Systemic acquired resistance
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 although there are many shared aspects between the two systems, it is thought to be a result of convergent evolution.[1] The systemic acquired resistance response is dependent on the plant hormone, salicylic acid.
Discovery
While, it has been recognized since at least the 1930s that plants have some kind of induced immunity to pathogens, the modern study of systemic acquired resistance began in the 1980s when the invention of new tools allowed scientists to probe the molecular mechanisms of SAR.
The first plant receptors of conserved microbial signatures were identified in rice (XA21, 1995)[3] and in Arabidopsis (FLS2, 2000).[4]
Mechanism
Plants have several immunity mechanisms to deal with infections and stress. When they are infected with pathogens the immune system recognizes called pathogen-associated molecular patterns (PAMPs), it is via pattern recognition receptors (PRRs). This induces a PAMP-triggered immunity (PTI). Some pathogens carry effectors that suppress PTI in the plant and induce effector triggered susceptibility (ETS). In response, plants evolve resistance (R) genes that encode for proteins capable of recognizing the newly developed pathogen effectors, resulting in what is called effector triggered immunity (ETI). ETI often results in a form of programmed cell death (PCD), called hypersensitive response (HR). Pathogens can then evolve and develop new effectors for overcoming ETI, to which plants can respond by developing new R genes capable of recognizing the pathogen effector, thereby providing a new ETI. When PTI and ETI are activated in the local infected plant tissues, there is a signaling cascade that induces an immune response throughout the whole plant. This "whole plant" immune response is called systemic acquired resistance (SAR). SAR is characterized by accumulation of plant metabolites and genetic reprogramming both locally and systemically (surrounding tissues that were not infected). Salicylic acid (SA) and N-hydroxypipecolic acid (NHP) are two metabolites that have been shown to accumulate during SAR. Plants with reduced or no production of SA and Pip (a precursor to NHP) have been shown to exhibit reduced or no SAR response following infection.
Use in disease control
Unusually, the synthetic fungicide acibenzolar-S-methyl is not directly toxic to pathogens, but rather acts by inducing SAR in the crop plants to which it is applied. It is a propesticide — converted in-vivo into 1,2,3-benzothiadiazole-7-carboxylic acid by methyl salicylate esterase.[5] Field trials have found that acibenzolar-S-methyl (also known as BSA)[citation needed] is effective at controlling some plant diseases, but may have little effect on others, especially fungal pathogens which may not be very susceptible to SAR.[6]
See also
References
Chuanfu et al, A. (2011). Salicylic acid and its function in plant immunity. Conrath, U. (2006). Systemic Acquired Resistance. Plant Signaling and Behavior. Deng et al, C. (2003). Rapid Determination of Salicylic Acid in Plant Materials by Gas Chromatography–Mass Spectrometry. Chromatographia. Holmes et al, E. C. (2019). An engineered pathway for N-hydroxy-pipecolic acid synthesis enhances systemic acquired resistance in tomato. Sci Signal. Huang et al, W. (2020). Biosynthesis and Regulation of Salicylic Acid and N-Hydroxypipecolic Acid in Plant Immunity. Molecular Plant.
Further reading
- Miller G, Schlauch K, Tam R, Cortes D, Torres MA, Shulaev V, Dangl JL, Mittler R (August 2009). "The plant NADPH oxidase RBOHD mediates rapid systemic signaling in response to diverse stimuli". Science Signaling. 2 (84): ra45. S2CID 7717692.
- Ryals JA, Neuenschwander UH, Willits MG, Molina A, Steiner HY, Hunt MD (October 1996). "Systemic Acquired Resistance". The Plant Cell. 8 (10): 1809–1819. PMID 12239363.
External links
- "Exploiting Plants' Protective Proteins". KeyPlex. 2010. Archived from the original on 2010-11-15.
- "systemic-acquired-resistancesar-and-its-significance-in-plant-disease-management". 2018.