Salicylic Acid in Plant Symbioses: Beyond Plant Pathogen Interactions

Abstract

Plants form beneficial symbioses with a wide variety of microorganisms. Among these, endophytes, arbuscular mycorrhizal fungi (AMF), and nitrogen-fixing rhizobia are some of the most studied and well understood symbiotic interactions. These symbiotic microorganisms promote plant nutrition and growth. In exchange, they receive the carbon and metabolites necessary for their development and multiplication. In addition to their role in plant growth and development, these microorganisms enhance host plant tolerance to a wide range of environmental stress. Multiple studies have shown that these microorganisms modulate the phytohormone metabolism in the host plant. Among the phytohormones involved in the plant defense response against biotic environment, salicylic acid (SA) plays an important role in activating plant defense. However, in addition to being a major actor in plant defense signaling against pathogens, SA has also been shown to be involved in plant–microbe symbiotic interactions. In this review, we summarize the impact of SA on the symbiotic interactions. In addition, we give an overview of the impact of the endophytes, AMF, and rhizobacteria on SA-mediated defense response against pathogens.

Comparative transcriptome profiling reveals the role of phytohormones and phenylpropanoid pathway in early-stage resistance against powdery mildew in watermelon (Citrullus lanatus L.)

“…Plants have a wide variety of active and passive defense mechanisms at their disposal in the event that they come under attack by pathogens ( Ausubel, 2005 ; Kumar et al., 2021 ; Benjamin et al., 2022 ). Active defense responses, which require de novo protein synthesis, are controlled by a complex and interconnected network of signaling pathways that primarily involve three molecules, ethylene (ET), jasmonic acid (JA) and salicylic acid (SA) and which results in the synthesis of pathogenesis-related (PR) proteins ( Jones and Dangl, 2006 ; Sood et al., 2021 ; Fidler et al., 2022 ).…”

“…All plant defensive responses are the consequence of the interaction of numerous genes and gene families that coordinate in a network ( Pandey and Somssich, 2009 ; Kumar et al., 2021 ). Through the regulation of genes, several phytohormones are recognized to have a significant part in multiple processes ( Figueroa-Macias et al., 2021 ; Zhao et al., 2021 ; Benjamin et al., 2022 ). Furthermore, plants maintain homeostasis and adjust to environmental changes.…”

“…These phytohormones regulate growth, development, and physiological activities in addition to defensive signals. Auxins, cytokinins, gibberellins, ethylene, jasmonic acid, brassinosteroid, salicylic acid, and abscisic acid are phytohormones that respond to stress by acting synergistically and antagonistically in a process known as signaling cross-talk ( Benjamin et al., 2022 ; Fidler et al., 2022 ). These phytohormones cooperate harmoniously and react to environmental and developmental factors.…”

<em>Epichloë</em> Endophytes Shape the Foliar Endophytic Fungal Microbiome and Alter the Auxin and Salicylic Acid Phytohormone Levels in Two Meadow Fescue Cultivars

“…An inducing effect of endophyte symbiosis on salicylic acid concentrations has been connected to a better defense response against biotrophic pathogens and piercing sucking insects [28,55]. On the other hand, SA reduction in symbiotic plants has earlier been reported in Epichloë-symbiotic plants and can be an Epichloë-mediated suppression of the host immune response for a better intercellular establishment [56]. Due to the key role of SA for interactions with biotrophic pathogens, the observed reduction in SA concentrations in endophyte symbiotic plants is likely to be responsible for changes in the endophytic mycosphere [27].…”

Mycorrhizal Association and Plant Disease Protection: New Perspectives

“…However, the molecular mechanisms that regulate the formation and establishment of AM symbiosis and the modulation of plant defense responses during MIR are still not understood [134]. According to Fiorilli et al [135], who elucidate the molecular mechanisms underlying the establishment of AM symbiosis, we need to investigate the changes in transcripts and proteins in roots and leaves during the double (plant-AM fungus) and tripartite (plant-AM fungus-pathogen) interactions [136,137]. The recognition of friend versus foe is still incompletely understood in signaling between the host plant and the pathogen interaction [138][139][140][141].…”