The structure and paramutagenicity of the R-marbled haplotype of Zea mays

Paramutation is the meiotically heritable silencing of a gene that can occu r in particular heterozygous combinations. The R-marbled (R-mb) haplotype i s paramutagenic: it causes paramutable r1 haplotypes like R-r to become her itably silenced. R-mb was found to comprise three distinct r1 genes arrange d as direct repeats. The most distal gene of R-mb, Scm, contains a novel tr ansposable element, Shooter (Sho). Excision of the Sho element early in ale urone development results in the characteristic "marbled" aleurone pigmenta tion pattern conferred by R-mb. The effect of gene copy number on the param utagenic strength of R-mb was tested. Paramutagenic strength of R-mb is dir ectly correlated with r1 gene copy number. Paramutagenic strength of R-mb i s directly correlated with r1 gene copy number. Paramutagenic strength of R -mb was not affected by removal, through crossing over, of the Sho transpos on. Finally, R-mb does not appear to contain the transposable element, Dopp ia, which is associated with paramutability of R-r, and has been suggested to play a role in paramutagenicity of another paramutagenic haplotype, R-st ippled.