Abscopal mutagenic effect of low-energy-ions inArabidopsis Thalianaseeds

Stress Management in Plants: Examining Provisional and Unique Dose-Dependent Responses

The purpose of this review is to critically evaluate the effects of different stress factors on higher plants, with particular attention given to the typical and unique dose-dependent responses that are essential for plant growth and development. Specifically, this review highlights the impact of stress on genome instability, including DNA damage and the molecular, physiological, and biochemical mechanisms that generate these effects. We provide an overview of the current understanding of predictable and unique dose-dependent trends in plant survival when exposed to low or high doses of stress. Understanding both the negative and positive impacts of stress responses, including genome instability, can provide insights into how plants react to different levels of stress, yielding more accurate predictions of their behavior in the natural environment. Applying the acquired knowledge can lead to improved crop productivity and potential development of more resilient plant varieties, ensuring a sustainable food source for the rapidly growing global population.

Isolation, Mutagenesis, and Organic Acid Secretion of a Highly Efficient Phosphate-Solubilizing Fungus

The highly effective phosphate-solubilizing microorganisms are significant for making full use of the potential phosphorus resources in the soil and alleviating the shortage of phosphorus resources. In this study, a phosphate-solubilizing fungus was isolated from wheat and cotton rhizosphere soils in the lower reaches of the Yellow River in China and was identified as Penicillium oxalicum by morphological and ITS sequencing analysis. In order to obtain a fungus with more efficient phosphorus solubilization ability, we tested three positive mutant strains (P1, P2, and P3) and three negative mutant strains (N1, N2, and N3) through low-energy nitrogen ion implantation mutagenesis. Compared with the parental strain, the phosphate-solubilizing capacity of P1, P2, and P3 was enhanced by 56.88%, 42.26%, and 32.15%, respectively, and that of N1, N2, and N3 was weakened by 47.53%, 35.27%, and 30.86%, respectively. Compared with the parental strain, the total amount of organic acids secreted significantly increased in the three positive mutant strains and decreased in the negative mutant strains; the pH of culture medium was significantly lower in the positive mutant strains and higher in the negative mutant strains. The capacity of phosphate-solubilizing fungus to secrete organic acids and reduce the growth-medium pH was closely related to its phosphate-solubilizing ability. The changes in the amount of organic acids secreted by mutants can alter their acidification and phosphate-solubilizing capacity. In conclusion, this study offers a theoretical basis and strain materials for the exploration and application of phosphate-solubilizing fungi.

From Classical Radiation to Modern Radiation: Past, Present, and Future of Radiation Mutation Breeding

Radiation mutation breeding has been used for nearly 100 years and has successfully improved crops by increasing genetic variation. Global food production is facing a series of challenges, such as rapid population growth, environmental pollution and climate change. How to feed the world's enormous human population poses great challenges to breeders. Although advanced technologies, such as gene editing, have provided effective ways to breed varieties, by editing a single or multiple specific target genes, enhancing germplasm diversity through mutation is still indispensable in modern and classical radiation breeding because it is more likely to produce random mutations in the whole genome. In this short review, the current status of classical radiation, accelerated particle and space radiation mutation breeding is discussed, and the molecular mechanisms of radiation-induced mutation are demonstrated. This review also looks into the future development of radiation mutation breeding, hoping to deepen our understanding and provide new vitality for the further development of radiation mutation breeding.

Negative Modulation of Bystander DNA Repair Potential by X-Ray Targeted Tissue Volume in Arabidopsis thaliana

Radiation-induced bystander effects (RIBE) entail a cascade of bystander signals produced by the hit cells to the neighboring cells to regulate various biological processes including DNA damage repair. However, there is little clarity regarding the effect of radiation-targeted volume (hit cell amount) on the DNA repair potential of the bystander cells. This is especially important to understand in the context of the whole organism, where the target usually consists of multiple types of cells/tissues. To address this question, model plant Arabidopsis thaliana was locally irradiated, and the DNA repair potential of bystander root-tip cells was assessed based on their radioresistance to subsequent high-dose radiation, i.e. radioadaptive responses (RAR). We found that X-ray irradiation of the aerial parts (AP) of A. thaliana seedlings (5 Gy) initiated RAR in the root-tip cells, which exhibited an alleviated repression of root growth and root cell division, and reduced amount of DNA strand breaks. We also observed an improvement in the repair efficiency of the homologous recombination (HR) and non-homologous end joining (NHEJ) pathways in the bystander root tip cells. We further expanded the X-ray targeted volume to include the aerial parts with upper parts of the primary root and compared it with X-ray irradiated aerial parts alone. Comparative analysis revealed that RAR for these end points either disappeared or decreased; specifically, the repair efficiency of HR was significantly reduced, indicating that radiation-targeted volume negatively modulates the bystander DNA repair potential. In contrast, X-ray irradiation of upper part of the primary root alone did not induce RAR of the root tip cells. Thus, we propose that additional X-ray irradiation of upper part of the primary root reduces the bystander DNA repair potential, possibly by selectively disturbing the transport of bystander signals responsible for HR repair.

Changes in gene expression as one of the key mechanisms involved in radiation-induced bystander effect

The radiation-induced bystander effect (RIBE) refers to the manifestation of responses by non-targeted/non-hit cells or tissues situated in proximity to cells and tissues directly exposed to ionizing radiation (IR). The RIBE is elicited by agents and factors released by IR-hit cells. The growing body of data suggests that the underlying mechanisms of the RIBE are multifaceted depending both on the biological (characteristics of directly IR-exposed cells, bystander cells, intercellular milieu) and the physical (dose, rate and type of IR, time after exposure) factors/parameters. Although the exact identity of bystander signal(s) is yet to be identified, the published data indicate changes in gene expression for multiple types of RNA (mRNA, microRNA, mitochondrial RNA, long non-coding RNA, small nucleolar RNA) as being one of the major responses of cells and tissues in the context of the RIBE. Gene expression profiles demonstrate a high degree of variability between distinct bystander cell and tissue types. These alterations could independently, or in a signaling cascade, result in the manifestation of readily observable endpoints, including changes in viability and genomic instability. Here, the relevant publications on the gene candidates and signaling pathways involved in the RIBE are reviewed, and a framework for future studies, both in vitro and in vivo, on the genetic aspect of the RIBE is provided.

A pivotal role of the jasmonic acid signal pathway in mediating radiation-induced bystander effects in Arabidopsis thaliana

Although radiation-induced bystander effects (RIBE) in Arabidopsis thaliana have been well demonstrated in vivo, little is known about their underlying mechanisms, particularly with regard to the participating signaling molecules and signaling pathways. In higher plants, jasmonic acid (JA) and its bioactive derivatives are well accepted as systemic signal transducers that are produced in response to various environmental stresses. It is therefore speculated that the JA signal pathway might play a potential role in mediating radiation-induced bystander signaling of root-to-shoot. In the present study, pretreatment of seedlings with Salicylhydroxamic acid, an inhibitor of lipoxigenase (LOX) in JA biosynthesis, significantly suppressed RIBE-mediated expression of the AtRAD54 gene. After root irradiation, the aerial parts of A. thaliana mutants deficient in JA biosynthesis (aos) and signaling cascades (jar1-1) showed suppressed induction of the AtRAD54 and AtRAD51 genes and TSI and 180-bp repeats, which have been extensively used as endpoints of bystander genetic and epigenetic effects in plants. These results suggest an involvement of the JA signal pathway in the RIBE of plants. Using the root micro-grafting technique, the JA signal pathway was shown to participate in both the generation of bystander signals in irradiated root cells and radiation responses in the bystander aerial parts of plants. The over-accumulation of endogenous JA in mutant fatty acid oxygenation up-regulated 2 (fou2), in which mutation of the Two Pore Channel 1 (TPC1) gene up-regulates expression of the LOX and allene oxide synthase (AOS) genes, inhibited RIBE-mediated expression of the AtRAD54 gene, but up-regulated expression of the AtKU70 and AtLIG4 genes in the non-homologous end joining (NHEJ) pathway. Considering that NHEJ is employed by plants with increased DNA damage, the switch from HR to NHEJ suggests that over-accumulation of endogenous JA might enhance the radiosensitivity of plants in terms of RIBE.

Effects of low-energy N(+)-beam implantation on root growth in Arabidopsis seedlings

The effects of ion implantation on the morphology changes and biological responses of plants are dependent on implantation doses. Previous studies mainly focus on the application of ion-beam technology in genetic mutation. Our knowledge regarding the mechanism underlying the plant growth inhibition induced by ion implantation remains limited. In this study, we explore the responses of root growth to low-energy N(+)-beam implantation using implanted Arabidopsis seeds. Our results showed that the root and root tip length were obviously reduced by implantation with large doses of low-energy N(+) beam. The analysis of confocal images showed that ion implantation reduced the cell viability and cell division activity in root meristem. The production rate of superoxide radical (O2(•-)) and contents of hydrogen peroxide (H2O2) in roots under ion implantation were markedly higher than those of controls. Transcriptional expression analysis of selected genes revealed that Arabidopsis RBOH genes associated with reactive oxygen species (ROS) production were significantly up-regulated in roots in response to ion implantation. The activities of antioxidant enzymes were also induced by ion implantation. Moreover, ROS scavenging obviously enhanced cell viability and cell division in response to ion implantation and alleviated the root growth inhibition of the implanted seedlings. Our results suggest that the overproduction of ROS induced by ion implantation is involved in the inhibitory effect of low-energy ion beam on root growth by affecting the cell viability and cell division of root meristem in Arabidopsis seedlings.

Modulation of modeled microgravity on radiation-induced bystander effects in Arabidopsis thaliana

Both space radiation and microgravity have been demonstrated to have inevitable impact on living organisms during space flights and should be considered as important factors for estimating the potential health risk for astronauts. Therefore, the question whether radiation effects could be modulated by microgravity is an important aspect in such risk evaluation. Space particles at low dose and fluence rate, directly affect only a fraction of cells in the whole organism, which implement radiation-induced bystander effects (RIBE) in cellular response to space radiation exposure. The fact that all of the RIBE experiments are carried out in a normal gravity condition bring forward the need for evidence regarding the effect of microgravity on RIBE. In the present study, a two-dimensional rotation clinostat was adopted to demonstrate RIBE in microgravity conditions, in which the RIBE was assayed using an experimental system of root-localized irradiation of Arabidopsis thaliana (A. thaliana) plants. The results showed that the modeled microgravity inhibited significantly the RIBE-mediated up-regulation of expression of the AtRAD54 and AtRAD51 genes, generation of reactive oxygen species (ROS) and transcriptional activation of multicopy P35S:GUS, but made no difference to the induction of homologous recombination by RIBE, showing divergent responses of RIBE to the microgravity conditions. The time course of interaction between the modeled microgravity and RIBE was further investigated, and the results showed that the microgravity mainly modulated the processes of the generation or translocation of the bystander signal(s) in roots.

Embryos of the zebrafish Danio rerio in studies of non-targeted effects of ionizing radiation

The use of embryos of the zebrafish Danio rerio as an in vivo tumor model for studying non-targeted effects of ionizing radiation was reviewed. The zebrafish embryo is an animal model, which enables convenient studies on non-targeted effects of both high-linear-energy-transfer (LET) and low-LET radiation by making use of both broad-beam and microbeam radiation. Zebrafish is also a convenient embryo model for studying radiobiological effects of ionizing radiation on tumors. The embryonic origin of tumors has been gaining ground in the past decades, and efforts to fight cancer from the perspective of developmental biology are underway. Evidence for the involvement of radiation-induced genomic instability (RIGI) and the radiation-induced bystander effect (RIBE) in zebrafish embryos were subsequently given. The results of RIGI were obtained for the irradiation of all two-cell stage cells, as well as 1.5 hpf zebrafish embryos by microbeam protons and broad-beam alpha particles, respectively. In contrast, the RIBE was observed through the radioadaptive response (RAR), which was developed against a subsequent challenging dose that was applied at 10 hpf when <0.2% and <0.3% of the cells of 5 hpf zebrafish embryos were exposed to a priming dose, which was provided by microbeam protons and broad-beam alpha particles, respectively. Finally, a perspective on the field, the need for future studies and the significance of such studies were discussed.

Novel features of radiation-induced bystander signaling in Arabidopsis thaliana demonstrated using root micro-grafting

Radiation-induced bystander effects (RIBE) have been well demonstrated in whole organisms, as well as in single-cell culture models in vitro and multi-cellular tissues models in vitro, however, the underlying mechanisms remain unclear, including the temporal and spatial course of bystander signaling. The RIBE in vivo has been shown to exist in the model plant Arabidopsis thaliana (A. thaliana). Importantly, the unique plant grafting provides a delicate approach for studying the temporal and spatial course of bystander signaling in the context of whole plants. In our previous study, the time course of bystander signaling in plants has been well demonstrated using the root micro-grafting technique. In this study, we further investigated the temporal cooperation pattern of multiple bystander signals, the directionality of bystander signaling, and the effect of bystander tissues on the bystander signaling. The results showed that the bystander response could also be induced efficiently when the asynchronously generated bystander signals reached the bystander tissues in the same period, but not when they entered into the bystander tissues in an inversed sequence. The absence of bystander response in root-inversed grafting indicated that the bystander signaling along roots might be of directionality. The bystander signaling was shown to be independent of the bystander tissues.

Homologous recombination in Arabidopsis seeds along the track of energetic carbon ions

Heavy ion irradiation has been used as radiotherapy of deep-seated tumors, and is also an inevitable health concern for astronauts in space mission. Unlike photons such as X-rays and γ-rays, a high linear energy transfer (LET) heavy ion has a varying energy distribution along its track. Therefore, it is important to determine the correlation of biological effects with the Bragg curve energy distribution of heavy ions. In this study, a continuous biological tissue equivalent was constructed using a layered cylinder of Arabidopsis seeds, which was irradiated with carbon ions of 87.5MeV/nucleon. The position of energy loss peak in the seed pool was determined with CR-39 track detectors. The mutagenic effect in vivo along the path of carbon ions was investigated with the seeds in each layer as an assay unit, which corresponded to a given position in physical Bragg curve. Homologous recombination frequency (HRF), expression level of AtRAD54 gene, germination rate of seeds, and survival rate of young seedlings were used as checking endpoints, respectively. Our results showed that Arabidopsis S0 and S1 plants exhibited significant increases in HRF compared to their controls, and the expression level of AtRAD54 gene in S0 plants was significantly up-regulated. The depth-biological effect curves for HRF and the expression of AtRAD54 gene were not consistent with the physical Bragg curve. Differently, the depth-biological effect curves for the developmental endpoints matched generally with the physical Bragg curve. The results suggested a different response pattern of various types of biological events to heavy ion irradiation. It is also interesting that except for HRF in S0 plants, the depth-biological effect curves for each biological endpoint were similar for 5Gy and 30Gy of carbon irradiation.