The Cy responsive bz-rcy receptor (Schnable and Peterson, MGN 58:9) is not triggered to produce spots by any of the following regulatory elements: Ac, Bg, c2-m3, Dt, En, Fcu, Mrh, Mut, Uq. Similarly, Cy does not trigger mutability at Ac, Bg, Dt, En, Fcu, Mrh, Mut, or Uq responsive alleles. These data are summarized in Table 1.
Tests of Cy versus Robertson's Mutator place Cy as a newly described system subject to a negative relationship to Robertson's Mutator. In order to test this relationship five plants from Mutator stocks homozygous for bz-o were assayed for Cy content by crosses to bz-rcy/bz-o (cross 1). Simultaneously, these plants were tested for Mutator activity via Robertson's seedling test. These results are shown in Table 2. These data can not rule out the possibility that bz-rcy responds to the same transposable element responsible for Robertson's Mutator phenomena (Mu1).
The appearance of Cy in Mutator stocks (Table 2) is in itself of interest as Cy had not previously been observed in stocks unrelated to bz-rcy (see, however, Scheffler and Peterson MGN 59 and the following note). The pedigree of the population (1963 1005/828) from which bz-rcy arose (Schnable and Peterson, MGN 58:9) has been traced back to 1952. It has never been crossed by Mutator stocks. Plants derived from Mutator stocks which displayed Cy activity in cross 1 contain many Cy elements based on the segregation ratios of spotted bronze:not spotted bronze.
The presence of many genetically active Cy in Mutator stocks is consistent with the hypothesis that bz-rcy is responding to the element responsible for the Mutator phenomena, which must be present in high copy numbers. Tests are currently underway to assay Cy stocks for the presence of Mu1 homologous sequences.
Patrick S. Schnable and Peter A. Peterson
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