Figure Legend: Solid lines represent hormone mediated up-regulation (arrow) or inhibition (blunt-end line). Dotted lines represent pathogen identification by the host. Dashed lines represent some transcription factors or processes involved in hormone crosstalk. The different phytohormones are indicated by various colors. Dark blue shapes with white font represent transcription factors or processes that are activated in the nucleus. CW = cell wall and PM = plasma membrane.
How do plants recognize to pathogen attack?
Plants recognize and respond to pathogens via two major defense mechanisms. The most basal defense response is referred to as PAMP-Triggered Immunity, or PTI. When some pathogens evolved to overcome PTI, they began to secrete effector proteins to evade PTI and cause disease. In response to more successful pathogens that evolved to use effectors, plants can defend themselves through Effector-Triggered Immunity, or ETI. Each of these responses, PTI and ETI, allows for the plants to recognize pathogen attack and deploy an appropriate defense response.
How do plant hormones assist in the deployment of an appropriate immune response?
Plant hormones tend to act interdependently with one another through complex antagonistic (negative) or synergistic (positive) interactions, referred to as hormone crosstalk.
Why is hormone crosstalk important in relation to immunity?
Hormone crosstalk is important because these interactions result in changes in plant physiology that allow for the plant to appropriately defend itself against pathogen attack. Although, in the case of successful pathogens, hormone crosstalk can result in physiological changes that increase host susceptibility allowing for more pathogenic growth throughout the plant.
How does each plant hormone contribute to immune response?
Firstly, no single plant hormone in plants is responsible for activating all immune responses to pathogens. Instead all plant hormones interact in a complex, interconnected interactions as a means to mediate plant immunity and this is referred to as hormonal cross-talk. The figure below is a conceptualized over-view of how each plant hormone contributes to plant immunity. In general, in response to biotrophic pathogens salicylic acid (SA) is up-regulated, whereas in response to neurotrophic pathogens, jasmonic acid (JA) and ethylene (ET) are up-regulated. To fine-tune the host immune response other abiotic stress and growth hormones contribute to immunity such as: abscisic acid (ABA), cytokinin (CK), auxin (AUX), gibberellin acid (GA), and brassinosteroid (BR). These hormones typically contribute to host immunity through up-regulation or down-regulation of either the SA or JA/ET branches.
Shigenaga & Argueso, 2016
PLANT HORMONES IN IMMUNITY
