Plant G-protein signaling cascade and host defense

The heterotrimeric guanine-nucleotide-binding proteins (G-proteins) play a crucial role in signal transduction and regulate plant responses against biotic and abiotic stresses. Necrotrophic pathogens trigger Gα subunit and, in contrast, sometimes Gβγ dimers. Beneficial microbes play a vital role in the activation of heterotrimeric G-proteins in plants against biotrophic and necrotrophic pathogens. The subunits of G-protein (α, β, and γ) are activated differentially against different kinds of pathogens which in turn regulates the entry of the pathogen in a plant cell. Defense mediated by G-proteins in plants imparts resistance against several pathogens. Activation of different G-protein subunits depends on the mode of nutrition of the pathogen. The current review discussed the role of the three subunits against various pathogens. It appeared to be specific in the individual host-pathogen system as well as the role of effectors in the induction of G-proteins. We also discussed the G-protein-mediated production of reactive oxygen species (ROS), including H₂O₂, activation of NADPH oxidases, hypersensitive response (HR), phospholipases, and ion channels in response to microorganisms.

Expression analysis of defense signaling marker genes in Capsicum annuum in response to phytohormones elicitation

BACKGROUND

To tolerate biotic stress, plants employ phytohormones such as jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) to regulate the immune response against different pathogens. Phytohormone-responsive genes, known as "Defense signaling marker genes," are used to evaluate plant disease resistance during pathogen infection. Most information on these marker genes derives from studies on the model plant Arabidopsis thaliana. The present study was aimed analyze the effect of hormonal elicitation at different concentrations at 24 h pos-treatment in the transcript level of 8 traditional genes selected for molecular studies plant-pathogen interactions in Capsicum.

METHODS AND RESULTS

Chemical treatment was achieved by spraying leaves of in vitro seedlings C. annuum L. with 0.1 mM, 1 mM or 2.5 mM ET; 1 mM, 2.5 mM, or 5 mM SA; 2.5 mM BABA; or 0.150 mM MeJA. Twenty-four hours after treatments were applied molecular analyses were carried out using qPCR to investigate the expression. Results revealed that 1 mM of ET or 0.15 mM of MeJA activated the expression CaPR1 (18--11.64-fold change), CaLOX2 (13.80-fold), CaAP2/ERF06 (22- 5.3- fold change), and CaPDF1.2 (2.3-1.5- fold). While, 5 mM of SA present effect of negative regulation on the expression in most of these genes.

CONCLUSIONS

Our results show that the expression profile induced by phytohormones in CaPR1 are particular in C. annuum, because were significantly induced for ET/MeJA, and dow-regulation with SA Contrary to Arabidopsis. Although, on both plants it is observed the cross talk between JA/ET and SA mediated signal pathways for the regulation of this gene.