Role of AtMSH7 in UV-B-induced DNA damage recognition and recombination

Abstract

The mismatch repair (MMR) system maintains genome integrity by correcting replication-associated errors and inhibiting recombination between divergent DNA sequences. The basic features of the pathway have been highly conserved throughout evolution, although the nature and number of the proteins involved in this DNA repair system vary among organisms. Plants have an extra mismatch recognition protein, MutSγ, which is a heterodimer: MSH2-MSH7. To further understand the role of MSH7 in vivo, we present data from this protein in Arabidopsis thaliana. First, we generated transgenic plants that express β-glucuronidase (GUS) under the control of the MSH7 promoter. Histochemical staining of the transgenic plants indicated that MSH7 is preferentially expressed in proliferating tissues. Then, we identified msh7 T-DNA insertion mutants. Plants deficient in MSH7 show increased levels of UV-B-induced cyclobutane pyrimidine dimers relative to wild-type (WT) plants. Consistent with the patterns of MSH7 expression, we next analysed the role of the protein during somatic and meiotic recombination. The frequency of somatic recombination between homologous or homeologous repeats (divergence level of 1.6%) was monitored using a previously described GUS recombination reporter assay. Disruption of MSH7 has no effect on the rates of somatic homologous or homeologous recombination under control conditions or after UV-B exposure. However, the rate of meiotic recombination between two genetically linked seed-specific fluorescent markers was 97% higher in msh7 than in WT plants. Taken together, these results suggest that MSH7 is involved in UV-B-induced DNA damage recognition and in controlling meiotic recombination.

HAC1 and HAF1 Histone Acetyltransferases Have Different Roles in UV-B Responses in Arabidopsis

“…Interestingly, UV-B caused a similar CPD accumulation in all lines, including WT plants ( Figure 2 ). These results were comparable to those previously reported for HAG1 and HAG2 deficient plants and WT plants from the Col-0 and Ws lines (Campi et al, 2012; Lario et al, 2015; Fina and Casati, 2015); but differed to what was determined for ham and hag3 mutants (Campi et al, 2012; Fina and Casati, 2015). Because it is possible that subtle effects of HAF or HAC activity on CPD removal might be masked by photolyase activity, the UV-B treatments were repeated in the absence of white light that allow photorepair.…”

“…It is interesting to note that only very high UV-B levels have been reported to induce oxidative damage in DNA (see Britt, 1996); while UV-B levels used in our study are similar to those in natural sunlight (Casati and Walbot, 2003). We showed that our UV-B treatment has no effect on the rates of somatic homologous or homeologous recombination, demonstrating that no strand break occurs after exposure (Lario et al, 2015). On the contrary, mitomycin C is a DNA cross-linking agent which damage is mostly repaired by homologous recombination (HR; Bleuyard et al, 2005).…”

The genome of an Encephalitozoon cuniculi type III strain reveals insights into the genetic diversity and mode of reproduction of a ubiquitous vertebrate pathogen

“…A priori, this suggests that ECIII-L (and to certain extent, also other species that potentially lack portions of Spo11, such as the Mitosporidium daphnia, Rozella allomycis and Nosema bombycis, Figure 5) may not be capable of sexual reproduction and that genome homogenization in this strain (and possibly all strains) must be driven by asexual mechanisms. One of these could be mitotic recombination, as this known asexual driver of genome homogenization in many microbial eukaryotes, including many pathogens (Butler et al, 2009;Cuomo et al, 2012;Rosenblum et al, 2013), has been shown to increase in frequency in the absence of a functional Spo11 (Lario et al, 2015;Sun and Heitman, 2015). As a sexual alternative, ECIII-L could undergo meiosis without the need for Spo11, a situation that would be analogous to what is seen in the distant microbial lineage Dyctiostelium sp (Goodenough and Heitman, 2014), or perhaps, the SNP we identified is too recent to have impacted the genome of ECIII-L in significant ways (that is, EcIII-L has always been a 'selfer', and the recent Spo11 mutation we found will only affect the mutational patterns of ECIII-L down the road).…”

MutS-Homolog2silencing generates tetraploid meiocytes in tomato (Solanum lycopersicum)

“…The expression of MSH7 is required for wild-type level of fertility in barley (Lloyd et al ., 2007). MSH7 also plays a role in UV-B-induced DNA damage recognition and recombination in Arabidopsis (Lario et al ., 2015).…”

“…Among the interacting partners for MSH2; mutants are reported only for MSH6 and MSH7 in Arabidopsis. The msh6 mutant does not display a visible phenotype (Lario et al ., 2011) however, msh7 mutant shows an increase in meiotic recombination frequency (Lario et al ., 2015). The role of MSH7 in meiotic recombination is also reported in tomato, where RNAi silencing of MSH7 improves homeologous meiotic recombination with a chromosome from S. lycopersicoides (Tam et al ., 2011).…”