On a role

The genomic integrity of every organism is constantly challenged by endogenous and exogenous DNA-damaging factors. Mutagenic agents cause reduced stability of plant genome and have a deleterious effect on development, and in the case of crop species lead to yield reduction. It is crucial for all organisms, including plants, to develop efficient mechanisms for maintenance of the genome integrity. DNA repair processes have been characterized in bacterial, fungal, and mammalian model systems. The description of these processes in plants, in contrast, was initiated relatively recently and has been focused largely on the model plant Arabidopsis thaliana. Consequently, our knowledge about DNA repair in plant genomes - particularly in the genomes of crop plants - is by far more limited. However, the relatively small size of the Arabidopsis genome, its rapid life cycle and availability of various transformation methods make this species an attractive model for the study of eukaryotic DNA repair mechanisms and mutagenesis. Moreover, abnormalities in DNA repair which proved to be lethal for animal models are tolerated in plant genomes, although sensitivity to DNA damaging agents is retained. Due to the high conservation of DNA repair processes and factors mediating them among eukaryotes, genes and proteins that have been identified in model species may serve to identify homologous sequences in other species, including crop plants, in which these mechanisms are poorly understood. Crop breeding programs have provided remarkable advances in food quality and yield over the last century. Although the human population is predicted to "peak" by 2050, further advances in yield will be required to feed this population. Breeding requires genetic diversity. The biological impact of any mutagenic agent used for the creation of genetic diversity depends on the chemical nature of the induced lesions and on the efficiency and accuracy of their repair. More recent targeted mutagenesis procedures also depend on host repair processes, with different pathways yielding different products. Enhanced understanding of DNA repair processes in plants will inform and accelerate the engineering of crop genomes via both traditional and targeted approaches.

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DNA damage and repair in plants - from models to crops.

Melatonin and calcium function synergistically to promote the resilience through ROS metabolism under arsenic-induced stress

Mutagenesis is a molecular mechanism that deliberately creates specific alterations in the nucleotide or amino acid sequence of a DNA or protein molecule. It is employed to determine the biological structural and functional activity of macromolecules such as proteins and nucleic acids. Such position specific alteration in a target protein or DNA sequence either by means of insertion, deletion or substitution of a specific base pair aimed to produce single or multiple point mutations is termed sitedirected mutagenesis[1].Site-directed mutagenesis is the fundamental basis of genetic modifications of DNA sequences .it helps to introduce precise genetic variations at specific sites in a PCR based process and the mutant construct is then cloned into the desirable vector system [2].

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Site-Directed Mutagenesis

Exposure of plants and animals to ultraviolet-B radiation (UV-B; 280–315 nm) is modified by stratospheric ozone dynamics and climate change. Even though stabilisation and projected recovery of stratospheric ozone is expected to curtail future increases in UV-B radiation at the Earth's surface, on-going changes in climate are increasingly exposing plants and animals to novel combinations of UV-B radiation and other climate change factors (e.g., ultraviolet-A and visible radiation, water availability, temperature and elevated carbon dioxide). Climate change is also shifting vegetation cover, geographic ranges of species, and seasonal timing of development, which further modifies exposure to UV-B radiation. Since our last assessment, there has been increased understanding of the underlying mechanisms by which plants perceive UV-B radiation, eliciting changes in growth, development and tolerances of abiotic and biotic factors. However, major questions remain on how UV-B radiation is interacting with other climate change factors to modify the production and quality of crops, as well as important ecosystem processes such as plant and animal competition, pest–pathogen interactions, and the decomposition of dead plant matter (litter). In addition, stratospheric ozone depletion is directly contributing to climate change in the southern hemisphere, such that terrestrial ecosystems in this region are being exposed to altered patterns of precipitation, temperature and fire regimes as well as UV-B radiation. These ozone-driven changes in climate have been implicated in both increases and reductions in the growth, survival and reproduction of plants and animals in Antarctica, South America and New Zealand. In this assessment, we summarise advances in our knowledge of these and other linkages and effects, and identify uncertainties and knowledge gaps that limit our ability to fully evaluate the ecological consequences of these environmental changes on terrestrial ecosystems.

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Linkages between stratospheric ozone, UV radiation and climate change and their implications for terrestrial ecosystems

Ability of barley ribosomal genes to cope with damage produced in vivo by the radiomimetic agent bleomycin was investigated. Repair kinetics of bleomycin-induced double-strand breaks in ribosomal and total genomic DNA was compared. Induction and repair of double-strand breaks in defined regions of the ribosomal genes was also analyzed. Preferential sensitivity of barley linker DNA towards bleomycin treatment in vivo was established. Relatively higher yield of initially induced double-strand breaks in genomic DNA in comparison to ribosomal DNA was also found. Fragments containing intergenic spacers of barley rRNA genes displayed higher sensitivity to bleomycin than the coding sequences. No heterogeneity in the repair of DSB between transcribed and non-transcribed regions of ribosomal genes was detected. Data indicate that DSB repair in barley rDNA, although more efficient than in genomic DNA, does not corelate with the activity of nucleolus organizer regions.

Efficient repair of bleomycin-induced double-strand breaks in barley ribosomal genes.

The potential of cytologically reconstructed barley line D-2946 to cope with the major lesions that hamper genome integrity, namely DNA single- and double-strand breaks was investigated. Strand breaks induced by γ-rays and Li ions were assessed by neutral and alkaline comet assay. Repair capacity after bleomycin treatment was evaluated by agarose gel electrophoresis under neutral and alkaline conditions. Frequencies of radiation-induced chromosome aberrations were also determined. Results indicate that radiation-mediated constitutive rearrangement of the chromosome complement has led to a substantial modulation of the sensitivity of barley genome towards DNA strand breaks, produced by ionising radiation, Li ion implantation and bleomycin in an agent-specific manner, as well as of the clastogenic response to γ-rays. Based on these findings, reconstructed barley karyotype D-2946 can be considered a candidate radio-sensitive line with reduced ability to maintain genome integrity with respect to both DNA and chromosomal damage.

Karyotype reconstruction modulates the sensitivity of barley genome to radiation-induced DNA and chromosomal damage

http://bio21.bas.bg/ippg/bg/wp-content/uploads/2012/01/abstr_l-stoilov_part-1.pdf

Induction and recovery of double-strand breaks in barley ribosomal DNA

Colletotrichum coccodes has been recognized as one of the causal agents of
 pepper fruit anthracnose in Bulgaria. Recently, this species has been
 recorded in pepper fruits in Macedonia. In Bulgaria, the fungus has also been
 isolated from roots of premature senescent pepper plants but in Macedonia it
 has not been isolated yet. The purpose of the investigation was to make
 comparative morphological, cultural and molecular characterization of C.
 coccodes isolates obtained from pepper fruits and roots in Bulgaria and
 Macedonia. Additionally, a technique was applied to differentiate among the
 C. coccodes isolates obtained from roots and other microsclerotia-producing
 fungi. On the host tissue, C. coccodes developed acervular conidiomata with
 cup-shaped fruiting bodies accompanied with dark-pigmented, unbranched,
 thick-walled sterile hyphae called setae. A slimy mass of hyaline, straight,
 unicellular, fusiform conidia appeared on nutrient media. In a short time,
 numerous small dark globose setose microsclerotia emerged in the colony
 starting from its centre and distributing proportionally throughout agar
 plates. Two PCR primer sets were used to sequences of the ribosomal internal
 transcribed spacer (ITS1 and ITS2) regions. Single products of ~450 bp and
 ~350 bp were amplified by the genus-specific (Cc1F1/Cc2R1) and the
 species-specific primers (Cc1NF1/Cc2NR1), respectively. Morphological,
 cultural and molecular characterization of the isolates from roots and fruits
 showed that root rot and fruit anthracnose of pepper were caused by one and
 the same causal agent determined as C. coccodes. The isolates from roots
 showed rapid mycelial growth, gave rise to numerous minute microsclerotia and
 produced conidia only on SSPA. SSPA supported significantly more mycelium
 growth and sporulation than all other media tested and could be recommended
 for production of large quantity of conidia. No pattern of genetic variation
 associated with the organ or geographic origin of the isolates was
 determined.

http://www.doiserbia.nb.rs/ft.aspx?id=0352-49061324249S

Vasilissa Manova

Papers

DNA damage and repair in plants - from models to crops.

Efficient repair of bleomycin-induced double-strand breaks in barley ribosomal genes.

Karyotype reconstruction modulates the sensitivity of barley genome to radiation-induced DNA and chromosomal damage

Induction and recovery of double-strand breaks in barley ribosomal DNA

Morphological and molecular characterization of Colletotrichum coccodes isolated from pepper cultivated in Bulgaria and Macedonia