Bohan Liu

Toxicological effects of bisphenol A on growth and antioxidant defense system in Oryza sativa as revealed by ultrastructure analysis.

The present study was conducted to evaluate the effect of bisphenol A (BPA) on rice seedlings grown in a hydroponic system. The obtained results demonstrated that at lower concentration (up to 10µM) BPA had some stimulatory effects on the growth of rice seedlings but at higher doses it significantly inhibited seedlings growth. The photosynthetic pigments were significantly decreased by high doses of BPA. Exposure to BPA caused increased membrane permeability in root cells and resulted in increased concentration of reactive oxygen species (ROS) and increased lipid peroxidation as revealed by thiobarbituric acid reactive substances (TBARS) assay. In leaves, superoxide dismutase (SOD) activity exhibited an increase at lower concentrations of BPA but was inhibited at the highest dose (200µM) of BPA. At 100µM of BPA, a significant increase in antioxidant activities in leaves was observed but at 200µM this activity was inhibited. In roots, a significant decrease in enzymes activity was recorded at the highest concentration of BPA (200µM); however, ascorbate peroxidase (APX) and catalase (CAT) activities were significantly increased at the concentrations of 10 and 50µM in comparison to the control. Moreover, the present results revealed that BPA severely affected cell organelles in rice seedlings. It can be concluded that the observed adverse effects in rice seedlings by BPA in the present study could be attributed to the oxidative stress caused by BPA.

ABA-induced CCCH tandem zinc finger protein OsC3H47 decreases ABA sensitivity and promotes drought tolerance in Oryza sativa.

Water deficit causes multiple negative impacts on plants, such as reactive oxygen species (ROS) accumulation, abscisic acid (ABA) induction, stomatal closure, and decreased photosynthesis. Here, we characterized OsC3H47, which belongs to CCCH zinc-finger families, as a drought-stress response gene. It can be strongly induced by NaCl, PEG, ABA, and drought conditions. Overexpression of OsC3H47 significantly enhanced tolerance to drought and salt stresses in rice seedlings, which indicates that OsC3H47 plays important roles in post-stress recovery. However, overexpression of OsC3H47 reduced the ABA sensitivity of rice seedlings. This suggests that OsC3H47 is a newly discovered gene that can control rice drought-stress response, and it may play an important role in ABA feedback and post-transcription processes.

AtGIS, a C2H2 zinc-finger transcription factor from Arabidopsis regulates glandular trichome development through GA signaling in tobacco

Glandular trichome is specialized multicellular structures that have capability to synthesize and secrete secondary metabolites and protect plants from biotic and abiotic stresses. Our previous results revealed that the C2H2 zinc-finger transcription factors (GIS) acts upstream of GL3/EGL3-GL1-TTG1transcriptional activator complex to regulate trichome initiation through GA signal in Arabidopsis. In the present study, we are reporting that ectopic expression of AtGIS could regulate glandular trichome development through GA signaling in tobacco. X-gluc staining of various organs from transgenic plants showed that AtGIS expressed mainly in the glandular trichomes. Statistical analysis demonstrated that over expression of GIS increased significantly glandular trichome production on the leaf, stem, branch, and sepal in tobacco. After PAC treatment, reduction of glandular trichome production in transgenic plants was more severe with compared to wild type plants. Furthermore, GA treatment could induce expression of AtGIS. More importantly, our results also demonstrated that overexpressed AtGIS significantly affect the main components of trichome exudates, such as significantly increase the content of nicotine, Cembratriene-4, 6-diol. Taken together, these results suggest that ectopic expression of AtGIS regulates glandular trichome development and may play a key role in compounds secretion in tobacco.

Involvement of C2H2 zinc finger proteins in the regulation of epidermal cell fate determination in Arabidopsis

Cell fate determination is a basic developmental process during the growth of multicellular organisms. Trichomes and root hairs of Arabidopsis are both readily accessible structures originating from the epidermal cells of the aerial tissues and roots respectively, and they serve as excellent models for understanding the molecular mechanisms controlling cell fate determination and cell morphogenesis. The regulation of trichome and root hair formation is a complex program that consists of the integration of hormonal signals with a large number of transcriptional factors, including MYB and bHLH transcriptional factors. Studies during recent years have uncovered an important role of C2H2 type zinc finger proteins in the regulation of epidermal cell fate determination. Here in this minireview we briefly summarize the involvement of C2H2 zinc finger proteins in the control of trichome and root hair formation in Arabidopsis.

The Arabidopsis Gene zinc finger protein 3(ZFP3) Is Involved in Salt Stress and Osmotic Stress Response

Plants are continuously challenged by various abiotic and biotic stresses. To tide over these adversities, plants evolved intricate regulatory networks to adapt these unfavorable environments. So far, many researchers have clarified the molecular and genetic pathways involved in regulation of stress responses. However, the mechanism through which these regulatory networks operate is largely unknown. In this study, we cloned a C2H2-type zinc finger protein gene ZFP3 from Arabidopsis thaliana and investigated its function in salt and osmotic stress response. Our results showed that the expression level of ZFP3 was highly suppressed by NaCl, mannitol and sucrose. Constitutive expression of ZFP3 enhanced tolerance of plants to salt and osmotic stress while the zfp3 mutant plants displays reduced tolerance in Arabidopsis. Gain- and Loss-of-function studies of ZFP3 showed that ZFP3 significantly changes proline accumulation and chlorophyll content. Furthermore, over-expression of ZFP3 induced the expressions of stress-related gene KIN1, RD22, RD29B and AtP5CS1. These results suggest that ZFP3 is involved in salt and osmotic stress response.

Biochemical responses and ultrastructural changes in ethylene insensitive mutants of Arabidopsis thialiana subjected to bisphenol A exposure

Bisphenol A (BPA), an important raw material in plastic industry, has become a serious environmental contaminant due to its wide spread use in different products and increasing release into the environment. BPA is known to cause adverse effects in living organisms including plants. Several studies reported that BPA affects growth and development in plants, mainly through oxidative stress. Plants are known to generally cope with stress mainly through hormonal regulation and adaptation, but little is known about the role of plant hormones in plants under BPA stress. The present study was conducted to investigate the role of ethylene in BPA induced oxidative stress in plants using Arabidopsis thaliana as a test plant. The response of ethylene insensitive mutants of Arabidopsis (ein2-1 and etr1-3) to BPA exposure was studied in comparison to the wild type Arabidopsis (WT). In all three genotypes, exposure to BPA adversely affected cellular structures, stomata and light-harvesting pigments. An increase in reactive oxygen species (ROS) lipid peroxidation and other oxidative stress markers indicated that BPA induced toxicity through oxidative stress. However, the overall results revealed that WT Arabidopsis had more pronounced BPA induced damages while ein2-1 and etr1-3 mutants withstood the BPA induced stress more efficiently. The activity of antioxidant enzymes and expression of antioxidants related genes revealed that the antioxidant defense system in both mutants was more efficiently activated than in WT against BPA induced oxidative stress, which further evidenced the involvement of ethylene in regulating BPA induced oxidative stress. It is concluded that ethylene perception and signaling may be involved in BPA induced oxidative stress responses in plants.

Ethylene mediates dichromate-induced inhibition of primary root growth by altering AUX1 expression and auxin accumulation in Arabidopsis thaliana : Cr(VI) inhibits primary root via ethylene & auxin

The hexavalent form of chromium [Cr(VI)] causes a major reduction in yield and quality of crops worldwide. The root is the first plant organ that interacts with Cr(VI) toxicity, which inhibits primary root elongation, but the underlying mechanisms of this inhibition remain elusive. In this study, we investigate the possibility that Cr(VI) reduces primary root growth of Arabidopsis by modulating the cell cycle-related genes and that ethylene signalling contributes to this process. We show that Cr(VI)-mediated inhibition of primary root elongation was alleviated by the ethylene perception and biosynthesis antagonists silver and cobalt, respectively. Furthermore, the ethylene signalling defective mutants (ein2-1 and etr1-3) were insensitive, whereas the overproducer mutant (eto1-1) was hypersensitive to Cr(VI). We also report that high levels of Cr(VI) significantly induce the distribution and accumulation of auxin in the primary root tips, but this increase was significantly suppressed in seedlings exposed to silver or cobalt. In addition, genetic and physiological investigations show that AUXIN-RESISTANT1 (AUX1) participates in Cr(VI)-induced inhibition of primary root growth. Taken together, our results indicate that ethylene mediates Cr(VI)-induced inhibition of primary root elongation by increasing auxin accumulation and polar transport by stimulating the expression of AUX1.

The SPATULA transcription factor regulates seed oil content by controlling seed specific genes in Arabidopsis thaliana

Seed oil content, as a key economical trait, is influenced by multiple factors during seed development. Recent studies have established that control of seed development and seed oil content are interrelated process, controlled by transcription factors. Previously, a bHLH transcription factor SPATULA was reported to have pleiotropic effect on various organ development including root, leaf, and siliques but not seed development. Here, our results demonstrated a novel function of SPATULA to regulate seed size and seed fatty acids (FAs) content in Arabidopsis. The loss function of SPATULA significantly increased seed size, reduced seed FAs content. On the contrary, overexpression of SPATULA significantly increased the fatty acid contents without changing seed size. Ultrastructure analysis revealed that modification of seed FAs content by SPATULA was mainly through alteration of aleurone grain in seed embryo cells. Gene expression analyses provide a brief overview on the effects of SPATULA on key genes implicated in seed FAs content. These results demonstrated the SPATULA promotes fatty acid accumulation through inhibition of seed storage protein associate gene and induction of fatty acid associate genes during seed development in Arabidopsis. Our study had further extended the knowledge of SPATULA function, and it can provide new genetic resource for oil crop modification in Brassicaceae.

Linkage Mapping of Stem Saccharification Digestibility in Rice.

Rice is the staple food of almost half of the world population, and in excess 90% of it is grown and consumed in Asia, but the disposal of rice straw poses a problem for farmers, who often burn it in the fields, causing health and environmental problems. However, with increased focus on the development of sustainable biofuel production, rice straw has been recognized as a potential feedstock for non-food derived biofuel production. Currently, the commercial realization of rice as a biofuel feedstock is constrained by the high cost of industrial saccharification processes needed to release sugar for fermentation. This study is focused on the alteration of lignin content, and cell wall chemotypes and structures, and their effects on the saccharification potential of rice lignocellulosic biomass. A recombinant inbred lines (RILs) population derived from a cross between the lowland rice variety IR1552 and the upland rice variety Azucena with 271 molecular markers for quantitative trait SNP (QTS) analyses was used. After association analysis of 271 markers for saccharification potential, 1 locus and 4 pairs of epistatic loci were found to contribute to the enzymatic digestibility phenotype, and an inverse relationship between reducing sugar and lignin content in these recombinant inbred lines was identified. As a result of QTS analyses, several cell-wall associated candidate genes are proposed that may be useful for marker-assisted breeding and may aid breeders to produce potential high saccharification rice varieties.

PIL5 represses floral transition in Arabidopsis under long day conditions

PHYTOCHROME INTERACING FACTOR 3 LIKE 5 (PIL5), also named PHYTOCHROME INTERACTING FACTOR 1 (PIF1) is an important b-HLH transcription factor in Arabidopsis thaliana. Here we show that mutant of pil5-1 displays early flowering phenotype. We demonstrate that the expressions of the major flowering promoter genes [FLOWERING LOCUS T (FT), SUPPRESOR OF OVEREXPRESSION OF CO 1 (SOC1), and LEAFY (LFY)] are upregulated in the mutant of pil5-1. There is a significant increase of the mRNA of PIL5 in the mutants of co2-1, ft-10, soc1-2, and lfy-4. These changes provide the molecular evidence that PIL5 interacts with the flowering regulators to control flowering time. Moreover, it is shown in our results that PIL5 mutation mediates the increased contents of gibberellic acid (GA). Which is further supported by the qRT-PCR analysis, an increased transcriptome level of the GA biosynthesis genes (GA3ox1, GA3ox2, GA20ox1, GA20ox2, and GA20ox3) has been observed in the pil5-1 mutants as compared to the wild type. Collectively, PIL5 is involved in floral transition interacting with flowering integrators and GA.