PLoS Genet

To generate highly specific and adapted immune responses, B cells diversify their antibody repertoire through mechanisms involving the generation of programmed DNA damage. Somatic hypermutation (SHM) and class switch recombination (CSR) are initiated by the recruitment of activation-induced cytidine deaminase (AID) to immunoglobulin loci and by the subsequent generation of DNA lesions, which are differentially processed to mutations during SHM or to double-stranded DNA break intermediates during CSR. The latter activate the DNA damage response and mobilize multiple DNA repair factors, including Parp1 and Parp2, to promote DNA repair and long-range recombination. We examined the contribution of Parp3 in CSR and SHM. We find that deficiency in Parp3 results in enhanced CSR, while SHM remains unaffected. Mechanistically, this is due to increased occupancy of AID at the donor (Smu) switch region. We also find evidence of increased levels of DNA damage at switch region junctions and a bias towards alternative end joining in the absence of Parp3. We propose that Parp3 plays a CSR-specific role by controlling AID levels at switch regions during CSR

Does mycorrhization influence herbivore-induced volatile emission in Medicago truncatula?

Symbiosis with mycorrhizal fungi substantially impacts secondary metabolism and defensive traits of colonised plants. In the present study, we investigated the influence of mycorrhization (Glomus intraradices) on inducible indirect defences against herbivores using the model legume Medicago truncatula. Volatile emission by mycorrhizal and non-mycorrhizal plants was measured in reaction to damage inflicted by Spodoptera spp. and compared to the basal levels of volatile emission by plants of two different cultivars. Emitted volatiles were recorded using closed-loop stripping and gas chromatography/mass spectrometry. The documented volatile patterns were evaluated using multidimensional scaling to visualise patterns and stepwise linear discriminant analysis to distinguish volatile blends of plants with distinct physiological status and genetic background. Volatile blends emitted by different cultivars of M. truncatula prove to be clearly distinct, whereas mycorrhization only slightly influenced herbivore-induced volatile emissions. Still, the observed differences were sufficient to create classification rules to distinguish mycorrhizal and non-mycorrhizal plants by the volatiles emitted. Moreover, the effect of mycorrhization turned out to be opposed in the two cultivars examined. Root symbionts thus seem to alter indirect inducible defences of M. truncatula against insect herbivores. The impact of this effect strongly depends on the genetic background of the plant and, hence, in part explains the highly contradictory results on tripartite interactions gathered to date

Expression of the PR-b1" gene in the roots of two Nicotiana species and their amphidiploid hybrid infected with virulent and avirulent races of Chalara elegans

The expression levels of PR-b1'' gene coding for PR-b1'' protein (a PR-I group protein) were investigated in the roots of two Nicotiana species and their amphidiploid hybrid in response to infection by virulent (84-1) or avirulent (85-26) races of black root rot fungus Chalara elegans. Nicotiana glutinosa is susceptible to C. elegans, while Nicotiana debneyi and the amphidiploid hybrid N. glutinosa x N. debneyi are highly resistant. The results showed that irrespective of whether the plant is susceptible or resistant, and the fungal race virulent or avirulent, low infection rates induce low levels of PR-b1'' mRNA, and high infection rates result in high production of PR-b1'' mRNA. The amphidiploid hybrid, which expresses the protein PR-b1'' constitutively, showed similar PR-b1'' mRNA levels with both races of C. elegans. At maximal levels of accumulation, PR-b1'' mRNA is quantitatively similar in the two Nicotiana species, and the amphidiploid hybrid, whatever the nature of the inoculum

Functional analysis of the membrane proteome of Medicago truncatula roots upon colonization by the arbuscular mycorrhizal fungus Glomus irregulare

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