SummaryThe DNA damage response and DNA recombination are two interrelated mechanisms involved in maintaining the integrity of the genome, but in plants they are poorly understood. RecQ is a family of genes with conserved roles in the regulation of DNA recombination in eukaryotes; there are seven members in Arabidopsis. Here we report on the functional analysis of the Arabidopsis RecQl4A gene. Ectopic expression of Arabidopsis RecQl4A in yeast RecQ-deficient cells suppressed their hypersensitivity to the DNA-damaging drug methyl methanesulfonate (MMS) and enhanced their rate of homologous recombination (HR). Analysis of three recQl4A mutant alleles revealed no obvious developmental defects or telomere deregulation in plants grown under standard growth conditions. Compared with wild-type Arabidopsis, the recQl4A mutant seedlings were found to be hypersensitive to UV light and MMS, and more resistant to mitomycin C. The average frequency of intrachromosomal HR in recQl4A mutant plants was increased 7.5-fold over that observed in wild-type plants. The data reveal roles for Arabidopsis RecQl4A in maintenance of genome stability by modulation of the DNA damage response and suppression of HR.

Nanoparticles have gained significant attention in recent years due to their numerous applications in various aspects of human life. A variety of methods have been investigated for synthesis of nanoparticles among which, biogenic approaches are considered as both simple and ecofriendly. Here, a new single-step biological approach was employed for synthesis of silver chloride nanoparticles (AgCl-NPs) at room temperature, using walnut green husk extract. Macromolecules present in the plant extract, which might act as bio-reductants and/or stabilisers of nanoparticles were characterised by Fourier transform Infrared spectroscopy. X-ray diffraction pattern and transmission electron microscopy revealed that 1 mM of AgNO3 produced mostly spherical nanoparticles in a range of 4À30 nm in diameter with an average of 16 nm. Interestingly, the synthesised nanoparticles showed significant inhibitory effects against Escherichia coli and Staphylococcus aureus clinical isolates. Altogether, these data suggest a new encouraging application of a medicinal plant bound with synthesised AgCl nanoparticles.

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