Mol Gen Genet (1989) 215:317-321 MGG © Springer-Verlag 1989 Genetic evidence of a relationship between two maize transposable element systems: Cy and Mutator Patrick S. Schnable* and Peter A. Peterson Department of Agronomy, Iowa State University, Ames, IA 50011, USA Summary. The Cy transposable element system is composed of two genetically defined elements: an rcy receptor element inserted at the Bronze-1 locus; and an independently segre- gating regulatory element, Cy. The Cy system is not func- tionally homologous to any of the non-Mutator transpos- able element systems. Evidence is presented that supports a relationship between the Cy system and the family of Mul-homologous transposable elements that are responsi- ble for the Mutator phenomenon. Although related, Cy ele- ments and the Mul-homologous elements are not identical; Cy is inherited in a near-Mendelian fashion, in contrast to the non-Mendelian inheritance of the Mul-homologous elements. Key words: Transposon - Mul - rcy : Mu7 bz-rey - TEL population Introduction Ten transposable element families have been characterized at the genetic level in maize. Most are composed of two classes of elements, non-autonomous receptors, such as Ds or I, and regulatory elements, such as Ac or En, which are autonomously transposition competent (Fedoroff 1983; Freeling 1984; Nevers et al. 1985; Peterson 1987). The spe- cific interactions among the members of these two classes of elements define systems (Peterson 1981). Descriptions of the discovery and characteristics of three of the better characterized systems have been reviewed (Fedoroff 1983; Freeling 1984; Peterson 1987; Nevers et al. 1985). Systems not extensively reviewed in these articles have been de- scribed by Gonella and Peterson (Fcu; 1977, 1978), Sala- mini (Bg; 1980, 1981), Friedemann and Peterson (Uq; 1982), Rhoades and Dempsey (Mrh and Mut; 1982, 1983), Peterson (c2-m3; 1984) and B. McClintock (c2-m3; per- sonal communication). In common with eight of the ten systems, the Cy system is composed of two classes of elements: the rcy receptor element, which, in the bz-rcy allele, resides at the Bz locus; and independently segregating Cy (Cycler) regulatory ele- ments, each of which is inherited as a near-Mendelian unit. The insertion of the rcy element into Bz interrupted Bz * Present address: Department of Genetics, Iowa State University, Ames, IA 50011, USA Offprint requests to: P.S. Schnable gene function and generated the bz-rcy alMe. In theabsence of a Cy element, rcy cannot excise from bz-rcy. Hence, in the absence of Cy, bz-rcy conditions a stable bronze aleurone. However, in the presence of a Cy element, rcy can excise. These excisions generally restore bz-rcy to Bz function. Therefore, in the presence of Cy, bz-rcy conditions a spotted aleurone. To date, unlike most of the transposable element sys- tems of maize, the Mutator phenomenon and the Mu ele- ments, which are responsible for the Mutator phenomenon (Bennetzen 1985), have not been resolved into regulatory and receptor elements by either genetic or molecular tests. The Mutator phenomenon and the Mu elements are inher- ited in a non-Mendelian fashion (Robertson 1978, 1983). Although Mu elements are found in highest copy numbers in Mutator lines, they are also present in non-Mutator lines, but at reduced copy numbers (Chandler et al. 1986). The family of Mu elements contains members of several sizes, two of which, the 1.4 kb and the 1.7 kb elements, have been shown to transpose (Taylor et al. 1986). Examples of the 1.4 kb and 1.7 kb elements have been cloned (Bennetzen et al. 1984; Taylor et al. 1986) and sequenced (Barker et al. 1984; Taylor and Walbot 1988). In this paper, we will present genetic evidence that sup- ports a relationship between the Cy system and Mutator. Materials and methods Source of genetic materials. The bz-rcy allele was isolated from a population (TEL) unrelated to Mutator stocks, al- though both the TEL population and Mutator contain W23 germplasm (Schnable and Peterson 1986). Mutator stocks were provided by D. Robertson, Iowa State University. Rationale of the genetic tests A. Test of Cy against receptor elements of the established systems and of bz-rcy against the regulatory elements of the established systems. Depending on the system involved, one of three testing strategies was used. These strategies are similar to those employed by Friedemann and Peterson (1982). Detailed crossing protocols are provided by Schna- ble (1986). In the test of Cy, individual plants were scored for Cy activity and for the presence of the appropriate regu- latory element. If it could be shown that at least one plant exhibited Cy activity, but lacked the regulatory element under study, it was possible to state that Cy does not trigger