The unilateral appearance of the effect of a modifier in the enhancer/suppressor-mutator (En/Spm) system in maize: Female expression

Modifiers in the En/Spm system in maize have previously been described to affect either the timing or frequency of mutation events of several autonomous and nonautonomous alleles. In this study we describe another serendipitously discovered Modifier (Mdf), with the advantage of reciprocal crosses, that mediates to increase the mutability of an En/Spm responsive allele a1-m(r). Interestingly, in reciprocal crosses the Mdf effect is observed only when Mdf is transmitted by the female side of the cross. This unilateral appearance of the Mdf effect is accounted for by the two-to-one interaction hypothesis, in which at least two copies of Mdf and at least one copy of En/Spm are required in the endosperm for the manifestation of the Mdf effect.