Originally published as Genetics Published Articles Ahead of Print on December 15, 2005.

Genetics, Vol. 172, 1511-1519, March 2006, Copyright © 2006
doi:10.1534/genetics.105.050468

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

Meenal Vyas, C. Ravindran and Durgadas P. Kasbekar1

Centre for Cellular and Molecular Biology, Hyderabad 500 007, India

1 Corresponding author: Centre for Cellular and Molecular Biology, Uppal Rd., Hyderabad 500 007, India.
E-mail: kas{at}ccmb.res.in

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.




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