Kasbekar, D.P. (2013) Neurospora Duplications, and Genome Defense by RIP and Meiotic Silencing [Chapter 7]. In: Neurospora: Genomics and Molecular Biology. McCluskey Caister Academic Press, Norfolk, UK, pp. 109-127. ISBN 978-1-908230-12-6

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Abstract

Repeat-induced point mutation (RIP) and meiotic silencing by unpaired DNA serve to prevent the accumulation of transposable elements and other repetitive DNA in the Neurospora genome. RIP occurs in the premeiotic dikaryon that forms following fertilization in a sexual cross, and induces G:C to A:T mutations in duplicated DNA, thus destroying any ORFs present in it. Meiotic silencing uses RNAi to eliminate transcripts of genes that do not pair properly in meiosis with a homologue in the same chromosomal location and thus silences them and even their homologous genes at other chromosomal locations, regardless of whether or not the latter are paired. Chromosome segment duplications (Dps) also are substrates for RIP. But RIP is less severe in Dp-borne genes than in small gene-sized duplications, and the presence ofDps in a cross can lower the efficiency of RIP in small duplications. Dps thus behave as dominant suppressors of RIP. Short Dps (i.e., < 200 kbp) that individually are unable to suppress RIP can nonetheless do so in multiply heterozygous crosses if the total amount of duplicated DNA exceeds ~300 kbp. This suggests that RIP suppression by Dps might occur via titration of the RIP machinery. Dp-heterozygous crosses are barren, but their productivity can be increased by suppression of meiotic silencing. Barrenness limits the vertical transmission of Dps, therefore meiotic silencing augments genome defense by RIP, but it might also protect the genome independently of RIP. Meiotic silencing is demonstrable using tester strains that silence genes whose silencing can produce striking ascus-development phenotypes. Crosses of the testers with many wild-isolated strains revealed meiotic silencing to be relatively weak and restricted only to the early perithecia of the cross. We hypothesize that genes essential for meiotic silencing might become unpaired with time, possibly aided by sequence polymorphisms between the tester and wild genomes, thus becoming self-silenced, and thereby shorten the duration of silencing. Some wild strains contain genetic factors that when brought together produce a synthetic RIP suppressor phenotype. These factors might represent sub-threshold sized and cryptic Dps

Item Type:	Book Section
Depositing User:	Users 2 not found.
Date Deposited:	15 Sep 2015 06:27
Last Modified:	15 Sep 2015 06:27
URI:	http://cdfd.sciencecentral.in/id/eprint/512

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