Mycorrhiza-Induced Resistance and Priming of Plant Defenses

Abstract

Symbioses between plants and beneficial soil microorganisms like arbuscular-mycorrhizal fungi (AMF) are known to promote plant growth and help plants to cope with biotic and abiotic stresses. Profound physiological changes take place in the host plant upon root colonization by AMF affecting the interactions with a wide range of organisms below- and above-ground. Protective effects of the symbiosis against pathogens, pests, and parasitic plants have been described for many plant species, including agriculturally important crop varieties. Besides mechanisms such as improved plant nutrition and competition, experimental evidence supports a major role of plant defenses in the observed protection. During mycorrhiza establishment, modulation of plant defense responses occurs thus achieving a functional symbiosis. As a consequence of this modulation, a mild, but effective activation of the plant immune responses seems to occur, not only locally but also systemically. This activation leads to a primed state of the plant that allows a more efficient activation of defense mechanisms in response to attack by potential enemies. Here, we give an overview of the impact on interactions between mycorrhizal plants and pathogens, herbivores, and parasitic plants, and we summarize the current knowledge of the underlying mechanisms. We focus on the priming of jasmonate-regulated plant defense mechanisms that play a central role in the induction of resistance by arbuscular mycorrhizas.

Organically Grown Soybean Production in the USA: Constraints and Management of Pathogens and Insect Pests

“…This will stimulate germination and hyphal growth, resulting in the formation of a symbiotic connection with roots of the plant host. The extra radical hyphae will extend past the root system to obtain immobile nutrients, particularly phosphorus, in exchange for carbon from the plant [50,51].…”

“…Their positive impact on crop production includes suppression of certain diseases by outcompeting pathogens for root tissue and stimulating host defense responses. To establish a symbiotic relationship, AM fungi interact with the plant to alter some specific plant defense pathways including the salicylic acid-dependent and the jasmonic acid/ethylene-dependent pathways to establish successful associations with roots [51]. The altering of these defense pathways often makes mycorrhizal plants more resistant to necrotrophic pathogens and chewing insects, but may make the plants more susceptible to biotrophic pathogens [51].…”

“…To establish a symbiotic relationship, AM fungi interact with the plant to alter some specific plant defense pathways including the salicylic acid-dependent and the jasmonic acid/ethylene-dependent pathways to establish successful associations with roots [51]. The altering of these defense pathways often makes mycorrhizal plants more resistant to necrotrophic pathogens and chewing insects, but may make the plants more susceptible to biotrophic pathogens [51]. Mycorrhizal induced resistance has been shown to reduce disease severity in roots and also in shoots of colonized plants [51].…”

“…The altering of these defense pathways often makes mycorrhizal plants more resistant to necrotrophic pathogens and chewing insects, but may make the plants more susceptible to biotrophic pathogens [51]. Mycorrhizal induced resistance has been shown to reduce disease severity in roots and also in shoots of colonized plants [51]. However, the effect of AM fungi is highly dependent on the host-pathogen-AM fungi interaction.…”

Properties of the halophyte microbiome and their implications for plant salt tolerance

“…A screen of 17 phyllosphere endophytes isolated from the Karangkadu mangrove ecosystem in India identified eight strains with a broad spectrum of antibacterial activity (Sundaram et al 2011a(Sundaram et al , 2011b. Induction of resistance against pathogens has been also described for the interaction of plant roots with mycorrhizal fungi (Jung et al 2012), with dark septate endophytes (Andrade-Linares et al 2011) and with the endophyte Piriformospora indica (Waller et al 2005). Although a large body of data was generated for the trilateral relationship between pathogens, growth-promoting microbes, and glycophytes, respective investigations concerning interactions with halophytes are scarce (Fig.…”