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Low-level Gamma Ray Exposure to Rice Seedlings in Iitate Village (Fukushima) Activates Self-defense Responses Unraveled by DNA Microarray Analysis

ABSTRACT: In the summer of 2012, one year after the 3.11 accident at Fukushima Daiichi nuclear power plant following the Great Tohoku Earthquake, a project was initiated to examine the effects of low-level gamma radiation on rice plants. The site of the experiment was the highly contaminated Iitate village in Fukushima prefecture of Japan. The basic experimental strategy was to expose healthy rice seedlings to continuous low-dose gamma radiation and examine the morphological and molecular genetic changes therien. Selected gene expression profiles of internal control, DNA replication/repair, oxidative stress, photosynthesis, and defense/stress functions were examined by semi-quantitative RT-PCR. Results revealed that low-level gamma radiation affects the expression of numerous genes, in particular showing the early (6 h) induction in DNA repair/damage-related genes and the late (72 h) induction of a previously described marker gene for defense/stress responses. Based on these results, which confirmed our data from preliminary experiments using detached rice leaves for radiation exposure, we proceeded for DNA microarray analysis. Using the established dye-swap approach, we analyzed the differentially expressed genes at 6 and 72 h time points using a whole rice genome 4 x 44 K custom chip. Obtained results showed that exposure to low-level gamma radiation differentially regulated 4481 (induced) and 3740 (suppressed) and 2291 (induced) and 1474 (suppressed) rice leaf genes at 6 and 72 h post-exposure, respectively, by at least two-fold changes. MapMan bioinformatics tool was also used to produce diagrams of the potential pathways, based on the input gene expression data of highly changed genes, operating downstream of the gamma radiation perception by rice plant.Inventory of a large number of gamma radiation-responsive genes in leaves provide new information and increased knowledge on novel regulatory processes in rice. The highly contaminated Iitate Farm (ITF), which is located 31 Km from the damaged nuclear power plant and having a background radiation level over 100 times (~ 5 microSv/h) than normal, was the designated place for the re-examination of low-level gamma radiation experiments using rice as a model system. As our group had a decade of experience and data on the effects of gamma radiation on leaf segments, the experimental was designed in such a way so as to expose whole rice plants to gamma radiation being emitted from the contaminated ground and examine the morphological and molecular genetic changes in the leaves under a dose-dependent manner.

ORGANISM(S): Oryza sativa

SUBMITTER: Randeep Rakwal

PROVIDER: E-GEOD-53055 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:In the current study a systematic investigation of life stage, tissue and cell dependent sensitivity to ionizing radiation in the nematode Caenorhabditis elegans was conducted. This revealed that individuals that have reached the post-mitotic L4 stage showed no significant effects with respect to mortality, morbidity or reproduction when subjected to either acute dose ≤6 Gy(1500 mGy/h) or chronic exposure ≤4 Gy( ≤ 100 mGy/h). In contrast, chronic exposure from embryo to young adult stage caused a dose and dose rate dependent reprotoxicitiy with 43% reduction in total brood size at 6.7Gy (107 mGy/h). Systematic targeted irradiation of developmental stages showed that exposure during L1 to young L4 was sufficient to induce reprotoxic effects. Exposure during these stages was associated with a dose rate dependent genotoxic effects on gonads with 1.7 to 3.2 fold increase in germ cell apoptosis in larvae subjected to 40-100 mGy/h, respectively. Importantly, exposure to gamma radiation significantly impaired spermatogenesis in a dose rate dependent manner. The observed reduction in the number of spermatids accounted for xx% of the reprotoxic effects, thus signifying spermatids as the most radiosensitive cell type in C. elegans. Molecular responses analyzed by RNAseq of nematodes irradiated from L1 to L4 stage revealed a significant enrichment of genes related to both male and hermaphrodite reproductive processes. Gene network analysis identified adverse genotoxic effects related to down-regulation of genes required for spindle formation and sperm meiosis/maturation, including smz-1, smz-2 and htas-1. The expression of a subset of 28 set-17 regulated Major Sperm Proteins (MSP) required for spermatids production was correlated to the reduction in reproduction and the number of spermatids, thus corroborating the impairment of spermatogenesis as the major cause of gamma radiation induced life-stage dependent reprotoxic effect. Furthermore, the progeny of irradiated nematodes showed significant embryonal DNA damage that was associated with persistent effect on somatic growth. Unexpectedly, these nematodes did however maintain much of their reproductive capacity in spite of the reduced growth.

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Low-level Gamma Ray Exposure to Rice Seedlings in Iitate Village (Fukushima) Activates Self-defense Responses Unraveled by DNA Microarray Analysis

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