Rapid identification of mutations caused by fast neutron bombardment in Medicago truncatula

Background Fast neutron bombardment (FNB) is a very effective approach for mutagenesis and has been widely used in generating mutant libraries in many plant species. The main type of mutations of FNB mutants are deletions of DNA fragments ranging from few base pairs to several hundred kilobases, thus usually leading to the null mutation of genes. Despite its efficiency in mutagenesis, identification of the mutation sites is still challenging in many species. The traditional strategy of positional cloning is very effective in identifying the mutation but time-consuming. With the availability of genome sequences, the array-based comparative genomic hybridization (CGH) method has been developed to detect the mutation sites by comparing the signal intensities of probes between wild-type and mutant plants. Though CGH method is effective in detecting copy number variations (CNVs), the resolution and coverage of CGH probes are not adequate to identify mutations other than CNVs. Results We report a new strategy and pipeline to sensitively identify the mutation sites of FNB mutants by combining deep-coverage whole-genome sequencing (WGS), polymorphism calling, and customized filtering in Medicago truncatula. Initially, we performed a bulked sequencing for a FNB white nodule (wn) mutant and its wild-type like plants derived from a backcross population. Following polymorphism calling and filtering, validation by manual check and Sanger sequencing, we identified that SymCRK is the causative gene of white nodule mutant. We also sequenced an individual FNB mutant yellow leaves 1 (yl1) and wild-type plant. We identified that ETHYLENE-DEPENDENT GRAVITROPISM-DEFICIENT AND YELLOW-GREEN 1 (EGY1) is the candidate gene for M. truncatula yl1 mutant. Conclusion Our results demonstrated that the method reported here is rather robust in identifying the mutation sites for FNB mutants.

Nanostructure Self-Organization as Cause of Wavelike Radiation Embrittlement of the RPV Steel

Influence of neutron irradiation on reactor pressure vessel (RPV) steel degradation are examined with reference to the possible reasons of the substantial experimental data scatter and furthermore-nonstandard (non-monotonous) and oscillatory embrittlement behavior. In our glance this phenomenon may be explained by presence of the wavelike recovering component in the embrittlement kinetics. In our opinion controversy in the estimation on neutron flux on radiation degradation impact may be explained by presence of the wavelike component in the embrittlement kinetics. Therefore flux effect manifestation depends on fluence level. At low fluencies radiation degradation has to exceed normative value, then approaches to normative meaning and finally became sub normative. As a result of dose rate effect manifestation peripheral RPV’s zones in some range of fluencies have to be damaged to a large extent than situated closely to core. Moreover as a hypothesis we suppose that at some stages of irradiation damaged metal have to be partially restored by irradiation i.e. neutron bombardment. Nascent during irradiation nanostructure undergo occurring once or periodically evolution in a direction both degradation and recovery of the initial properties. According to our hypothesis at some stage(s) of metal nanostructure degradation neutron bombardment became recovering factor. As a result oscillation arise that in tern lead to enhanced data scatter. In this case we have to consider irradiation as a recovery factor. Disclosure of the steel degradation oscillating is a sign of the steel nanostructure cyclic self-recovery transformation as it take place in self-organization processes.