Systemic acquired resistance
Encyclopedia
The systemic acquired resistance (SAR) is a "whole-plant" resistance response that occurs following an earlier localized exposure to a pathogen
. SAR is analogous to the innate immune system
found in animals, and there is evidence that SAR in plants and innate immunity in animals may be evolutionarily conserved. SAR is important for plants to resist disease, as well as to recover from disease once formed. SAR can be induced by a wide range of pathogens, especially (but not only) those that cause tissue necrosis, and the resistance observed following induction of SAR is effective against a wide range of pathogens, which is why SAR resistance is sometimes called "broad spectrum." SAR is associated with the induction of a wide range of gene
s (so called PR or "pathogenesis-related" genes), and the activation of SAR requires the accumulation of endogenous
salicylic acid
(SA). The pathogen-induced SA signal activates a molecular signal transduction
pathway that is identified by a gene called NIM1, NPR1 or SAI1 (three names for the same gene) in the model genetic system Arabidopsis thaliana
. SAR has been observed in a wide range of flowering plants, including dicotyledon
and monocotyledon
species. SAR can be activated in corn, however, widely adapted commercial like Benzothiadiazole may not be efficient against P. sorghi causing common rust.
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
. SAR is analogous to the innate immune system
Innate immune system
The innate immune system, also known as non-specific immune system and secondary line of defence, comprises the cells and mechanisms that defend the host from infection by other organisms in a non-specific manner...
found in animals, and there is evidence that SAR in plants and innate immunity in animals may be evolutionarily conserved. SAR is important for plants to resist disease, as well as to recover from disease once formed. SAR can be induced by a wide range of pathogens, especially (but not only) those that cause tissue necrosis, and the resistance observed following induction of SAR is effective against a wide range of pathogens, which is why SAR resistance is sometimes called "broad spectrum." SAR is associated with the induction of a wide range of gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s (so called PR or "pathogenesis-related" genes), and the activation of SAR requires the accumulation of endogenous
Endogenous
Endogenous substances are those that originate from within an organism, tissue, or cell. Endogenous retroviruses are caused by ancient infections of germ cells in humans, mammals and other vertebrates...
salicylic acid
Salicylic acid
Salicylic acid is a monohydroxybenzoic acid, a type of phenolic acid and a beta hydroxy acid. This colorless crystalline organic acid is widely used in organic synthesis and functions as a plant hormone. It is derived from the metabolism of salicin...
(SA). The pathogen-induced SA signal activates a molecular signal transduction
Signal transduction
Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response...
pathway that is identified by a gene called NIM1, NPR1 or SAI1 (three names for the same gene) in the model genetic system Arabidopsis thaliana
Arabidopsis thaliana
Arabidopsis thaliana is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, arabidopsis is popular as a model organism in plant biology and genetics...
. SAR has been observed in a wide range of flowering plants, including dicotyledon
Dicotyledon
The dicotyledons, also known as dicots, are a group of flowering plants whose seed typically has two embryonic leaves or cotyledons. There are around 199,350 species within this group...
and monocotyledon
Monocotyledon
Monocotyledons, also known as monocots, are one of two major groups of flowering plants that are traditionally recognized, the other being dicotyledons, or dicots. Monocot seedlings typically have one cotyledon , in contrast to the two cotyledons typical of dicots...
species. SAR can be activated in corn, however, widely adapted commercial like Benzothiadiazole may not be efficient against P. sorghi causing common rust.