Selective trans-Cinnamic Acid Uptake Impairs [Ca2+]cyt Homeostasis and Growth in Cucumis sativus L.

To obtain insight into interspecies interactions mediated by allelochemicals, the response of cucumber (Cucumis sativus L. cv Jinyan No.4) and figleaf gourd (Cucurbita ficifolia Bouché) seedlings to trans-cinnamic acid (CA) (1) was investigated. While trans-CA is an autotoxin in cucumber root exudates, figleaf gourd is resistant to it. Cucumber, however, had a high rate of trans-CA uptake by the roots, leading to reduced root growth. The trans-CA treatment also resulted in an intracellular release of Ca²⁺ from the vacuole to the cytoplasm, and, thus, an increased [Ca²⁺]_cyt level accompanied by gradual loss of cell viability in cucumber roots. Taken together, these results suggest that [Ca²⁺]_cyt homeostatic disturbance is one of the primary triggers for trans-CA phytotoxicity in cucumber.     

A Truncated TIR-NBS Protein TN10 Pairs with Two Clustered TIR-NBS-LRR Immune Receptors and Contributes to Plant Immunity in Arabidopsis

The encoding genes of plant intracellular nucleotide-binding site (NBS) and leucine-rich repeat (LRR) domain receptors (NLRs) often exist in the form of a gene cluster. Several recent studies demonstrated that the truncated Toll/interleukin-1 receptor-NBS (TIR-NBS) proteins play important roles in immunity. In this study, we identified a large TN gene cluster on Arabidopsis ecotype Col-0 chromosome 1, which included nine TN genes, TN4 to TN12. Interestingly, this cluster also contained two typical TIR-NBS-LRR genes: At1g72840 and At1g72860 (hereinafter referred to as TNL40 and TNL60, respectively), which formed head-to-head genomic arrangement with TN4 to TN12. However, the functions of these TN and TNL genes in this cluster are still unknown. Here, we showed that the TIR domains of both TNL40 and TNL60 associated with TN10 specifically. Furthermore, both TNL40TIR and TNL60TIR induced cell death in Nicotiana tabacum leaves. Subcellular localization showed that TNL40 mainly localized in the cytoplasm, whereas TNL60 and TN10 localized in both the cytoplasm and nucleus. Additionally, the expression of TNL40, TNL60, and TN10 were co-regulated after inoculated with bacterial pathogens. Taken together, our study indicates that the truncated TIR-NBS protein TN10 associates with two clustered TNL immune receptors, and may work together in plant disease resistance     

The Rice Cation/H+ Exchanger Family Involved in Cd Tolerance and Transport

Cadmium (Cd), a heavy metal toxic to humans, easily accumulates in rice grains. Rice with unacceptable Cd content has become a serious food safety problem in many rice production regions due to contaminations by industrialization and inappropriate waste management. The development of rice varieties with low grain Cd content is seen as an economic and long-term solution of this problem. The cation/H⁺ exchanger (CAX) family has been shown to play important roles in Cd uptake, transport and accumulation in plants. Here, we report the characterization of the rice CAX family. The six rice CAX genes all have homologous genes in Arabidopsis thaliana. Phylogenetic analysis identified two subfamilies with three rice and three Arabidopsis thaliana genes in both of them. All rice CAX genes have trans-member structures. OsCAX1a and OsCAX1c were localized in the vacuolar while OsCAX4 were localized in the plasma membrane in rice cell. The consequences of qRT-PCR analysis showed that all the six genes strongly expressed in the leaves under the different Cd treatments. Their expression in roots increased in a Cd dose-dependent manner. GUS staining assay showed that all the six rice CAX genes strongly expressed in roots, whereas OsCAX1c and OsCAX4 also strongly expressed in rice leaves. The yeast (Saccharomyces cerevisiae) cells expressing OsCAX1a, OsCAX1c and OsCAX4 grew better than those expressing the vector control on SD-Gal medium containing CdCl₂. OsCAX1a and OsCAX1c enhanced while OsCAX4 reduced Cd accumulation in yeast. No auto-inhibition was found for all the rice CAX genes. Therefore, OsCAX1a, OsCAX1c and OsCAX4 are likely to involve in Cd uptake and translocation in rice, which need to be further validated.     

CsCDPK6, a CsSAMS1-Interacting Protein,Affects Polyamine/Ethylene Biosynthesis in Cucumber and Enhances Salt Tolerance by Overexpression in Tobacco

S-adenosylmethionine synthetase (SAMS) plays a crucial role in regulating stress responses. In a recent study, we found that overexpression of the cucumber gene CsSAMS1 in tobacco can affect the production of polyamines and ethylene, as well as enhancing the salt stress tolerance of tobacco, but the exact underlying mechanisms are elusive. The calcium-dependent protein kinase (CDPK) family is ubiquitous in plants and performs different biological functions in plant development and response to abiotic stress. We used a yeast two-hybrid system to detect whether the protein CDPK6 could interact with SAMS1 and verified their interaction by bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation (Co-IP) assays. To further explore the function of cucumber CDPK6, we isolated and characterized CsCDPK6 in cucumber. CsCDPK6 is a membrane protein that is highly expressed under various abiotic stresses, including salt stress. It was also observed that ectopic overexpression of CsCDPK6 in tobacco enhanced salt tolerance. Under salt stress, CsCDPK6-overexpressing lines enhanced the survival rate and reduced stomatal apertures in comparison to wild-type (WT) lines, as well as lowering malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents and causing less relative electrolyte leakage. Moreover, repression of CsCDPK6 expression by virus-induced gene silencing (VIGS) in cucumber seedling cotyledons under salt stress increased ethylene production and promoted the transformation from putrescine (Put) to spermidine (Spd) and spermine (Spm). These findings shed light on the interaction of CsSAMS1 and CsCDPK6, which functions positively to regulate salt stress in plants.     

A study of hydroxyethyl imidazoline as H2S corrosion inhibitor using electrochemical noise and electrochemical impedance spectroscopy

A study of H₂S corrosion inhibition of pipeline steel by hydroxyethyl imidazoline has been carried out by using electrochemical techniques. Inhibitor concentration included 5, 10, 25, 50, and 100 ppm in a H₂S-containing 3% NaCl solution at 50 °C. Techniques included linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and electrochemical noise (EN) measurements. In addition to the traditional noise in voltage and current, noise resistance (R _n) measurements were used. All techniques showed that the most efficient inhibitor concentration was between 5 and 10 ppm, but inhibitor efficiency decreased after 8 h of testing. Furthermore, EN measurements showed that steel was highly susceptible to localized corrosion at inhibitor doses lower than 10 ppm due to the establishment of a porous inhibitor film. However, with 50 or 100 ppm of inhibitor, the steel was susceptible to a mixture of uniform and localized corrosion. Hurst exponent was higher in presence of inhibitor for times shorter than 8 h, indicating a short residence time of the inhibitor. The data could not be fitted to any adsorption isotherm model, indicating a lack of strong adsorption of the inhibitor to the metal surface.     

A Novel Allele Encoding 7-Hydroxymethyl Chlorophyll a Reductase Confers Bacterial Blight Resistance in Rice

Rice spotted leaf mutants are helpful to investigate programmed cell death (PCD) and defense response pathways in plants. Using a map-based cloning strategy, we characterized novel rice spotted leaf mutation spl^HM143 that encodes a 7-hydroxymethyl chlorophyll a reductase (OsHCAR). The wild-type (WT) allele could rescue the mutant phenotype, as evidenced by complementation analysis. OsHCAR was constitutively expressed at all rice tissues tested and its expression products localized to chloroplasts. The mutant exhibited PCD and leaf senescence with increased H₂O₂ (hydrogen peroxide) accumulation, increased of ROS (reactive oxygen species) scavenging enzymes activities and TUNEL (terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling) -positive nuclei, upregulation of PCD related genes, decreased chlorophyll (Chl) contents, downregulation of photosynthesis-related genes, and upregulation of senescence-associated genes. Besides, the mutant exhibited enhanced bacterial blight resistance with significant upregulation of defense response genes. Knockout lines of OsHCAR exhibited spotted leaf phenotype, cell death, leaf senescence, and showed increased resistance to the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) coupled with upregulation of five pathogenesis-related marker genes. The overexpression of OsHCAR resulted in increased susceptibility to Xoo with decreased expression of pathogenesis-related marker genes. Altogether, our findings revealed that OsHCAR is involved in regulating cell death and defense response against bacterial blight pathogen in rice.     

ZmCIPK21, A Maize CBL-Interacting Kinase,Enhances Salt Stress Tolerance in Arabidopsis thaliana

Salt stress represents an increasing threat to crop growth and yield in saline soil. In this study, we identified a maize calcineurin B-like protein-interacting protein kinase (CIPK), ZmCIPK21, which was primarily localized in the cytoplasm and the nucleus of cells and displayed enhanced expression under salt stress. Over-expression of ZmCIPK21 in wild-type Arabidopsis plants increased their tolerance to salt, as supported by the longer root lengths and improved growth. The downstream stress-response genes, including dehydration-responsive element-binding (DREB) genes were also activated in transgenic plants over-expressing ZmCIPK21. In addition, introduction of the transgenic ZmCIPK21 gene into the Arabidopsis mutant cipk1-2 rescued the salt-sensitive phenotype under high salt stress. Measurement of Na⁺ and K⁺ content in transgenic plants showed that over-expression of ZmCIPK21 decreased accumulation of Na⁺ and allowed retention of relatively high levels of K⁺, thereby enhancing plant tolerance to salt conditions.     

Molecular Dissection of the Gene OsGA2ox8 Conferring Osmotic Stress Tolerance in Rice

Gibberellin 2-oxidase (GA2ox) plays an important role in the GA catabolic pathway and the molecular function of the OsGA2ox genes in plant abiotic stress tolerance remains largely unknown. In this study, we functionally characterized the rice gibberellin 2-oxidase 8 (OsGA2ox8) gene. The OsGA2ox8 protein was localized in the nucleus, cell membrane, and cytoplasm, and was induced in response to various abiotic stresses and phytohormones. The overexpression of OsGA2ox8 significantly enhanced the osmotic stress tolerance of transgenic rice plants by increasing the number of osmotic regulators and antioxidants. OsGA2ox8 was differentially expressed in the shoots and roots to cope with osmotic stress. The plants overexpressing OsGA2ox8 showed reduced lengths of shoots and roots at the seedling stage, but no difference in plant height at the heading stage was observed, which may be due to the interaction of OsGA2ox8 and OsGA20ox1, implying a complex feedback regulation between GA biosynthesis and metabolism in rice. Importantly, OsGA2ox8 was able to indirectly regulate several genes associated with the anthocyanin and flavonoid biosynthetic pathway and the jasmonic acid (JA) and abscisic acid (ABA) biosynthetic pathway, and overexpression of OsGA2ox8 activated JA signal transduction by inhibiting the expression of jasmonate ZIM domain-containing proteins. These results provide a basis for a future understanding of the networks and respective phenotypic effects associated with OsGA2ox8.