Antiviral Silencing and Suppression of Gene Silencing in Plants

RNA silencing is an evolutionary conserved sequence-specific gene inactivation mechanism that contributes to the control of development, maintains heterochromatin, acts in stress responses, DNA repair and defends against invading nucleic acids like transposons and viruses. In plants RNA silencing functions as one of the main immune systems. RNA silencing process involves the small RNAs and trans factor components like Dicers, Argonautes and RNA-dependent RNA poly- merases. To deal with host antiviral silencing responses viruses evolved mecha- nisms to avoid or counteract this, most notably through expression of viral suppressors of RNA silencing. Due to the overlap between endogenous and antiviral silencing pathways while blocking antiviral pathways viruses also impact endogenous silencing processes. Here we provide an overview of antiviral silencing pathway, host factors implicated in it and the crosstalk between antiviral and endogenous branches of silencing. We summarize the current status of knowledge about the viral counter-defense strategies acting at various steps during virus infection in plants with the focus on representative, well studied silencing suppres- sor proteins. Finally we discuss future challenges of the antiviral silencing and counter-defense research field

PGP potential, abiotic stress tolerance and antifungal activity of <i>Azotobacter</i> strains isolated from paddy soils

322-331Azotobacter strains were isolated by serial dilution method and colonies were viscous, smooth, glistening, and brown to black colour on Jenson’s N-free agar. Morphological and biochemical tests showed characteristic features of Azotobacter. Further, molecular analyses revealed the presence of different Azotobacter species viz., <i style="mso-bidi-font-style: normal">A. armeniacus, A. chroococcum, A. salinestris, A. tropicalis and A. vinelandii. The isolates were tested for their ability of nitrogen fixation, indole acetic acid (IAA), gibberllic acid production and phosphate solubilization. Four isolates (GVT-1, GVT-2 KOP-11 and SND-4) were efficient in fixation of highest amount of N2 (29.21 μg NmL-1day-1), produced IAA (25.50 µg mL-1), gibberllic acid (17.25 μg 25 mL-1) and formed larger P solubilizing zone (13.4 mm). Some of the Azotobacter strains were produced siderophores, hydrogen cyanide and were positive for ammonia production with respect to antifungal activity of <i style="mso-bidi-font-style: normal">Azotobacter was tested with dual culture method and A. tropicalis inhibited the growth of Fusarium, Aspergillus and Alternaria species. <i style="mso-bidi-font-style: normal">Azotobacter isolates were tested against salt (0-10%), temperature (4-55ºC), pH (5.0-10) and insecticide chloropyrifos (0-3%) tolerance study. Among them, A. chroococcum was found tolerant to a maximum of 6% NaCl with a temperature of 35-45ºC and to a pH up to 8. All the 4 strains showed effective growth against 3% chloropyrifos concentration. The studies revealed that the Azotobacter strains not only produced plant growth promoting substances but are also tolerant to abiotic stresses such as temperature, pH and insecticides.</span

Potato spindle tuber viroid infection triggers degradation of chloride channel protein CLC-b-like and Ribosomal protein S3a-like mRNAs in tomato plants

Abstract : It is well established that viroid derived small RNA (vd-sRNA) induces RNA silencing of endogenous mRNA. However, it remains not clear how exactly viroid infections can lead to severe symptom induction given the fact that fewer vd-sRNAs binding the specific target mRNAs were recovered from the infected plants. To answer this question, the two least expressed (+) and (−) strand vd-sRNAs of potato spindle tuber viroid (PSTVd) binding to both the 3′ UTR and the coding region of tomato mRNAs were analyzed by infecting tomato plants with two variants of PSTVd. As products of these putative target mRNAs are involved in plant phenotype, the effect of this viroid on these genes were analyzed by infecting tomato plants with two variants of PSTVd. The direct interaction between the vd-sRNAs and putative mRNAs was validated by artificial microRNA experiments in a transient expression system and by RNA ligase-mediated rapid amplification of cDNA ends. Parallel analysis of RNA ends of viroid infected plants revealed the widespread cleavage of the target mRNAs in locations other than the vd-sRNA binding site during the viroid infection implying the viroid-infection induced vd-sRNA independent degradation of endogenous mRNAs during viroid infection