Chromosome Segment Duplications in Neurospora crassa and Their Effects on Repeat-Induced Point Mutation and Meiotic Silencing by Unpaired DNA

摘要

The size and extent of four Neurospora crassa duplications, Dp(AR17) , Dp(IBj5) , Dp(OY329) , and Dp(B362i) , was determined by testing the coverage of RFLP markers. The first three duplications were all ～350 kb and have been shown in earlier studies to act as dominant suppressors of repeat-induced point mutation (RIP) in gene-sized duplications, possibly via titration of the RIP machinery. Dp(B362i) , which is only ～117 kb long, failed to suppress RIP. RIP suppression in gene-sized duplications by large duplications was demonstrated using another test gene, dow , and supposedly applies generally. Crosses homozygous for Dp(AR17) or Dp(IBj5) were as barren as heterozygous crosses. Barrenness of the heterozygous but not the homozygous crosses was suppressible by Sad-1 , a semidominant suppressor of RNAi-dependent meiotic silencing by unpaired DNA. A model is proposed in which large duplications recessively suppress semidominant Sad-1 mutations. The wild-isolated Sugartown strain is hypothesized to contain a duplication that confers not only dominant suppression of RIP but also a barren phenotype, which is linked (9%) to supercontig 7.118 in LG VII.