Sungbeom Lee

Ameliorative effects of squash (Cucurbita moschata Duchesne ex Poiret) leaf extracts on oxidative stress

This study screened paraquat-tolerant plants among 10 plant species, including monocots and dicots angiosperms. Squash (Cucurbita moschata Duchesne ex Poiret) and kidney bean (Phaseolus vulgaris L.) plants exhibited the highest photooxidation-tolerant phenotypes upon a foliar treatment with paraquat. A foliar treatment with paraquat pre-mixed with leaf water extracts from the squash plant significantly alleviated paraquat-induced oxidative damage in maize, but this was not the case after a treatment with the hydrophobic phase of the leaf extracts. In particular, the water extract from young leaves (4th true leaf) of squash plants conferred tenfold higher tolerance to oxidative damage in paraquat-treated leave tissues compared to paraquat-only treatment. This tolerance was tightly linked not only to the increased amounts of ascorbic acid and dehydroascorbate antioxidants in the damaged leaves, but also to the reduced chlorophyll loss, lipid peroxidation, and cellular electrolyte leakage. Moreover, the protective effects of the water extract were apparent when using another bipyridyl herbicide, diquat, but not with a diphenyl-ether herbicide, oxyfluorfen. On the other hand, pre-treatment with the extract prior to the onset of drought or cold stress had no significant antioxidative effect on the treated tissues.

Arabidopsis Basic Helix-Loop-Helix 34 (bHLH34) Is Involved in Glucose Signaling through Binding to a GAGA Cis-Element

The modulation of glucose (Glc) homeostasis and signaling is crucial for plant growth and development. Nevertheless, the molecular signaling mechanism by which a plant senses a cellular Glc level and coordinates the expression of Glc-responsive genes is still incompletely understood. Previous studies have shown that Arabidopsis thaliana plasma membrane Glc-responsive regulator (AtPGR) is a component of the Glc-responsive pathway. Here, we demonstrated that a transcription factor bHLH34 binds to 5′-GAGA-3′ element of the promoter region of AtPGR in vitro, and activates beta-glucuronidase (GUS) activity upon Glc treatment in AtPGR promoter-GUS transgenic plants. Gain- and loss-of-function analyses suggested that the bHLH34 involved in the responses to not only Glc, but also abscisic acid (ABA) and salinity. These results suggest that bHLH34 functions as a transcription factor in the Glc-mediated stress responsive pathway as well as an activator of AtPGR transcription. Furthermore, genetic experiments revealed that in Glc response, the functions of bHLH34 are different from that of a bHLH104, a homolog of bHLH34. Collectively, our findings indicate that bHLH34 is a positive regulator of Glc, and may affect ABA or salinity response, whereas bHLH104 is a negative regulator and epistatic to bHLH34 in the Glc response.

Ionizing radiation manifesting DNA damage response in plants: An overview of DNA damage signaling and repair mechanisms in plants

Plants orchestrate various DNA damage responses (DDRs) to overcome the deleterious impacts of genotoxic agents on genetic materials. Ionizing radiation (IR) is widely used as a potent genotoxic agent in plant DDR research as well as plant breeding and quarantine services for commercial uses. This review aimed to highlight the recent advances in cellular and phenotypic DDRs, especially those induced by IR. Various physicochemical genotoxic agents damage DNA directly or indirectly by inhibiting DNA replication. Among them, IR-induced DDRs are considerably more complicated. Many aspects of such DDRs and their initial transcriptomes are closely related to oxidative stress response. Although many key components of DDR signaling have been characterized in plants, DDRs in plant cells are not understood in detail to allow comparison with those in yeast and mammalian cells. Recent studies have revealed plant DDR signaling pathways including the key regulator SOG1. The SOG1 and its upstream key components ATM and ATR could be functionally characterized by analyzing their knockout DDR phenotypes after exposure to IR. Considering the potent genotoxicity of IR and its various DDR phenotypes, IR-induced DDR studies should help to establish an integrated model for plant DDR signaling pathways by revealing the unknown key components of various DDRs in plants.

A Pyridazine-Based Fluorescent Probe Targeting Aβ Plaques in Alzheimer’s Disease

Accumulation of β-amyloid (Aβ) plaques comprising Aβ40 and Aβ42 in the brain is the most significant factor in the pathogenesis of Alzheimers disease (AD). Thus, the detection of Aβ plaques has increasingly attracted interest in the context of AD diagnosis. In the present study, a fluorescent pyridazine-based dye that can detect and image Aβ plaques was designed and synthesized, and its optical properties in the presence of Aβ aggregates were evaluated. An approximately 34-fold increase in emission intensity was exhibited by the fluorescent probe after binding with Aβ aggregates, for which it showed high affinity (KD = 0.35 µM). Moreover, the reasonable hydrophobic properties of the probe (log P = 2.94) allow it to penetrate the blood brain barrier (BBB). In addition, the pyridazine-based probe was used in the histological costaining of transgenic mouse (APP/PS1) brain sections to validate the selective binding of the probe to Aβ plaques. The results suggest that the pyridazine-based compound has the potential to serve as a fluorescent probe for the diagnosis of AD.

Reduced Expression of Gongdae Ring Zinc Finger 1 (GdRZF1) Enhances Drought Stress Tolerance in Watermelon (Citrullus lanatus)

Watermelon is a major fruit vegetable around the world. Drought is an abiotic stress factor that affects the productivity and growth of crop plants. To improve the tolerance of watermelon to drought stress, it is important to isolate stress tolerance-related genes. Recently, we characterized the gene for a ubiquitin E3 ligase protein named Lagenaria siceraria RING Zinc Finger 1 (LsRZF1) . In Arabidopsis , LsRZF1 is involved in the drought response through the proline metabolism-mediated pathway. In this study, we identified and characterized a watermelon (Citrullus lanatus cv. Gongdae) homolog of LsRZF1, designated GdRZF1. LsRZF1 antisense (lsrzf1) transgenic watermelon lines showed reduced GdRZF1 expression, and were less sensitive to drought stress than the wild type. Reduced expression of GdRZF1 was also significantly influential in changes in drought-sensitive parameters including relative water content, ion leakage, chlorophyll content, malondialdehyde levels, proline content, and the expression of drought stress-associated genes. Taken together, these findings suggest that GdRZF1 is important for water deficit tolerance in watermelon. OPEN ACCESS Received:

Loss of Ribosomal Protein L24A (RPL24A) suppresses proline accumulation of Arabidopsis thaliana ring zinc finger 1 (atrzf1) mutant in response to osmotic stress

Proline (Pro) metabolism in plants is involved in various cellular processes mediated during abiotic stress. However, the Pro-regulatory mechanisms are unclear. We used a suppressor mutation technique to isolate novel genes involved in the regulation of Pro metabolism in Arabidopsis. Using atrzf1 as a parental plant for T-DNA tagging mutagenesis, we identified a suppressor mutant, termed proline content alterative 21 (pca21), that displayed reduced Pro contents compared with the atrzf1 under osmotic stress conditions. Genomic Thermal Asymmetric Interlaced (TAIL)-PCR revealed pca21 harbored an inserted T-DNA in the region of At2g36620 that encodes Ribosomal Protein L24A. In general, the pca21 mutant partially suppressed the insensitivity of atrzf1 to osmotic stress and abscisic acid during seed germination and early seedling stage. Additionally, the pca21 mutant had increased MDA content and lower expression of several Pro biosynthesis-related genes than the atrzf1 mutant during drought condition. These results suggest that pca21 acts as partial suppressor of atrzf1 in the osmotic stress response through the Pro-mediated pathway.