Plants have developed sophisticated molecular mechanisms to detect pathogens and parasites and to activate immune response. Immune response in plants is regulated by phytohormones, that are low molecular weight molecules which interact in a complex network to regulate also many aspects of plant growth, photosynthesis, flowering, reproduction, seed production and response to environmental abiotic challenges. Innate immune system in plants should be considered as within plant growth processes; thus, expressing constitutive defense systems occur only at the cost of plant growth and encounter the risk of allocating resources to defense in the absence of natural pathogens and pests. An effective alternative is to fine-tune immune responses by modulating the "immunological memory" of plants, as it occurs in animals. An aspect of this modulation may be represented by the so-called "priming" by which previously attacked plants respond more quickly or more strongly to a subsequent attack. Such a priming may be realized by Systemic Acquired Resistance (SAR) that is typically induced following effector-triggered immunity (ETI) or, in other words, R gene-mediated resistance, and is effective against a wide range of biotrophic pathogens, and important biotrophic parasites as the soil-borne sedentary endoparasitic cyst and root-knot nematodes. Salicylic acid (SA) is the key regulator of either R gene-mediated resistance to biotrophic pathogens or SAR. Priming is a relatively low-cost mechanism of advancing plant defense, as resources are not used until the threat returns. There is an epigenetic regulation of priming as there is a lack of significant transcriptional changes in primed plants unless they are exposed to the priming agent/hormone. Defense responses in plants primed with a low, non-effective concentration of a defensive hormone are also faster and stronger than those in non-primed plants. Moreover, priming can be trans-generationally transferred to offspring. Another distinct pathway that is associated with induced immune response in plants is based on the plant hormones jasmonic acid (JA) and ethylene (ET) functioning as signaling molecules. JA and ET are involved in an induced systemic resistance (ISR) mediated by beneficial soil organisms such as arbuscular mycorrhiza forming fungi (AMF) and plant growth promoting rhizobacteria (PGPR). JA pathway is primarily induced in ISR which is effective mainly against herbivores and necrotrophic pathogens. Hormone network interactions are as important for plant immune system expression that pathogens and parasites have developed sophisticated molecular mechanisms to deregulate the biosynthesis of hormones and/or to interfere with hormonal signaling pathways thus impairing plant defense response. Moreover, there is in plants a crosstalk between SA and JA signaling pathways that often results in reciprocal antagonism, which may represent a cost-saving measure to properly face by distinct defense strategies phenotypically different attackers. Finally, appropriate treatments of plants with exogenously added salicylic and jasmonic acids, or AMF/PGPR that induce jasmonate signaling system, have been proved to represent a natural stimulation of the immune system of plants to be used against plant parasitic nematodes and herbivore insects, that are pests of paramount importance to horti-crops.
Immune responses induced by salicylic and jasmonic acids against plant parasites
Molinari S
2015
Abstract
Plants have developed sophisticated molecular mechanisms to detect pathogens and parasites and to activate immune response. Immune response in plants is regulated by phytohormones, that are low molecular weight molecules which interact in a complex network to regulate also many aspects of plant growth, photosynthesis, flowering, reproduction, seed production and response to environmental abiotic challenges. Innate immune system in plants should be considered as within plant growth processes; thus, expressing constitutive defense systems occur only at the cost of plant growth and encounter the risk of allocating resources to defense in the absence of natural pathogens and pests. An effective alternative is to fine-tune immune responses by modulating the "immunological memory" of plants, as it occurs in animals. An aspect of this modulation may be represented by the so-called "priming" by which previously attacked plants respond more quickly or more strongly to a subsequent attack. Such a priming may be realized by Systemic Acquired Resistance (SAR) that is typically induced following effector-triggered immunity (ETI) or, in other words, R gene-mediated resistance, and is effective against a wide range of biotrophic pathogens, and important biotrophic parasites as the soil-borne sedentary endoparasitic cyst and root-knot nematodes. Salicylic acid (SA) is the key regulator of either R gene-mediated resistance to biotrophic pathogens or SAR. Priming is a relatively low-cost mechanism of advancing plant defense, as resources are not used until the threat returns. There is an epigenetic regulation of priming as there is a lack of significant transcriptional changes in primed plants unless they are exposed to the priming agent/hormone. Defense responses in plants primed with a low, non-effective concentration of a defensive hormone are also faster and stronger than those in non-primed plants. Moreover, priming can be trans-generationally transferred to offspring. Another distinct pathway that is associated with induced immune response in plants is based on the plant hormones jasmonic acid (JA) and ethylene (ET) functioning as signaling molecules. JA and ET are involved in an induced systemic resistance (ISR) mediated by beneficial soil organisms such as arbuscular mycorrhiza forming fungi (AMF) and plant growth promoting rhizobacteria (PGPR). JA pathway is primarily induced in ISR which is effective mainly against herbivores and necrotrophic pathogens. Hormone network interactions are as important for plant immune system expression that pathogens and parasites have developed sophisticated molecular mechanisms to deregulate the biosynthesis of hormones and/or to interfere with hormonal signaling pathways thus impairing plant defense response. Moreover, there is in plants a crosstalk between SA and JA signaling pathways that often results in reciprocal antagonism, which may represent a cost-saving measure to properly face by distinct defense strategies phenotypically different attackers. Finally, appropriate treatments of plants with exogenously added salicylic and jasmonic acids, or AMF/PGPR that induce jasmonate signaling system, have been proved to represent a natural stimulation of the immune system of plants to be used against plant parasitic nematodes and herbivore insects, that are pests of paramount importance to horti-crops.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
