. hybri da originated. None of these exhibited Act1 activity. We assume that A ct1 is present in an inactive state in these Lines and that it was act ivated upon interspecific crossing. In general, lines representing the two parental species and P. hybrida cultivars contain between 5 and 2 5 dTph1 elements. The lines R27 and W138, however, contain significant ly more dTph1 elements (> 50) than all other lines.