Raman imaging of cell wall polymers in Arabidopsis thaliana

We present chemical images of Arabidopsis thaliana stem cross-sections acquired by confocal Raman microscopy. Using green light (532 nm) from a continuous wave laser, the spatial distributions of cell wall polymers in Arabidopsis are visualized for the first time with lateral resolution that is sub-μm. Our results facilitate the label-free in situ characterization and screening of cell wall composition in this plant biology and genetics model organism, contributing ultimately towards an understanding of the molecular biology of many plant traits.     

ELONGATA3 is required for shoot meristem cell cycle progression in Arabidopsis thaliana seedlings

A key feature of the development of a higher plant is the continuous formation of new organs from the meristems. Originally patterned during embryogenesis, the meristems must activate cell division de novo at the time of germination, in order to initiate post-embryonic development. In a mutagenesis screen aimed at finding new players in early seedling cell division control, we identified ELONGATA3 (ELO3) as a key regulator of meristem cell cycle activation in Arabidopsis. Our results show that plants carrying a hypomorphic allele of ELO3 fail to activate cell division in the meristems following germination, which leads to seedling growth arrest and lethality. Further analyses suggest that this is due to a failure in DNA replication, followed by cell cycle arrest, in the meristematic tissue. Interestingly, the meristem cell cycle arrest in elo3 mutants, but not the later leaf developmental defects that have been linked to the loss of ELO3 activities, can be relieved by the addition of metabolic sugars in the growth medium. This finding points to a new role by which carbohydrate availability promotes meristem growth. Furthermore, growth arrested elo3 mutants suffer a partial loss of shoot meristem identity, which provides further evidence that cell cycle activities can influence the control of tissue identity.     

The MIXTA-like Transcription factor MYB16 is a major regulator of cuticle formation in vegetative organs

Cuticle secreted on the surface of the epidermis of aerial organs protects plants from the external environment. We recently found that Arabidopsis MIXTA-like R2R3-MYB family members MYB16 and MYB106 regulate cuticle formation in reproductive organs and trichomes. However, the artificial miRNA (amiRNA)-mediated knockdown plants showed no clear phenotypic abnormality in vegetative tissues. In this study, we used RNA interference (RNAi) targeting MYB16 to produce plants with reduced expression of both MYB16 and MYB106. The rosette leaves of RNAi plants showed more severe permeable cuticle phenotypes than the myb106 mutants expressing the MYB16 amiRNA in the previous study. The RNAi plants also showed reduced expression of cuticle biosynthesis genes LACERATA and ECERIFERUM1. By contrast, expression of a gain-of-function MYB16 construct induced over-accumulation of waxy substances on leaves. These results suggest that MYB16 functions as a major regulator of cuticle formation in vegetative organs, in addition to its effect in reproductive organs and trichomes.     

Inflorescence abnormalities occur with overexpression of Arabidopsis lyrata FT in the fwa mutant of Arabidopsis thaliana

Arabidopsis thaliana is a quantitative long-day plant with the timing of the floral transition being regulated by both endogenous signals and multiple environmental factors. fwa is a late-flowering mutant, and this phenotype is due to ectopic FWA expression caused by hypomethylation at the FWA locus. The floral transition results in the activation of the floral development process, the key regulators being the floral meristem identity genes, AP1 (APETALA1) and LFY (LEAFY). In this study, we describe inflorescence abnormalities in plants overexpressing the Arabidopsis lyrata FT (AlFT) and A. thaliana FWA (AtFWA) genes simultaneously. The inflorescence abnormality phenotype was present in only a proportion of plants. All plants overexpressing both AlFT and AtFWA flowered earlier than fwa, suggesting that the inflorescence abnormality and earlier flowering time are caused independently. The inflorescence abnormality phenotype was similar to that of the double mutant of ap1 and lfy, and AP1 and LFY genes were down-regulated in the abnormal inflorescences. From these results, we suggest that not only does ectopic AtFWA expression inhibit AtFT/AlFT function to delay flowering but that overexpression of AtFWA and AlFT together inhibits AP1 and LFY function to produce abnormal inflorescences.     

Fatty acid desaturase-6 (Fad6) is required for salt tolerance in Arabidopsis thaliana

Fatty acid desaturases play important role in plant responses to abiotic stresses including cold, high temperature, drought, and osmotic stress. In this work, we provide the evidence that Fad6, a chloroplast desaturase, is required for salt tolerance during the early seedling development of Arabidopsis. Expression of Fad6 was responsive to salt and osmotic stress. Compared with the wild-type plants, the fad6 mutant showed reduced tolerance to salt stress, and accumulated more Na⁺ and less K⁺ under high NaCl stress condition. Furthermore, cellular oxidative damage was more severe in fad6 when treated with high concentrations of NaCl, as indicated by increased electrolyte leakage rate and malondialdehyde production, as well as by decreased activities of anti-oxidative enzymes. All these results suggest that Fad6 is required for salt resistance in Arabidopsis.     

Quercetin-induced H2O2 mediates the pathogen resistance against Pseudomonas syringae pv. Tomato DC3000 in Arabidopsis thaliana

Quercetin is a potent antioxidant and has been extensively used as a therapy intervention to prevent age-associated diseases. However, emerging studies showed it can also act as a prooxidant and induce H₂O₂ under certain conditions. In the current study, our results showed that quercetin contributed to the pathogen resistance in Arabidopsis thaliana (Arabidopsis) in response to the infection of virulent strain Pseudomonas syringae pv. Tomato DC3000 (Pst). Various defense responses, such as H₂O₂ burst, callose deposition, cell death, PR1 (pathogenesis-related 1) and PAL1 (Phe ammonia-lyase 1) gene expression, have been investigated in quercetin-pretreated Pst-inoculated Arabidopsis Col-0 and there was a strong defensive response in quercetin-pretreated Arabidopsis against virulent Pst. However, with the presence of catalase, the protective effects of quercetin on pathogen resistance to virulent Pst disappeared in Arabidopsis, suggesting that H₂O₂ may play a key role in plant defense responses. In addition, we confirmed that quercetin did not show any beneficial effect on pathogen-free leaves in Arabidopsis, indicating that pathogen challenge is also required to induce the defense responses in quercetin-pretreated Arabidopsis. Furthermore, strong defense responses have been observed in quercetin-pretreated Arabidopsis mutant jar1, ein2, and abi1-2 under Pst challenge, whereas no protective effect has been observed in quercetin-pretreated Arabidopsis mutant NahG and npr1. These findings indicate that quercetin induces the resistance to Pst in Arabidopsis via H₂O₂ burst and involvement of SA and NPR1.     

Metabolomics-oriented isolation and structure elucidation of 37 compounds including two anthocyanins from Arabidopsis thaliana

In order to conduct metabolomic studies in a model plant for genome research, such as Arabidopsis thaliana (Arabidopsis), it is a prerequisite to obtain structural information for the isolated metabolites from the plant of interest. In this study, we isolated metabolites of Arabidopsis in a relatively non-targeted way, aiming at the construction of metabolite standards and chemotaxonomic comparison. Anthocyanins (5 and 7) called A8 and A10 were isolated and their structures were elucidated as cyanidin 3-O-[2-O-(β-d-xylopyranosyl)-6-O-(4-O-(β-d-glucopyranosyl)-E-p-coumaroyl)-β-d-glucopyranoside]-5-O-[6-O-(malonyl)-β-d-glucopyranoside] and cyanidin 3-O-[2-O-(2-O-(E-sinapoyl)-β-d-xylopyranosyl)-6-O-(4-O-(β-d-glucopyranosyl)-E-p-coumaroyl)-β-d-glucopyranoside]-5-O-[β-d-glucopyranoside] from analyses of 1D NMR, 2D NMR (¹H NMR, NOE, ¹³C NMR, HMBC and HMQC), HRFABMS, FT-ESI-MS and GC-TOF-MS data. In addition, 35 known compounds, including six anthocyanins, eight flavonols, one nucleoside, one indole glucosinolate, four phenylpropanoids and a derivative, together with three indoles, one carotenoid, one apocarotenoid, three galactolipids, two chlorophyll derivatives, one steroid, one hydrocarbon, and two dicarboxylic acids, were also isolated and identified from their spectroscopic data.     

CIPK7 is involved in cold response by interacting with CBL1 in Arabidopsis thaliana

The family of calcineurin B-like (CBL) proteins is a unique group of Ca²⁺ sensors in plants. CBLs relay the calcium signal by interacting with and regulating the family of CBL-interacting protein kinases (CIPKs). Extensive studies have demonstrated that the CBL-CIPK complexes mediate plant responses to a variety of external stresses. However, there are few reports on the CBL-CIPK involved in cold stress responses. In this study, we analyzed expression of CIPK7 and CBL1 in Arabidopsis during cold treatments. Expression of CIPK7 was induced by cold, and CIPK7 interacted with CBL1 in vitro. Moreover, affinity chromatography purification of CIPK7 from Arabidopsis plants using CBL1 suggested that CIPK7 may associate with CBL1 in vivo. Expression of CBL1 was cold inducible, and CBL1 had a role in regulating cold response. By comparing expression patterns of CIPK7 between wild-type and cbl1 mutant plants, we found the induction of CIPK7 by cold stress was influenced by CBL1. This is the first report to demonstrate that CIPK7 may play a role in cold response via its interaction with CBL1.     

土霉素胁迫下拟南芥基因组DNA甲基化的MSAP分析

以拟南芥 (Arabidopsis thaliana)为材料,研究不同土霉素浓度下拟南芥幼苗生长发育及基因组DNA的甲基化水平和变化模式。结果表明,3、5、7\,9 μmol/L土霉素胁迫对拟南芥幼苗的根长和株高有显著抑制作用;但对拟南芥幼苗的侧根数量有显著促进作用。甲基化敏感扩增多态性 (methylation-sensitive amplification polymorphism, MSAP)分析表明,经3、5、7\,9 μmol/L土霉素处理后基因组DNA甲基化比率分别为17.91%、12.50%、11.81%和14.62%,均低于对照 (18.18%)。结果表明,拟南芥经土霉素胁迫后存在基于 DNA甲基化水平和模式改变的表观遗传变异,5-甲基胞嘧啶百分含量的变化无统一趋势或规律。与对照相比,3、5、7\,9 μmol/L土霉素胁迫下拟南芥幼苗基因组DNA的甲基化和去甲基化分别为13.29%、9.22%、8.03%、12.59%和2.80%、4.26％、5.11%、4.90％。由此推测,DNA甲基化可能是植物适应土霉素胁迫机制的机制之一。