Molecular mechanism of plant elicitor daphnetin-carboxymethyl chitosan nanoparticles against Ralstonia solanacearum by activating plant system resistance.

The exploration of biopolymer-based materials to avoid hazardous chemicals in agriculture has gained enormous importance for sustainable crop protection. Due to its good biocompatibility and water solubility, carboxymethyl chitosan (CMCS) has been widely applied as a pesticide carrier biomaterial. However, the mechanism by which carboxymethyl chitosan-grafted natural product nanoparticles induce tobacco systemic resistance against bacterial wilt remains largely unknown. In this study, water-soluble CMCS-grafted daphnetin (DA) nanoparticles (DA@CMCS-NPs) were successfully synthesized, characterized, and assessed for the first time. The grafting rate of DA in CMCS was 10.05 %, and the water solubility was increased. In addition, DA@CMCS-NPs significantly increased the activities of CAT, PPO and SOD defense enzymes, activated the expression of PR1 and NPR1, and suppressed the expression of JAZ3. DA@CMCS-NPs could induce immune responses against R. solanacearum in tobacco, including increases in defense enzymes and overexpression of pathogenesis-related (PR) proteins. The application of DA@CMCS-NPs effectively suppressed the development of tobacco bacterial wilt in pot experiments, and the control efficiency was as high as 74.23 %, 67.80 %, 61.67 % at 8, 10, and 12 days after inoculation. Additionally, DA@CMCS-NPs has excellent biosafety. Therefore, this study highlighted the application of DA@CMCS-NPs in manipulating tobacco to generate defense responses against R. solanacearum, which can be attributed to systemic resistance.

MAP30 and luffin-α: Novel ribosome-inactivating proteins induce plant systemic resistance against plant viruses.

Ribosome-inactivating proteins (RIPs) are toxic N-glycosylase that act on eukaryotic and prokaryotic rRNAs, resulting in arrest protein synthesis. RIPs are widely found in higher plant species and display strong antiviral activity. Previous studies have shown that PAP and α-MMC have antiviral activity against TMV. However, the localization of RIPs in plant cells and the mechanism by which RIPs activate plant defense against several plant viruses remain unclear. In this study, we obtained four RIPs (the C-terminal deletion mutant of pokeweed antiviral proteins (PAP-c), alpha-momorcharin (α-MMC), momordica anti-HIV protein of 30 kDa (MAP30) and luffin-α). The subcellular localization results indicated that these four RIPs were located on the plant cell membrane. Heterologous expression of RIPs (PAP-c, α-MMC, MAP30, luffin-α) enhanced tobacco mosaic virus (TMV) resistance in N. benthamiana. Compared with the control treatment, these RIPs significantly reduced the TMV content (149-357 fold) and altered the movement of TMV in the leaves of N. benthamiana. At the same time, heterologous expression of RIPs (MAP30 and luffin-α) could relieve TMV-induced oxidative damage, significantly inducing the expression of plant defense genes including PR1 and PR2. Furthermore, application of these RIPs could inhibit the infection of turnip mosaic virus (TuMV) and potato virus x (PVX). Therefore, this study demonstrated that MAP30 and luffin-α could be considered as new, effective RIPs for controlling plant viruses by activating plant systemic defense.

Plant secondary metabolite, daphnetin reduces extracellular polysaccharides production and virulence factors of Ralstonia solanacearum.

Plants deploy a variety of secondary metabolites to fend off pathogen attack. Certain plants could accumulate coumarins in response to infection of bacteria, fungi, virus and oomycetes. Although coumarins are generally considered toxic to microbes, the exact mechanisms are often unknown. Here, we showed that a plant secondary metabolite daphnetin functions primarily by inhibiting Ralstonia solanacearum extracellular polysaccharides (EPS) production and biofilm formation in vitro, through suppressing genes expression of xpsR, epsE, epsB and lexM. Indeed, daphnetin significantly impaired virulence of R. solanacearum on tobacco plants. Transcriptional analysis suggested that daphnetin suppresses EPS synthesis cluster genes expression through transcriptional regulator XpsR. And daphnetin alter mainly virulence factors genes involved in type III secretion system, and type IV secretion system. R. solanacearum lacking EPS synthesis genes (epsB and epsC) that do not produce EPS, showed less virulence on tobacco plants. Molecular docking results indicated that the critical residues of domain in the binding pocket of the EpsB protein interact with daphnetin via conventional hydrogen bonding and hydrophobic interactions. Collectively, we found that daphnetin has potential as a novel virulence inhibitor of R. solanacearum, directly regulates EPS synthesis genes expression.

Metabolic Profiling of Resistant and Susceptible Tobaccos Response Incited by Ralstonia pseudosolanacearum Causing Bacterial Wilt.

The causal agent of bacterial wilt, Ralstonia pseudosolanacearum, can cause significant economic losses during tobacco production. Metabolic analyses are a useful tool for the comprehensive identification of plant defense response metabolites. In this study, a gas chromatography-mass spectrometry (GC-MS) approach was used to identify metabolites differences in tobacco xylem sap in response to R. pseudosolanacearum CQPS-1 in two tobacco cultivars: Yunyan87 (susceptible to R. pseudosolanacearum) and K326 (quantitatively resistant). Metabolite profiling 7 days post inoculation with R. pseudosolanacearum identified 88 known compounds, 42 of them enriched and 6 depleted in the susceptible cultivar Yunyan87, while almost no changes occurred in quantitatively resistant cultivar K326. Putrescine was the most enriched compound (12-fold) in infected susceptible tobacco xylem, followed by methyl-alpha-d-glucopyranoside (9-fold) and arabinitol (6-fold). Other sugars, amino acids, and organic acids were also enriched upon infection. Collectively, these metabolites can promote R. pseudosolanacearum growth, as shown by the increased growth of bacterial cultures supplemented with xylem sap from infected tobacco plants. Comparison with previous metabolic data showed that beta-alanine, phenylalanine, and leucine were enriched during bacterial wilt in both tobacco and tomato xylem.

An increase in vascular endothelial growth factor (VEGF) and VEGF soluble receptor-1 (sFlt-1) are associated with early recurrent spontaneous abortion.

Recurrent spontaneous abortion (RSA) is a health problem that affects approximately 1% to 5% reproductive age woman. Yet, in around half of these patients, the mechanism for RSA is unexplained. Recent studies have indicated that placental ischemia/hypoxia and endothelial dysfunction are important factors in miscarriage. Other studies have indicated that the level and expression of soluble FMS-like tyrosine kinase-1 (sFlt1) is increased under a hypoxic environment. However, decreased sFlt-1 in the maternal circulation during the first trimester has recently been proposed as a potential marker for identifying risk of pregnancy loss. In this prospective study clinical samples were obtained within a short time after the fetal death, protein expression and maternal serum levels of sFlt1 were assessed and compared to samples taken from those with normal pregnancies. Our results indicate that levels of VEGF and sFlt-1 are both increased in women during early pregnancy compared women that are not pregnant (p<0.05) indicating that VEGF and sFlt-1 are both associated with pregnancy. More importantly, we detected a significant (p<0.05) increase in sFlt1 and VEGF levels and expression in the RSA patients who suffered subsequent miscarriages compare to controls. These results demonstrate that there is likely a relationship between VEGF, sFlt-1 and RSA suggesting that the high levels and over expression of sFlt-1 and VEGF might be associated with the pathogenesis of RSA.

Not every subseptate uterus requires surgical correction to reduce poor reproductive outcome.

OBJECTIVE: To evaluate whether hysteroscopic septoplasty should be performed in all women diagnosed with subseptate uterus. METHODS: In a prospective study, 138 patients diagnosed with subseptate uterus at the First Affiliated Hospital of Guangxi Medical University, Nanning, China, were enrolled between January 1, 2006, and March 1, 2011, and reproductive outcomes were compared among women who did and those who did not undergo hysteroscopic resection. Women were divided in 2 groups: group A comprised women with a history of recurrent spontaneous abortion (RSA), and was subdivided into control (A1) and surgery (A2) groups; group B comprised women with no history of poor reproductive outcomes, and was subdivided into control (B1) and surgery (B2) groups. RESULTS: The rates of pregnancy and term delivery were higher in group A2 than in group A1 (P<0.05). The incidence of RSA and preterm delivery was higher in group A1 than in group A2 (P<0.05). There was no difference in pregnancy rate, incidence of RSA, or preterm or term delivery between group B1 and group B2. CONCLUSION: Hysteroscopic septoplasty significantly improved pregnancy outcomes in women with a history of RSA, but did not influence reproductive outcomes in women with no history of poor pregnancy outcomes.