9604919 Eggleston The R-marbled (R-mb) complex of r genes in maize exemplifies many features of epigenetic gene silencing in plants. First, kernel pigmentation is inhibited irregularly in a pattern characteristic of transposable element action. Germinal revertants confer strong seed and scutellum color and weak scutellar node color. Unique among r alleles, in combination with dominant alleles of the a3 and pl loci, this allele permits variegated anthocyanin expression in anthers. Even more remarkably, heterozygosity between R-mb and certain other r alleles on the homologous chromosome leads to heritable inactivation of the latter (paramutation). No change in R-mb is observed. Genetic linkage of Lc, a displaced copy of r not normally sensitive to paramutation, to R-mb leads to a gradual suppression of Lc expression. Questions to be addressed in this proposal include: How are the determinants of cis and trans gene silencing in R-mb organized and are they related? Is expression of gene sin R-mb itself suppressed by these determinants? What types of molecular/genetic changes alter the potential for silencing? To study those questions, the R-mb complex will be fractionated by intralocus recombination and the products analyzed by a of genetic and molecular methods. Results from this work will lead t a better understanding of mechanisms of gene silencing and evolutionary forces affecting duplicated sequences in plants and other species. The results also will elucidate some epigenetic, or non-Mendelian effects to be expected, and avoided or enhanced, during the use of transgenes in basic research and in crop and animal improvement.
