The LeEIX Locus Determines Pathogen Resistance in Tomato.

The mechanisms underlying the ability of plants to differentiate between pathogens and commensals in their environment are currently unresolved. It has been suggested that spatiotemporal regulation of pattern-recognition receptor (PRR) content could be one of the components providing plants with the ability to distinguish between pathogens and nonpathogenic microbes. The LeEIX PRRs recognize xylanases derived from beneficial or commensal plant colonizers of Trichoderma species, including the xylanase known as EIX. Here, we investigated possible general roles of PRRs from the LeEIX locus in immunity and pathogen resistance in tomato. Mutating the inhibitory PRR LeEIX1, or overexpressing the activating PRR LeEIX2, resulted in resistance to a wide range of pathogens and increased basal and elicited immunity. LeEIX1 knockout caused increases in the expression level of several tested PRRs, including FLS2, as well as bacterial pathogen resistance coupled with an increase in flg22-mediated immunity. The wild tomato relative Solanum pennellii contains inactive LeEIX PRR variants. S. pennellii does not respond to elicitation with the LeEIX PRR ligand EIX. Given that EIX is derived from a mostly nonpathogenic microbe, the connection of its PRRs to disease resistance has not previously been investigated directly. Here, we observed that compared with S. lycopersicum cultivar M82, S. pennellii was more sensitive to several fungal and bacterial pathogens. Our results suggest that the LeEIX locus might determine resistance to fungal necrotrophs, whereas the resistance to biotrophs is effected in combination with a gene/quantitative trait locus not within the LeEIX locus.

Anti-biofilm and anti-virulence potential of 3,7-dimethyloct-6-enal derived from Citrus hystrix against bacterial blight of rice caused by Xanthomonas oryzae pv. oryzae.

The present investigation for the first time explains the anti biofilm and anti virulence potential of Kaffir lime oil (KLO) and its major constituent, Citronellal (3,7-dimethyloct-6-enal) against Xanthomonas oryzae pv. oryzae, causal organism of bacterial blight disease of rice. KLO at 500 ppm showed potential activity against X. oryzae pv. oryzae. Among the major components identified, citronellal (CIT) at 75 µM concentration was found to significantly inhibit biofilm along with the swimming and swarming potential of X. oryzae pv. oryzae. In contrary, CIT did not affect the metabolic status and growth kinetics of the bacterial cells. Gene expression analysis showed down regulation in motA, cheD, cheY, flgF, gumC, xylanase, endogluconase, cellulose, cellobiosidase, virulence and rpfF transcript levels by citronellal treatment. However, an insignificant effect of 75 µM CIT treatment was observed on motB, flgE, pilA, estY, pglA, protease and lytic genes expression. Finally, the observations recorded were in confirmity with the virulence leaf clip test as lesion length was significantly decreased (39%) in CIT treatment as compared to the control leaves inoculated with only X. oryzae pv. oryzae. Overall, the findings obtained advocate the use of CIT for promising anti biofilm and anti virulence activity which in turn can be used for managing the blight disease in rice.

Microbial interference mitigates Meloidogyne incognita mediated oxidative stress and augments bacoside content in Bacopa monnieri L.

Microbial interference plays an imperative role in plant development and response to various stresses. However, its involvement in mitigation of oxidative stress generated by plant parasitic nematode in plants remains elusive. In the present investigation, the efficacy of microbe's viz., Chitiniphilus sp. MTN22 and Streptomyces sp. MTN14 single and in combinations was examined to mitigate oxidative stress generated by M. incognita in medicinal plant, Bacopa monnieri. Microbial combination with and without pathogen also enhanced the growth parameters along with secondary metabolites (bacoside) of B. monnieri than the pathogen inoculated control. The study showed that initially the production of hydrogen peroxide (H2O2) was higher in dual microbes infected with pathogen which further declined over M. incognita inoculated control plants. Superoxide dismutase and free radical scavenging activity were also highest in the same treatment which was linearly related with least lipid peroxidation and root gall formation in B. monnieri under the biotic stress. Microscopic visualization of total reactive oxygen species (ROS), H2O2, superoxide radical and programmed cell death in host plant further extended our knowledge and corroborated well with the above findings. Furthermore, scanning electron microscopy confirmed good microbial colonization on the host root surface around nematode penetration sites in plants treated with dual microbes under pathogenic stress. The findings offer novel insight into the mechanism adopted by the synergistic microbial strains in mitigating oxidative stress and simultaneously stimulating bacoside production under pathogenic stress.

Microbe-based technology ameliorates glandular trichomes, secondary metabolites and antioxidants in Pelargonium graveolens L'Hér.

BACKGROUND: Despite the vast exploration of microbes for plant health, there is a lack of knowledge about the synergistic effects of specific microorganisms in sustainable agriculture, especially in medicinal plants such as Pelargonium graveolens L'Hér. The aim of this study was to evaluate how synergistic microbes Trichoderma harzianum ThU, Glomus intraradices and Bacillus subtilis CIM affected crop productivity, secondary metabolites and glandular trichome number in P. graveolens. RESULTS: The results demonstrated a significant (P < 0.05) increase in plant growth, secondary metabolites, total chlorophyll, carotenoids, carbohydrates, total phenolics, total flavonoids, free radical-scavenging activity and total antioxidant capacity of P. graveolens treated with synergistic bioinoculants as compared with the control. Most interestingly, an increase in essential oil by 32% in the treatment with all three microbes was observed. Furthermore, the principal aroma compounds citronellol and geraniol also increased in the same treatment. A positive and direct correlation was observed between essential oil content and number of glandular trichomes in all treatments. CONCLUSION: The present study highlights an explicit amalgamation of prospective microbes showing potential for synergism that act as biostimulants in enhancing plant production and improving the antioxidant and aroma profile of P. graveolens. © 2016 Society of Chemical Industry.

Exploitation of microbes for enhancing bacoside content and reduction of Meloidogyne incognita infestation in Bacopa monnieri L.

Despite the vast exploration of rhizospheric microbial wealth for crop yield enhancement, knowledge about the efficacy of microbial agents as biocontrol weapons against root-knot disease is scarce, especially in medicinal plants, viz., Bacopa monnieri. In the present investigation, rhizospheric microbes, viz., Bacillus megaterium, Glomus intraradices, Trichoderma harzianum ThU, and their combinations were evaluated for the management of Meloidogyne incognita (Kofoid and White) Chitwood and bacoside content enhancement in B. monnieri var CIM-Jagriti. A novel validated method Fourier transform near infrared was used for rapid estimation of total bacoside content. A significant reduction (2.75-fold) in root-knot indices was observed in the combined treatment of B. megaterium and T. harzianum ThU in comparison to untreated control plants. The same treatment also showed significant enhancement (1.40-fold) in total bacoside contents (plant active molecule) content using Fourier transform near-infrared (FT-NIR) method that analyses samples rapidly in an hour without solvent usage and provides ample scope for natural product studies.