An En (Spm) -system insertion partly reduces the color-suppressing potency of the dominant C-I allele in maize.

Two mutable C-I alleles, C-Im857059 and C-Im857062 of the Enhancer-Inhibitor (En-I) or Suppressormutator (Spm) transposable-element system, were shown to express a sectored phenotype (colorless sectors on a colored background). This sectoring is a consequence of an I receptor element at the C-I allele responding to an independently segregating, transactive En element. The I element insertion results in the partial reduction of the suppressive potency of the normal C-I alleles. A wide range of suppressive potencies of these two C-Im(r) alleles was found when tested against other C alleles, including C-S and C. Though each of the C-Im(r) alleles has a standard I element, there is a significant difference in the suppressive potencies of the two C-Im(r) alleles, which possibly indicates a different position of the I insert in the coding region affecting the C-I transcript.