Argonaute 8 (AGO8) Mediates the Elicitation of Direct Defenses against Herbivory.

In Nicotiana attenuata, specific RNA-directed RNA polymerase (RdR1) and the Dicer-like (DCL3 and DCL4) proteins are recruited during herbivore attack to mediate the regulation of defense responses. However, the identity and role(s) of Argonautes (AGOs) involved in herbivory remain unknown. Of the 11 AGOs in the N. attenuata genome, we silenced the expression of 10. Plants silenced in NaAGO8 expression grew normally but were highly susceptible to herbivore attack. Larvae of Manduca sexta grew faster when consuming inverted-repeat stable transformants (irAGO8) plants but did not differ from the wild type when consuming plants silenced in AGO1 (a, b, and c), AGO2, AGO4 (a and b), AGO7, or AGO10 expression. irAGO8 plants were significantly compromised in herbivore-induced levels of defense metabolites such as nicotine, phenolamides, and diterpenoid glycosides. Time-course analyses revealed extensively altered microRNA profiles and the reduced accumulation of MYB8 transcripts and of the associated genes of the phenolamide and phenylpropanoid pathways as well as the nicotine biosynthetic pathway. A possible AGO8-modulated microRNA-messenger RNA target network was inferred. Furthermore, comparative analysis of domains revealed the diversity of AGO conformations, particularly in the small RNA-binding pocket, which may influence substrate recognition/binding and functional specificity. We infer that AGO8 plays a central role in the induction of direct defenses by modulating several regulatory nodes in the defense signaling network during herbivore response. Thus, our study identifies the effector AGO of the herbivore-induced small RNA machinery, which in N. attenuata now comprises RdR1, DCL3/4, and AGO8.

Analysis of copper tolerant rhizobacteria from the industrial belt of Gujarat, western India for plant growth promotion in metal polluted agriculture soils.

Agricultural sites irrigated for long term with water polluted by industrial effluents containing heavy metals might adversely affect the soil microbial communities and crop yield. Hence it is important to study rhizobacterial communities and their metal tolerance in such affected agricultural fields to restore soil fertility and ecosystem. Present work deals with the study of rhizobacterial communities from plants grown in copper (Cu) contaminated agricultural fields along the industrial zone of Gujarat, India and are compared with communities from a Cu mine site. Microbial communities from rhizosphere soil samples varied in the magnitude of their Cu tolerance index indicating differences in long term pollution effects. Culture dependent denaturing gradient gel electrophoresis (CD-DGGE) of bacterial communities revealed the diverse composition at the sampling sites and a reduced total diversity due to Cu toxicity. Analysis of 16S rRNA gene diversity of Cu tolerant rhizobacteria revealed the predominance of Enterobacter spp. and Pseudomonas spp. under Cu stress conditions. Cu tolerant bacterial isolates that were able to promote growth of mung bean plants in vitro under Cu stress were obtained from these samples. Cu tolerant rhizobacterium P36 identified as Enterobacter sp. exhibited multiple plant growth promoting traits and significantly alleviated Cu toxicity to mung bean plants by reducing the accumulation of Cu in plant roots and promoted the plant growth in CuSO4 amended soils.

Copper-induced modifications in early symbiotic signaling factors of Ensifer (Sinorhizobium)-Medicago interactions.

Cu is an essential micronutrient required during nitrogen fixation, but above threshold concentrations it becomes toxic. The present study was aimed at studying the effect of high Cu concentrations on the early plant-microbe interactions between Ensifer (Sinorhizobium) meliloti 1021, a symbiotic diazotrophic bacterium belonging to α-Proteobacteria, and its plant host Medicago truncatula. E. meliloti exhibited pleomorphism with elongated and branched growth at 100 µM Cu which brought about 50 % reduction in growth. Early symbiotic signaling factors like exopolysaccharides and lipopolysaccharides levels and biofilm formation were adversely affected at sublethal levels of Cu. Cu stress resulted in over-expression of proteins such as GroEL (60 kDa chaperonin) and WrbA (NAD(P)H dehydrogenase). E. meliloti was unable to show efficient attachment on the roots of M. truncatula at 3 µM Cu, which corresponds to 50 % growth inhibitory levels for the plant, indicating that plant root surface modifications may also contribute to adverse effect of Cu on early plant-microbe interactions during nodulation.

Elucidation of defense-related signaling responses to spot blotch infection in bread wheat (Triticum aestivum L.).

Spot blotch disease, caused by Bipolaris sorokiniana, is an important threat to wheat, causing an annual loss of ~17%. Under epidemic conditions, these losses may be 100%, yet the molecular responses of wheat to spot blotch remain almost uncharacterized. Moreover, defense-related phytohormone signaling genes have been poorly characterized in wheat. Here, we have identified 18 central components of salicylic acid (SA), jasmonic acid (JA), ethylene (ET), and enhanced disease susceptibility 1 (EDS1) signaling pathways as well as the genes of the phenylpropanoid pathway in wheat. In time-course experiments, we characterized the reprogramming of expression of these pathways in two contrasting genotypes: Yangmai #6 (resistant to spot blotch) and Sonalika (susceptible to spot blotch). We further evaluated the performance of a population of recombinant inbred lines (RILs) by crossing Yangmai#6 and Sonalika (parents) and subsequent selfing to F10 under field conditions in trials at multiple locations. We characterized the reprogramming of defense-related signaling in these RILs as a consequence of spot blotch attack. During resistance to spot blotch attack, wheat strongly elicits SA signaling (SA biogenesis as well as the NPR1-dependent signaling pathway), along with WRKY33 transcription factor, followed by an enhanced expression of phenylpropanoid pathway genes. These may lead to accumulation of phenolics-based defense metabolites that may render resistance against spot blotch. JA signaling may synergistically contribute to the resistance. Failure to elicit SA (and possibly JA) signaling may lead to susceptibility against spot blotch infection in wheat.

Assessment of microbial communities in mung bean (Vigna radiata) rhizosphere upon exposure to phytotoxic levels of Copper.

Pollution of agricultural soils by Cu is of concern as it could bring about alterations in microbial communities, ultimately eliminating certain plant beneficial bacteria thus disturbing soil fertility and plant growth. To understand the response of rhizobacterial communities upon Cu perturbation, mung bean (Vigna radiata) plants were grown in agricultural soil amended with CuSO4 (0-1000 mg kg(-1) ) under laboratory conditions. Culture-independent and -dependent Denaturing Gradient Gel Electrophoresis (CI-DGGE and CD-DGGE) fingerprinting techniques were employed to monitor rhizobacterial community shifts upon Cu amendment. In group specific PCR-DGGE, a negative impact was seen on α-Proteobacteria followed by ß-Proteobacteria resulting in a concomitant decrease in diversity indices with increased Cu concentration. No significant changes were observed in Firmicutes and Actinomycetes populations. In CD-DGGE rhizobacterial community shift was observed above 500 mg kg(-1) (CuSO4 ), however certain bands were predominantly present in all treatments. Plants showed toxic effects by reduction in growth and elevated Cu accumulation, with root system being affected prominently. From this study it is evident that above 250 mg kg(-1) , rhizobacterial communities are adversely affected. α-Proteobacteria was found to be a sensitive bio-indicator for Cu toxicity and is of particular significance since this group includes majority of plant growth promoting rhizobacteria.

Detection of Enterococcus faecalis and Candida albicans in previously root-filled teeth in a population of Gujarat with polymerase chain reaction.

BACKGROUND: Micro-organisms are the primary causative agents of endodontic infections. Phenotype based procedures for bacterial identification has certain drawbacks especially, when investigating the microbiota of root-filled teeth. Thus, more sensitive methods like Polymerase chain reaction (PCR) can provide results that are more accurate and reliable for the microbial prevalence in the root filled teeth. AIM: In this study, we have investigated twenty symptomatic root-filled teeth with chronic apical periodontitis for the prevalence of Enterococcus faecalis and Candida albicans in the root filled teeth associated with symptomatic cases with or without periradicular lesions. MATERIALS AND METHODS: Microbiological samples were taken from the canals immediately after removal of previous gutta percha cones using aseptic techniques. After removal of root canal filling, samples were obtained with paper points placed in the canal. Paper points were transferred to a cryotube containing "Tris EDTA" buffer and immediately frozen at -20°C. RESULTS: By PCR amplification of the samples using taxon specific primers, E. faecalis was found to be prevalent species, detected in 65% of the cases and C. albicans was detected in 35% of cases. CONCLUSION: The results of the study shows that geographical influence and dietary factors might have some role to play in the prevalence of the species like C. albicans and presence of E. faecalis confirming the assertion of previous culture-dependent and independent approaches for the microbiological survey of root filled teeth.