Discovery and molecular characterization of a novel trichovirus infecting sweet cherry.

Contigs with the highest sequence similarity (73%) to Apricot pseudo-chlorotic leaf spot virus (genus Trichovirus, family Betaflexiviridae) were identified by high-throughput sequencing from a symptomless sweet cherry accession. The complete genome sequence of this new virus is 7460 nucleotides, excluding the 3' poly(A) tail. Its genome organization is very similar to several trichoviruses infecting fruit trees, with three open reading frames encoding putative replicase, movement protein and coat protein (CP). The virus shares amino acid sequence identities of 60-73% at replicase and 53-76% at CP with other trichoviruses. Phylogenetic analyses group it and other trichoviruses in a cluster. These results support that this virus, which is tentatively named cherry latent virus 1, should be considered a new member in the genus Trichovirus.

Manipulation of two α-endo-ß-1,4-glucanase genes, AtCel6 and GmCel7, reduces susceptibility to Heterodera glycines in soybean roots.

Plant endo-ß-1,4-glucanases (EGases) include cell wall-modifying enzymes that are involved in nematode-induced growth of syncytia (feeding structures) in nematode-infected roots. EGases in the α- and ß-subfamilies contain signal peptides and are secreted, whereas those in the γ-subfamily have a membrane-anchoring domain and are not secreted. The Arabidopsis α-EGase At1g48930, designated as AtCel6, is known to be down-regulated by beet cyst nematode (Heterodera schachtii) in Arabidopsis roots, whereas another α-EGase, AtCel2, is up-regulated. Here, we report that the ectopic expression of AtCel6 in soybean roots reduces susceptibility to both soybean cyst nematode (SCN; Heterodera glycines) and root knot nematode (Meloidogyne incognita). Suppression of GmCel7, the soybean homologue of AtCel2, in soybean roots also reduces the susceptibility to SCN. In contrast, in studies on two γ-EGases, both ectopic expression of AtKOR2 in soybean roots and suppression of the soybean homologue of AtKOR3 had no significant effect on SCN parasitism. Our results suggest that secreted α-EGases are likely to be more useful than membrane-bound γ-EGases in the development of an SCN-resistant soybean through gene manipulation. Furthermore, this study provides evidence that Arabidopsis shares molecular events of cyst nematode parasitism with soybean, and confirms the suitability of the Arabidopsis-H. schachtii interaction as a model for the soybean-H. glycines pathosystem.

Arabidopsis genes, AtNPR1, AtTGA2 and AtPR-5, confer partial resistance to soybean cyst nematode (Heterodera glycines) when overexpressed in transgenic soybean roots.

BACKGROUND: Extensive studies using the model system Arabidopsis thaliana to elucidate plant defense signaling and pathway networks indicate that salicylic acid (SA) is the key hormone triggering the plant defense response against biotrophic and hemi-biotrophic pathogens, while jasmonic acid (JA) and derivatives are critical to the defense response against necrotrophic pathogens. Several reports demonstrate that SA limits nematode reproduction. RESULTS: Here we translate knowledge gained from studies using Arabidopsis to soybean. The ability of thirty-one Arabidopsis genes encoding important components of SA and JA synthesis and signaling in conferring resistance to soybean cyst nematode (SCN: Heterodera glycines) are investigated. We demonstrate that overexpression of three of thirty-one Arabidoposis genes in transgenic soybean roots of composite plants decreased the number of cysts formed by SCN to less than 50% of those found on control roots, namely AtNPR1(33%), AtTGA2 (38%), and AtPR-5 (38%). Three additional Arabidopsis genes decreased the number of SCN cysts by 40% or more: AtACBP3 (53% of the control value), AtACD2 (55%), and AtCM-3 (57%). Other genes having less or no effect included AtEDS5 (77%), AtNDR1 (82%), AtEDS1 (107%), and AtPR-1 (80%), as compared to control. Overexpression of AtDND1 greatly increased susceptibility as indicated by a large increase in the number of SCN cysts (175% of control). CONCLUSIONS: Knowledge of the pathogen defense system gained from studies of the model system, Arabidopsis, can be directly translated to soybean through direct overexpression of Arabidopsis genes. When the genes, AtNPR1, AtGA2, and AtPR-5, encoding specific components involved in SA regulation, synthesis, and signaling, are overexpressed in soybean roots, resistance to SCN is enhanced. This demonstrates functional compatibility of some Arabidopsis genes with soybean and identifies genes that may be used to engineer resistance to nematodes.

Modification of the expression of two NPR1 suppressors, SNC1 and SNI1, in soybean confers partial resistance to the soybean cyst nematode, Heterodera glycines.

Systemic acquired resistance (SAR) is an enhanced defence response triggered when plants detect a pathogen. The response is extended to uninfected organs to protect against future attack. NPR1 is a nuclear leucine-rich repeat protein with a key role in SAR. It binds specifically to salicylic acid, and acts as a transcriptional coregulator of SAR activators and an inhibitor of transcriptional repressors. The proteins encoded by Suppressor of NPR1, Constitutive (SNC1) and Suppressor of NPR1, Inducible (SNI1) interact with NPR1 to regulate the expression of pathogenesis-related genes. The Arabidopsis thaliana (L.) Heynh. snc1 mutant exhibits a constitutive resistance response, but in the sni1 mutant, the SNI1 protein is rendered incapable of suppressing pathogen resistance genes. To study the influence of SNC1 and SNI1 on resistance to the soybean cyst nematode (Heterodera glycines), soybean (Glycine max (L.) Merr.) roots were separately transformed with four constructs designed to: (i) overexpress GmSNC1, the soybean orthologue of AtSNC1; (ii) overexpress AtSNI1; (iii) silence GmSNC1 and (iv) silence GmSNI1. A significant reduction of the female nematode population was observed in Treatments (i) and (iv). The expression of SAR marker genes was analysed in these treatments. The unusual pattern of expression of pathogen resistance genes shows there are differences in the effect resistance genes have on soybean and A. thaliana. Although NPR1 is involved in the cross-talk between the salicylic acid, jasmonic acid and ethylene pathways, understanding the nematode resistance mechanism in plants is still imprecise. These results provide further insights into the soybean defence response.

Ectopic expression of AtPAD4 broadens resistance of soybean to soybean cyst and root-knot nematodes.

BACKGROUND: The gene encoding PAD4 (PHYTOALEXIN-DEFICIENT4) is required in Arabidopsis for expression of several genes involved in the defense response to Pseudomonas syringae pv. maculicola. AtPAD4 (Arabidopsis thaliana PAD4) encodes a lipase-like protein that plays a regulatory role mediating salicylic acid signaling. RESULTS: We expressed the gene encoding AtPAD4 in soybean roots of composite plants to test the ability of AtPAD4 to deter plant parasitic nematode development. The transformed roots were challenged with two different plant parasitic nematode genera represented by soybean cyst nematode (SCN; Heterodera glycines) and root-knot nematode (RKN; Meloidogyne incognita). Expression of AtPAD4 in soybean roots decreased the number of mature SCN females 35 days after inoculation by 68 percent. Similarly, soybean roots expressing AtPAD4 exhibited 77 percent fewer galls when challenged with RKN. CONCLUSIONS: Our experiments show that AtPAD4 can be used in an economically important crop, soybean, to provide a measure of resistance to two different genera of nematodes.

Engineered resistance and hypersusceptibility through functional metabolic studies of 100 genes in soybean to its major pathogen, the soybean cyst nematode.

During pathogen attack, the host plant induces genes to ward off the pathogen while the pathogen often produces effector proteins to increase susceptibility of the host. Gene expression studies of syncytia formed in soybean root by soybean cyst nematode (Heterodera glycines) identified many genes altered in expression in resistant and susceptible roots. However, it is difficult to assess the role and impact of these genes on resistance using gene expression patterns alone. We selected 100 soybean genes from published microarray studies and individually overexpressed them in soybean roots to determine their impact on cyst nematode development. Nine genes reduced the number of mature females by more than 50 % when overexpressed, including genes encoding ascorbate peroxidase, ß-1,4-endoglucanase, short chain dehydrogenase, lipase, DREPP membrane protein, calmodulin, and three proteins of unknown function. One gene encoding a serine hydroxymethyltransferase decreased the number of mature cyst nematode females by 45 % and is located at the Rhg4 locus. Four genes increased the number of mature cyst nematode females by more than 200 %, while thirteen others increased the number of mature cyst nematode females by more than 150 %. Our data support a role for auxin and ethylene in susceptibility of soybean to cyst nematodes. These studies highlight the contrasting gene sets induced by host and nematode during infection and provide new insights into the interactions between host and pathogen at the molecular level. Overexpression of some of these genes result in a greater decrease in the number of cysts formed than recognized soybean cyst nematode resistance loci.

Sulfate reduction and copper precipitation by a Citrobacter sp. isolated from a mining area.

A strain of sulfate-reducing bacteria, designated strain 'DBM', was isolated from sediments of a mining area. Phylogenetic analysis of the 16S rRNA gene sequence of the isolate revealed that it was related to members of the genus Citrobacter, with C. AzoR-4, C. freundii, C. braakii and C. werkmanii being the most closely related species (sequence similarity up to 98%). Few studies have been done on sulfate reduction ability in Citrobacter. Electron microscopy studies showed that the morphology of the strain DBM was rod-shaped. Strain DBM reduced 10mM of sulfate completely to sulfide within 7d, and it recovered its sulfate reduction ability after 7d of aerobic growth. Furthermore, strain DBM effectively precipitated 0.40 mM copper during its growth. Elemental composition of the resulting microbial precipitate was studied using electro-dispersive X-ray spectroscopy, and it was found that the ratio of S:Cu was 1.07. The result was consistent with the formation of copper sulfide. Heavy metal precipitation by Citrobacter sp. strain DBM was a phenomenon that may be useful in the bioremediation of acid mine drainage.

Photocatalytic activity of polymer-modified ZnO under visible light irradiation.

Photocatalytic removal of phenol, rhodamine B, and methyl orange was studied using the photocatalyst ZnO/poly-(fluorene-co-thiophene) (PFT) under visible light. After 2 h irradiation with three 1 W LED (light-emitting diode) lights, about 40% removal of both phenol and methyl orange was achieved; rhodamine B was completely degraded to rhodamine. Diffuse reflectance spectra showed that the absorbance range of PFT/ZnO was expanded from 387 nm (ZnO) to about 500 nm. Photoluminescent spectra and photoluminescent quantum efficiency indicated that electrons were transferred from PFT to the conduction band of ZnO. Electron spin resonance (ESR) signals of spin-trapped paramagnetic species with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) evidenced that the OH* radicals were indeed formed in the PFT/ZnO system under visible light irradiation. A working mechanism involving excitation of PFT, followed by charge injection into the ZnO conduction band is proposed.

Zinc hyperaccumulation and uptake by Potentilla griffithii Hook.

The ability of Potentilla griffithii Hook var. velutina Cardot to hypaeraccumulate zinc (Zn) was identified through field survey and hydroponic experiments. Our results showed that P. griffithii could be classified as a new Zn hyperaccumulator. Zn concentrations in the shoots of P. griffithii averaged 6250 mg kg(-1) (3870-8530 mg kg(-1)) growing in Zn-rich soils. The highest Zn concentration was observed in the leaves of P. griffithii at 22,990 mg kg(-1). The fact that P. griffithii was able to grow in a mining soil with a Zn concentration of 193,000 mg kg(-1) without showing a major sign of phytotoxicity demonstrated its high tolerance to Zn. When growing in hydroponic systems, P. griffithii accumulated a maximum 26700 mg kg(-1) zinc concentration in the shoots, indicating the ability of this species to effectively take up and translocate Zn. Translocation factors (the ratio of Zn concentration in shoot to root) of 1.1 to 1.6 were obtained. Compared to the control, dry biomass of P. griffithii in 160 mg L(-1) Zn treatment increased 66.6% (P < 0.05). The time-course experiment showed that the maximum Zn concentration at 100 mg L(-1) Zn treatment was found at 16 d, much later than that of the 10 mg L(-1) Zn treatment, which might be an attribution of a accumulating mechanism or detoxification of a plant. The report of a new Zn hyperaccumulator provides a new plant species for the phytoremediation of contaminated soil and for the research on mechanisms of Zn hyperaccumulation in plants.

Using hyperaccumulator plants to phytoextract soil Ni and Cd.

Two strategies of phytoextraction have been shown to have promise for practical soil remediation: domestication of natural hyperaccumulators and bioengineering plants with the genes that allow natural hyperaccumulators to achieve useful phytoextraction. Because different elements have different value, some can be phytomined for profit and others can be phytoremediated at lower cost than soil removal and replacement. Ni phytoextraction from contaminated or mineralized soils offers economic return greater than producing most crops, especially when considering the low fertility or phytotoxicity of Ni rich soils. Only soils that require remediation based on risk assessment will comprise the market for phytoremediation. Improved risk assessment has indicated that most Zn + Cd contaminated soils will not require Cd phytoextraction because the Zn limits practical risk from soil Cd. But rice and tobacco, and foods grown on soils with Cd contamination without corresponding 100-fold greater Zn contamination, allow Cd to readily enter food plants and diets. Clear evidence of human renal tubular dysfunction from soil Cd has only been obtained for subsistence rice farm families in Asia. Because of historic metal mining and smelting, Zn + Cd contaminated rice soils have been found in Japan, China, Korea, Vietnam and Thailand. Phytoextraction using southern France populations of Thlaspi caerulescens appears to be the only practical method to alleviate Cd risk without soil removal and replacement. The southern France plants accumulate 10-20-fold higher Cd in shoots than most T. caerulescens populations such as those from Belgium and the UK. Addition of fertilizers to maximize yield does not reduce Cd concentration in shoots; and soil management promotes annual Cd removal. The value of Cd in the plants is low, so the remediation service must pay the costs of Cd phytoextraction plus profits to the parties who conduct phytoextraction. Some other plants have been studied for Cd phytoextraction, but annual removals are much lower than the best T. caerulescens. Improved cultivars with higher yields and retaining this remarkable Cd phytoextraction potential are being bred using normal plant breeding techniques.