Induced Systemic Resistance


Plants have well developed resistance system, which they adapt to cope-up the various abiotic as well biotic stress. They de-novo synthesize certain chemicals to kill the pathogens at the site of attack (local response) or to defend the un-affected parts of the plant far away from the site of infection (systemic response). Systemic Acquired Resistance (SAR) and Induced Systemic Resistance (ISR) are the two systemic defence responses well-studied in plants.


ISR was discovered around 1991, when several researches were carried-out to show that, non-pathogenic bacterial colonization promoted health of plants upon stimulation of their defence response.

Role of PGPR in ISR

Certain rhizospheric mutualistic microbes trigger the ISR in the plants in advance against pathogenic infection or herbivores. Plant growth-promoting rhizobacteria (PGPR) are among such microbes, which have been well utilized in managing the soil and plant health. PGPR may act as a biocontrol agent as these produce inhibitory allelochemicals, thus induce ISR in plant against a broad spectrum of pathogens. Pseudomonas fluorescens, Paenibacillus polymyxa, Piriformospora indica or Trichoderma spp. are among those mutualistic microbes, which are well known for inducing the ISR in associated plants. Microbes mediated ISR sensitizes the pants for faster and stronger defense response, and prepare them to resists against pathogens.


When a pathogen attacks the host plant, either it may establish infection (susceptibility) or plant resist the successful infection (resistance). In the later, the pathogen elicits a cascade of responses, which may be local or systemic. Pathogenic infection results in oxidative burst in the host cells at the side of attack, thus trap the pathogenic propagule locally. In response to the pathogenic attack, plant changes the composition of cell wall making it a physical barrier in order to the resist penetration. In other way, plants de-novo synthesize certain antimicrobial compounds, e.g., phytoalexins and pathogenicity-related proteins (PR proteins), which kill the pathogen. Phytoalexins act locally, whereas, the PR proteins act locally as well systemically.

PR proteins are reported from a number of plants, where they are found in small quantity, but reported to be accumulated in the higher concentration after pathogenic infection. PR proteins are largely divided into two groups. One group of PR is acidic and are found in the intercellular spaces, whereas, other group is basic and found intracellularly in the vacuole. PR proteins are used as ISR markers in pants. PR proteins have chitinase or β‐1,3‐glucanase activity, which hydrolyze chitin of fungal cell wall and provide the resistance to the pants against chitin-containing fungal pathogens. In plants, PR proteins synthesis is surged by both the pathogenic attack as well as on wounding, thus contribute to the ISR. In response to the pathogenic infection, plants de-novo synthesize the SA, whereas, in response to the wounding, plants synthesize jasmonic acid (JA). Whereas JA plays a central role in SAR, the signal in ISR is triggered by SA and ethylene (ET). The PR may or may not be involved in signaling of ISR.

ISR signaling in plants

Microbes mediated ISR shows redundancy in their elicitors. The plant mutant to one elicitor induces the systemic response via another elicitor. ISR is triggered by the rhizospheric microbes via pathway, which involves the JA/ET and redox-regulated protein NON-EXPRESSOR OF PR GENES1 (NPR1), which intern regulate the expression of PR gene.


  • Heil, M. and BOSTOCK, R.M., 2002. Induced systemic resistance (ISR) against pathogens in the context of induced plant defences. Annals of botany, 89(5), pp.503-512.
  • Choudhary, D.K., Prakash, A. and Johri, B.N., 2007. Induced systemic resistance (ISR) in plants: mechanism of action. Indian Journal of Microbiology, 47(4), pp.289-297.
  • Annapurna, K., Kumar, A., Kumar, L.V., Govindasamy, V., Bose, P. and Ramadoss, D., 2013. PGPR-induced systemic resistance (ISR) in plant disease management. In Bacteria in Agrobiology: Disease Management (pp. 405-425). Springer, Berlin, Heidelberg.
  • Romera, F.J., García, M.J., Lucena, C., Martínez-Medina, A., Aparicio, M.A., Ramos, J., Alcántara, E., Angulo, M. and Pérez-Vicente, R., 2019. Induced systemic resistance (ISR) and Fe deficiency responses in dicot plants. Frontiers in Plant Science, 10, p.287.
  • Poveda, J., Hermosa, R., Monte, E. and Nicolás, C., 2019. Trichoderma harzianum favours the access of arbuscular mycorrhizal fungi to non-host Brassicaceae roots and increases plant productivity. Scientific reports, 9(1), pp.1-11.

See also

Content first created on 16-10-2020
last updated on 24-04-2021