Exposure to Low UV-B Dose Induces DNA Double-Strand Breaks Mediated Onset of Endoreduplication in Vigna radiata (L.) R. Wilczek Seedlings.

Multiple lines of evidence indicate that solar UV-B light acts as an important environmental signal in plants, regulating various cellular and metabolic activities, gene expression, growth and development. Here, we show that low levels of UV-B (4.0 kJ m-2) significantly influence plant response during early seedling development in the tropical legume crop Vigna radiata (L.) R. Wilczek. Exposure to low doses of UV-B showed relatively less growth inhibition yet remarkably enhanced lateral root formation in seedlings. Both low and high (8.0 kJ m-2) doses of UV-B treatment induced DNA double-strand breaks and activated the SOG1-related ATM-ATR-mediated DNA damage response pathway. These effects led to G2-M-phase arrest with a compromised expression of the key cell cycle regulators, including CDKB1;1, CDKB2;1 and CYCB1;1, respectively. However, along with these effects, imbibitional exposure of seeds to a low UV-B dose resulted in enhanced accumulation of FZR1/CCS52A, E2Fa and WEE1 kinase and prominent induction of endoreduplication in 7-day-old seedlings. Low dose of UV-B mediated phenotypical responses, while the onset of endoreduplication appeared to be regulated at least in part via UV-B induced reactive oxygen species accumulation. Transcriptome analyses further revealed a network of co-regulated genes associated with DNA repair, cell cycle regulation and oxidative stress response pathways that are activated upon exposure to low doses of UV-B.

An Insight Into the Mechanism of Plant Organelle Genome Maintenance and Implications of Organelle Genome in Crop Improvement: An Update.

Besides the nuclear genome, plants possess two small extra chromosomal genomes in mitochondria and chloroplast, respectively, which contribute a small fraction of the organelles' proteome. Both mitochondrial and chloroplast DNA have originated endosymbiotically and most of their prokaryotic genes were either lost or transferred to the nuclear genome through endosymbiotic gene transfer during the course of evolution. Due to their immobile nature, plant nuclear and organellar genomes face continuous threat from diverse exogenous agents as well as some reactive by-products or intermediates released from various endogenous metabolic pathways. These factors eventually affect the overall plant growth and development and finally productivity. The detailed mechanism of DNA damage response and repair following accumulation of various forms of DNA lesions, including single and double-strand breaks (SSBs and DSBs) have been well documented for the nuclear genome and now it has been extended to the organelles also. Recently, it has been shown that both mitochondria and chloroplast possess a counterpart of most of the nuclear DNA damage repair pathways and share remarkable similarities with different damage repair proteins present in the nucleus. Among various repair pathways, homologous recombination (HR) is crucial for the repair as well as the evolution of organellar genomes. Along with the repair pathways, various other factors, such as the MSH1 and WHIRLY family proteins, WHY1, WHY2, and WHY3 are also known to be involved in maintaining low mutation rates and structural integrity of mitochondrial and chloroplast genome. SOG1, the central regulator in DNA damage response in plants, has also been found to mediate endoreduplication and cell-cycle progression through chloroplast to nucleus retrograde signaling in response to chloroplast genome instability. Various proteins associated with the maintenance of genome stability are targeted to both nuclear and organellar compartments, establishing communication between organelles as well as organelles and nucleus. Therefore, understanding the mechanism of DNA damage repair and inter compartmental crosstalk mechanism in various sub-cellular organelles following induction of DNA damage and identification of key components of such signaling cascades may eventually be translated into strategies for crop improvement under abiotic and genotoxic stress conditions. This review mainly highlights the current understanding as well as the importance of different aspects of organelle genome maintenance mechanisms in higher plants.

Assessment of cytotoxic and genotoxic potentials of a mononuclear Fe(II) Schiff base complex with photocatalytic activity in Trigonella.

BACKGROUND: In recent times, coordination complexes of iron in various oxidation states along with variety of ligand systems have been designed and developed for effective treatment of cancer cells without adversely affecting the normal cell and tissues of various organs. METHODS: In this study, we have evaluated the mechanism of action of a Fe(II) Schiff base complex in the crop plant Trigonella foenum-graecum L. (Fenugreek) as the screening system by using morphological, cytological, biochemical and molecular approaches. Further functional characterization was performed using MCF-7 cell line and solid tumour model for the assessment of anti-tumour activity of the complex. RESULTS: Our results indicate efficiency of the Fe(II) Schiff base complex in the induction of double strand breaks in DNA. Complex treatment clearly induced cytotoxic and genotoxic damage in Trigonella seedlings. The Fe-complex treatment caused cell cycle arrest via the activation of ATM-ATR kinase mediated DNA damage response pathway with the compromised expression of CDK1, CDK2 and CyclinB1 protein in Trigonella seedlings. In cultured MCF-7 cells, the complex induces cytotoxicity and DNA fragmentation through intracellular ROS generation. Fe-complex treatment inhibited tumour growth in solid tumour model with no additional side effects. CONCLUSION: The growth inhibitory and cytotoxic effects of the complex result from activation of DNA damage response along with oxidative stress and cell cycle arrest. GENERAL SIGNIFICANCE: Overall, our results have provided comprehensive information on the mechanism of action and efficacy of a Fe(II) Schiff base complex in higher eukaryotic genomes and indicated its future implications as potential therapeutic agent.

Pesticide mediated oxidative stress induces genotoxicity and disrupts chromatin structure in fenugreek (Trigonella foenum - graecum L.) seedlings.

Here we report cytototoxic and genotoxic potentials of four commonly used pesticides, including, tricyclazole, thiabendazole (fungicides), plethora and slash-360 (insecticides) in the non-target tropical crop plant Trigonella foenum - graecum L. (fenugreek). Three different concentrations of the selected pesticides were used. For fungicides, 0.05% and for insecticides, 0.1% concentration represents recommended doses, while, 2X and 4X concentrations of the recommended dose were used to test their phytotoxic effects. Inhibition of germination and seedling growth were clearly observed at 4X concentration of the pesticides. Tricyclazole and plethora showed more pronounced effects than the other two agrochemicals. The pesticides, particularly at 4X concentrations clearly induced oxidative stress and cytotoxic effects in Trigonella seedlings with appreciable reduction in mitotic index, induction of chromosomal abnormalities in root meristematic cell and decreased level of accumulation of some key cell cycle regulators, including CDK1, CDK2 and Cyclin B1.Detection of accumulation of DNA double strand breaks and histone H2AX phosphorylation in pesticide treated seedlings have revealed direct genotoxic effects of the selected pesticides. Overall, our results provide insights into the mechanism of pesticide induced cytotoxic and genotoxic effects in plant genome with future implications for designing pesticides to minimize their deleterious effects on non-target crop plants.

Oxidative and genotoxic damages in plants in response to heavy metal stress and maintenance of genome stability.

Plants, being sessile in nature, are constantly exposed to various environmental stresses, such as solar UV radiations, soil salinity, drought and desiccation, rehydration, low and high temperatures and other vast array of air and soil borne chemicals, industrial waste products, metals and metalloids. These agents, either directly or indirectly via the induction of oxidative stress and overproduction of reactive oxygen species (ROS), frequently perturb the chemical or physical structures of DNA and induce both cytotoxic or genotoxic stresses. Such condition, in turn, leads to genome instability and thus eventually severely affecting plant health and crop yield. With the growing industrialization process and non-judicious use of chemical fertilizers, the heavy metal mediated chemical toxicity has become one of the major environmental threats for the plants around the globe. The heavy metal ions cause damage to the structural, enzymatic and non-enzymatic components of plant cell, often resulting in loss of cell viability, thus negatively impacting plant growth and development. Plants have also evolved with an extensive and highly efficient mechanism to respond and adapt under such heavy metal toxicity mediated stress conditions. In addition to morpho-anatomical, hormonal and biochemical responses, at the molecular level, plants respond to heavy metal stress induced oxidative and genotoxic damage via the rapid change in the expression of the responsive genes at the transcriptional level. Various families of transcription factors play crucial role in triggering such responses. Apart from transcriptional response, epigenetic modifications have also been found to be essential for maintenance of plant genome stability under genotoxic stress. This review represents a comprehensive survey of recent advances in our understanding of plant responses to heavy metal mediated toxicity in general with particular emphasis on the transcriptional and epigenetic responses and highlights the importance of understanding the potential targets in the associated pathways for improved stress tolerance in crops.