No abstract

Culture filtrates of a pathogenic isolate (IT37) of Stemphylium vesicarium, causing brown spot of European pear, induced veinal necrosis only on pear leaves susceptible to the pathogen. Two host-specific toxins, SV-toxins I and II, were purified from culture filtrates of IT37 by successively using Amberlite XAD-2 resin adsorption, cellulose thin-layer chromatography, and high-performance liquid chromatography under three different sets of conditions. Susceptible cultivars showed veinal necrosis at a SV-toxin I concentration of 0.01 to 0.1 mug/ml, whereas resistant cultivars were insensitive to the toxin at 1,000 mug/ml. SV-toxins I and II caused a dose-dependent increase in electrolyte loss from susceptible leaf tissues. No increase in electrolyte loss was detected in leaf tissues from resistant cultivars. The results of physiological studies indicated that SV-toxins appear to have an early effect on plasma membranes of susceptible leaves. Spores of a nonpathogenic isolate induced necrotic lesions on susceptible leaves in the presence of a small amount of toxin. SV-toxins were detected in intercellular fluids obtained from diseased leaves after inoculation with the pathogen. The results indicate that SV-toxins I and II produced by S. vesicarium can be characterized as host-specific toxins.

Groundnut Bud Necrosis Virus (GBNV) is a tripartite ambisense RNA plant virus that belongs to serogroup IV of Tospovirus genus. Non-Structural protein-m (NSm), which functions as movement protein in tospoviruses, is encoded by the M RNA. In this communication, we demonstrate that despite the absence of any putative transmembrane domain, GBNV NSm associates with membranes when expressed in E. coli as well as in N. benthamiana. Incubation of refolded NSm with liposomes ranging in size from 200–250 nm resulted in changes in the secondary and tertiary structure of NSm. A similar behaviour was observed in the presence of anionic and zwitterionic detergents. Furthermore, the morphology of the liposomes was found to be modified in the presence of NSm. Deletion of coiled coil domain resulted in the inability of in planta expressed NSm to interact with membranes. Further, when the C-terminal coiled coil domain alone was expressed, it was found to be associated with membrane. These results demonstrate that NSm associates with membranes via the C-terminal coiled coil domain and such an association may be important for movement of viral RNA from cell to cell.

No abstract

Plant viruses exploit the host machinery for targeting the viral genome-movement protein complex to plasmodesmata (PD). The mechanism by which the non-structural protein m (NSm) of Groundnut bud necrosis virus (GBNV) is targeted to PD was investigated using Agrobacterium mediated transient expression of NSm and its fusion proteins in Nicotiana benthamiana. GFP:NSm formed punctuate structures that colocalized with mCherry:plasmodesmata localized protein 1a (PDLP 1a) confirming that GBNV NSm localizes to PD. Unlike in other movement proteins, the C-terminal coiled coil domain of GBNV NSm was shown to be involved in the localization of NSm to PD, as deletion of this domain resulted in the cytoplasmic localization of NSm. Treatment with Brefeldin A demonstrated the role of ER in targeting GFP NSm to PD. Furthermore, mCherry:NSm co-localized with ER-GFP (endoplasmic reticulum targeting peptide (HDEL peptide fused with GFP). Co-expression of NSm with ER-GFP showed that the ER-network was transformed into vesicles indicating that NSm interacts with ER and remodels it. Mutations in the conserved hydrophobic region of NSm (residues 130-138) did not abolish the formation of vesicles. Additionally, the conserved prolines at positions 140 and 142 were found to be essential for targeting the vesicles to the cell membrane. Further, systematic deletion of amino acid residues from N- and C-terminus demonstrated that N-terminal 203 amino acids are dispensable for the vesicle formation. On the other hand, the C-terminal coiled coil domain when expressed alone could also form vesicles. These results suggest that GBNV NSm remodels the ER network by forming vesicles via its interaction through the C-terminal coiled coil domain. Interestingly, NSm interacts with NP in vitro and coexpression of these two proteins in planta resulted in the relocalization of NP to PD and this relocalization was abolished when the N-terminal unfolded region of NSm was deleted. Thus, the NSm interacts with NP via its N-terminal unfolded region and the NSm-NP complex could in turn interact with the ER membrane via the C-terminal coiled coil domain of NSm to form vesicles that are targeted to PD and there by assist the cell to cell movement of the viral genome complex.

No abstract

The electronic structure, magnetic properties and ferromagnetic transition temperature (Tc) of Vandium (V) doped monolayer (ML) and bilayer (BL) MoS2 are investigated using density function theory (DFT) plus on-site Hubbard potential correction (U). The results show that substitution of V dopant atom at the Mo sites are energetically favorable and magnetic interaction between two dopants in ML and BL MoS2 oscillates from ferromagnetic (FM) to antiferromagnetic (AF) depending on atomic distance between dopants. Our result also shows that a pair of V dopants in different layers of BL MoS2 interacts antiferromagnetically. Moreover, it is obtained that interlayer interaction in BL MoS2 affects the magnetic interaction in V-doped BL MoS2. The calculated ferromagnetic transition temperatures (Tc) value for impurity concentration of 12.5% and 22.22% are 242 and 285 K, respectively, for ML phase. However, for BL phase T[Formula: see text] values are 187 and 256 K for concentration of 6.25% and 11.11%, respectively, these values are closer to room-temperature. Our calculations indicate that, V-doped ML and BL MoS2 are promising candidates for 2D dilute magnetic semiconductors for spintronics applications.

The effect of interlayer interaction on transition temperature (T c ) with number of layers (n) has been investigated in layered high T c superconductors within the BCS theory, irrespective of the pairing mechanism. The expression for interlayer correlation (γ) has been obtained and its implications have been studied. T c has been calculated numerically for n = 1, 2 and 3. Interlayer interactions have been found crucial for superconductivity and enhancing T c . It is also found that mere addition of layers does not increase T c , but the density of states (N 0 ) should also increase with addition of layers. The results are in general agreement with experiments and explain the trend of T c with n satisfactorily. IntroductionThe discovery of high T c cuprates [1] raised the question whether BCS theory continues to be applicable with exceptionally strong coupling or a completely new framework must be developed [2][3][4][5]. As the question of mechanism of superconductivity remains unsettled, many new ideas and proposals have been generated for a possible new mechanism but little consensus has been reached so far. However, the class of high T c superconductors provides useful information, which could give insight into the unconventional nature of superconductivity in these systems.It is now well recognized that all high T c cuprates are based on structures with square planar copper oxide layers [6]. The superconducting phase occurs near a metal insulator transition with the destruction of long-range antiferromagnetic order of Cu spins [7]. These CuO 2 layers are found to be responsible for conduction and increase in their number per unit cell increases T c , being maximum for n = 3 [8,9], and then decreases. They are considered key to the understanding of Physics in these compounds and must be incorporated in any final high T c theory.Beside high T c cuprates, recent years witnessed discovery of many layered superconductors. Fullerides, borocarbides, ruthenates, MgB 2 , intercalated Na x CaO 2 , Ba 1-x K x BiO 3 [10-12] to name a few. The layered structure seems to support high T c and can be a favorable hunting ground for obtaining higher bounds of T c .Several workers [13][14][15][16][17][18][19][20] have studied the role of layered structure on the unusual properties of these compounds and proposed interlayer interactions to play significant role in the enhancement of T c and stabilizing superconducting order with respect to fluctuations. This coupled with the fact that increase in number of layers (for high T c cuprates), increases T c , is a clear indication that layered structure is crucial to high T c superconductors and plays dominant role in establishing superconducting order. Further it is also known that long-range order is impossible in 1D and 2D systems with an order parameter that has a continuous symmetry [22]. Therefore to obtain a real phase transition with long-range order and a homogenous order parameter, one needs to take into account the interlayer coupling. Recently quantum tunneling of cooper ...