Activation Of Induced Resistance Research Articles

Unveiling the structural properties and induced resistance activity in rice of Chitin/Chitosan-Glucan Complex of Rhizoctonia solani AG1 IA inner cell wall

Phytopathogen cell wall polysaccharides have important physiological functions. In this study, we isolated and characterized the alkali-insoluble residue on the inner layers of the Rhizoctonia solani AG1 IA cell wall (RsCW-AIR). Through chemical composition and structural analysis, RsCW-AIR was mainly identified as a complex of chitin/chitosan and glucan (ChCsGC), with glucose and glucosamine were present in a molar ratio of 2.7:1.0. The predominant glycosidic bond linkage of glucan in ChCsGC was β-1,3-linked Glcp, both the α and β-polymorphic forms of chitin were presented in it by IR, XRD, and solid-state NMR, and the ChCsGC exhibited a degree of deacetylation measuring 67.08 %. RsCW-AIR pretreatment effectively reduced the incidence of rice sheath blight, and its induced resistance activity in rice was evaluated, such as inducing a reactive oxygen species (ROS) burst, leading to the accumulation of salicylic acid (SA) and the up-regulation of SA-related gene expression. The recognition of RsCW-AIR in rice is partially dependent on CERK1.

1-Methyltryptophan Treatment Increases Defense-Related Proteins in the Apoplast of Tomato Plants.

The activation of induced resistance in plants may enhance the production of defensive proteins to avoid the invasion of pathogens. In this way, the composition of the apoplastic fluid could represent an important layer of defense that plants can modify to avoid the attack. In this study, we performed a proteomic study of the apoplastic fluid from plants treated with the resistance inducer 1-methyltryptophan (1-MT) as well as infected with Pseudomonas syringae pv. tomato (Pst). Our results showed that both the inoculation with Pst and the application of the inducer provoke changes in the proteomic composition in the apoplast enhancing the accumulation of proteins involved in plant defense. Finally, one of the identified proteins that are overaccumulated upon the treatment have been expressed in Escherichia coli and purified in order to test their antimicrobial effect. The result showed that the tested protein is able to reduce the growth of Pst in vitro. Taken together, in this work, we described the proteomic changes in the apoplast induced by the treatment and by the inoculation, as well as demonstrated that the proteins identified have a role in the plant protection.

Paraburkholderia phytofirmans PsJN Protects Arabidopsis thaliana Against a Virulent Strain of Pseudomonas syringae Through the Activation of Induced Resistance

Paraburkholderia phytofirmans PsJN is a plant growth-promoting rhizobacterium (PGPR) that stimulates plant growth and improves tolerance to abiotic stresses. This study analyzed whether strain PsJN can reduce plant disease severity and proliferation of the virulent strain Pseudomonas syringae pv. tomato DC3000, in Arabidopsis plants, through the activation of induced resistance. Arabidopsis plants previously exposed to strain PsJN showed a reduction in disease severity and pathogen proliferation in leaves compared with noninoculated, infected plants. The plant defense-related genes WRKY54, PR1, ERF1, and PDF1.2 demonstrated increased and more rapid expression in strain PsJN-treated plants compared with noninoculated, infected plants. Transcriptional analyses and functional analysis using signaling mutant plants suggested that resistance to infection by DC3000 in plants treated with strain PsJN involves salicylic acid-, jasmonate-, and ethylene-signaling pathways to activate defense genes. Additionally, activation occurs through a specific PGPR-host recognition, being a necessary metabolically active state of the bacterium to trigger the resistance in Arabidopsis, with a strain PsJN-associated molecular pattern only partially involved in the resistance response. This study provides the first report on the mechanism used by the PGPR P. phytofirmans PsJN to protect A. thaliana against a widespread virulent pathogenic bacterium.

Integrated control of rice kernel smut disease using plant extracts and salicylic acid

The effects of salicylic acid (SA) at three concentrations i.e. 2.5, 5 and 7 mM and plant extracts from pick tooth (Ammi visnaga), liquorice (Glycyrrhiza glabra), artemisia (Artemisia judaica), mint (Mentha viridis), clove (Syzygium aromaticum) and blue gum (Eucalyptus globulus) on the infection of rice kernel smut disease caused by Tilletia barclayana were studied. Spraying of rice plants with different concentrations of SA at seven days before infection was the most effective treatment against pathogen infection. Among all plant extract treatments, M. viridis and S. aromaticum were the most effective treatments. Additionally, our results showed increased levels of peroxidase, polyphenol oxidase, phenylalanine ammonia lyase and chitinase as well as total protein contents in the treated plants compared with the control. In conclusion, accumulations of these oxidative enzymes in plants treated with SA and plant extracts provide their role in the activation of induced resistance against T. barclayana.

Evaluation of chitosan as an inhibitor of soil-borne pathogens and as an elicitor of defence markers and resistance in tobacco plants

In in vitro assays, a chitosan polymer caused differential growth inhibition of the following pathogens isolated from tobacco: Phytophthora parasitica Dastur var. nicotianae (Ppn), Pythium aphanidermatum (Edson) Fitzp, Rhizoctonia solani Kühn, and Sclerotium rolfsii Sacc. The most sensitive were P. aphanidermatum and S. rolfsii, the growth of which was fully inhibited at a chitosan dose of 1.5 g/L; the growth of Ppn was fully inhibited at 2 g/L. In vivo assays involving plants grown from seeds immersed in chitosan, as well as plants sprayed with this product, were performed to detect the induction of defence response markers in the leaf and consequent resistance to disease. Although defence/resistance marker enzyme activities varied, activation was greater in the chitosan-treated plants than in controls. Marker enzyme activities in the sprayed plants were generally equal to or stronger than those recorded in the seed immersion-treated plants, except for phenylalanine ammonia-lyase activity at the lowest immersion concentration tested. Although there were no statistical differences among treatments with respect to resistance against Ppn, the greatest protection was afforded by the spray treatments, in which the infection index was reduced between 17 and 19% compared to the controls. In conclusion, this chitosan polymer directly inhibited the growth of several tobacco pathogens and caused the induction of defence enzymes in leaves, but was not able to protect tobacco plantlets against Ppn infection via the activation of induced resistance. This work demonstrated the potential of chitosan in protecting tobacco plants against soil-borne pathogens.