Paramutation phenotypes at multiple loci in <i>Mop2-1</i> plants.

a At b1, pl1 and p1 the paramutagenic and paramutable alleles are epialleles, i.e. they have exactly the same DNA sequence, but distinct expression and chromatin states. In contrast, the paramutagenic R-st and paramutable R-r alleles are structurally distinct [for a review, see [7]]. When R-r is paramutated by R-st, it is referred to as R-r'; R-r and R-r' are epialleles. b The prevention of paramutation is assayed when a paramutagenic and paramutable allele are combined in plants homozygous or heterozygous for Mop2-1. The test for release of silencing assays pigment levels when a previously paramutated (silenced) allele is exposed to heterozygous or homozygous Mop2-1. c Three sequential generations carrying P1-rr' in Mop2-1 homozygotes (40 total ears) showed no increased expression of P1-rr'. dMop2-1/+ did not release R-r' silencing previously established by R-st. Tests with homozygous Mop2-1 were inconclusive because paramutated R-r' reverted at high frequency to a highly expressed state similar to R-r regardless of the Mop2-1 genotype.