Involvement of DnaE, the second replicative DNA polymerase from Bacillus subtilis, in DNA mutagenesis

In a large group of organisms including low G + C bacteria and eukaryotic cells, DNA synthesis at the replication fork strictly requires two distinct replicative DNA polymerases. These are designated pol C and DnaE in Bacillus subtilis. We recently proposed that DnaE might be preferentially involved in lagging strand synthesis, whereas pol C would mainly carry out leading strand synthesis. The biochemical analysis of DnaE reported here is consistent with its postulated function, as it is a highly potent enzyme, replicating as fast as 240 nucleotides/s, and stalling for more than 30 s when encountering annealed 5'-DNA end. DnaE is devoid of 3' --> 5'-proofreading exonuclease activity and has a low processivity (1-75 nucleotides), suggesting that it requires additional factors to fulfill its role in replication. Interestingly, we found that (i) DnaE is SOS-inducible; (ii) variation in DnaE or pol C concentration has no effect on spontaneous mutagenesis; (iii) depletion of pol C or DnaE prevents UV-induced mutagenesis; and (iv) purified DnaE has a rather relaxed active site as it can bypass lesions that generally block other replicative polymerases. These results suggest that DnaE and possibly pol C have a function in DNA repair/mutagenesis, in addition to their role in DNA replication

Integrated miRNA and transcriptome profiling to explore the molecular determinism of convergent adaptation to corn in two lepidopteran pests of agriculture

BackgroundThe degree to which adaptation to same environment is determined by similar molecular mechanisms, is a topic of broad interest in evolutionary biology, as an indicator of evolutionary predictability. We wished to address if adaptation to the same host plant in phytophagous insects involved related gene expression patterns. We compared sRNA-Seq and RNA-Seq data between two pairs of taxa of Ostrinia and Spodoptera frugiperda sharing maize as host-plant. For the latter, we had previously carried out a reciprocal transplant experiment by feeding of the larvae of the Corn strain (Sf-C) and the Rice strain (Sf-R) on corn versus rice and characterized the mRNA and miRNA responses.ResultsFirst, we predicted the genes encoding miRNA in Ostrinia nubilalis (On) and O. scapulalis (Os). Respectively 67 and 65 known miRNA genes, as well as 196 and 190 novel ones were predicted with Os genome using sncRNAs extracted from whole larvae feeding on corn or mugwort. In On, a read counts analysis showed that 37 (55.22%) known miRNAs and 19 (9.84%) novel miRNAs were differentially expressed (DE) on mugwort compared to corn (in Os, 25 known miRs (38.46%) and 8 novel ones (4.34%)). Between species on corn, 8 (12.5%) known miRNAs and 8 (6.83%) novel ones were DE while only one novel miRNA showed expression variation between species on mugwort. Gene target prediction led to the identification of 2953 unique target genes in On and 2719 in Os, among which 11.6% (344) were DE when comparing species on corn. 1.8% (54) of On miR targets showed expression variation upon a change of host-plant.We found molecular changes matching convergent phenotype, i.e., a set of nine miRNAs that are regulated either according to the host-plant both in On and Sf-C or between them on the same plant, corn. Among DE miR target genes between taxa, 13.7% shared exactly the same annotation between the two pairs of taxa and had function related to insect host-plant interaction.ConclusionThere is some similarity in underlying genetic mechanisms of convergent evolution of two distant Lepidopteran species having adopted corn in their host range, highlighting possible adaptation genes

Global FAW population genomic signature supports complex introduction events across the 1 Old World 2 3

16 Accurate genomic knowledge can elucidate the global spread patterns of invasive pests. The high-17 profile invasive agricultural pest Spodoptera frugiperda (fall armyworm; FAW) is a case in point. Native to the 18 Americas, the FAW was first reported in West Africa in 2016 and has rapidly spread to over 64 countries across 19 the Old World, resulting in significant economic losses. The chronological order of reported detections has led 20 to the hypothesis that the FAW moved eastwards across Africa and then Asia, however genomic evidence 21 remains lacking to test this hypothesis and to identify the potential origin of invasive populations. Using a whole 22 genome sequencing approach, we explored the population genomic signatures of FAW populations from the 23 Americas and the Old World. Analyses of complete mitochondrial DNA genomes identified 12 maternal lineages 24 across the invasive range, while genomic signatures from 870 high-quality nuclear genome-wide single 25 nucleotide polymorphic (SNP) DNA markers identified five distinct New World populations that broadly reflected 26 their native geographical ranges and absence of host-plant preference status. Unique FAW populations in the 27 Old World were also identified that suggested multiple introductions underpinned their rapid global spread. We 28 identified in Asian FAW individuals, genomes lacking evidence of admixture; while analysis of identified complex 29 substructure revealed significant directional geneflow from Asia into East Africa, in contrast to a simple east-to-30 west spread. Our study highlights the need for population genomics approaches in analysing complex pest 31 invasions, and the importance of international partnership to address global biosecurity challenges presented 32 by emerging high priority insect pests. 33 34 35 3