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Arabidopsis thaliana, the thale cress, mouse-ear cress or arabidopsis, is a small plant from the mustard family (Brassicaceae), native to Eurasia and Africa. Commonly found along the shoulders of roads and in disturbed land, it is generally considered a weed.
Flagellin is a globular protein that arranges itself in a hollow cylinder to form the filament in a bacterial flagellum. It has a mass of about 30,000 to 60,000 daltons. Flagellin is the principal component of bacterial flagella, and is present in large amounts on nearly all flagellated bacteria.
Pathogen-associated molecular patterns (PAMPs) are small molecular motifs conserved within a class of microbes, but not present in the host. They are recognized by toll-like receptors (TLRs) and other pattern recognition receptors (PRRs) in both plants and animals. This allows the innate immune system to recognize pathogens and thus, protect the host from infection.
Pattern recognition receptors (PRRs) play a crucial role in the proper function of the innate immune system. PRRs are germline-encoded host sensors, which detect molecules typical for the pathogens. They are proteins expressed mainly by cells of the innate immune system, such as dendritic cells, macrophages, monocytes, neutrophils, as well as by epithelial cells, to identify two classes of molecules: pathogen-associated molecular patterns (PAMPs), which are associated with microbial pathogens, and damage-associated molecular patterns (DAMPs), which are associated with components of host's cells that are released during cell damage or death. They are also called primitive pattern recognition receptors because they evolved before other parts of the immune system, particularly before adaptive immunity. PRRs also mediate the initiation of antigen-specific adaptive immune response and release of inflammatory cytokines.
The innate immune system or nonspecific immune system is one of the two main immunity strategies in vertebrates. The innate immune system is an alternate defense strategy and is the dominant immune system response found in plants, fungi, prokaryotes, and invertebrates.
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. The systemic acquired resistance response is dependent on the plant hormone, salicylic acid.
Hypersensitive response (HR) is a mechanism used by plants to prevent the spread of infection by microbial pathogens. HR is characterized by the rapid death of cells in the local region surrounding an infection and it serves to restrict the growth and spread of pathogens to other parts of the plant. It is analogous to the innate immune system found in animals, and commonly precedes a slower systemic response, which ultimately leads to systemic acquired resistance (SAR). HR can be observed in the vast majority of plant species and is induced by a wide range of plant pathogens such as oomycetes, viruses, fungi and even insects.
The gene-for-gene relationship is a concept in plant pathology that plants and their diseases each have single genes that interact with each other during an infection. It was proposed by Harold Henry Flor who was working with rust (Melampsora lini) of flax (Linum usitatissimum). Flor showed that the inheritance of both resistance in the host and parasite ability to cause disease is controlled by pairs of matching genes. One is a plant gene called the resistance (R) gene. The other is a parasite gene called the avirulence (Avr) gene. Plants producing a specific R gene product are resistant towards a pathogen that produces the corresponding Avr gene product. Gene-for-gene relationships are a widespread and very important aspect of plant disease resistance. Another example can be seen with Lactuca serriola versus Bremia lactucae.
The nucleotide-binding oligomerization domain-like receptors, or NOD-like receptors (NLRs), are intracellular sensors of pathogen-associated molecular patterns (PAMPs) that enter the cell via phagocytosis or pores, and damage-associated molecular patterns (DAMPs) that are associated with cell stress. They are types of pattern recognition receptors (PRRs), and play key roles in the regulation of innate immune response. NLRs can cooperate with toll-like receptors (TLRs) and regulate inflammatory and apoptotic response.
Biotic stress is stress that occurs as a result of damage done to an organism by other living organisms, such as bacteria, viruses, fungi, parasites, beneficial and harmful insects, weeds, and cultivated or native plants. It is different from abiotic stress, which is the negative impact of non-living factors on the organisms such as temperature, sunlight, wind, salinity, flooding and drought. The types of biotic stresses imposed on an organism depend the climate where it lives as well as the species' ability to resist particular stresses. Biotic stress remains a broadly defined term and those who study it face many challenges, such as the greater difficulty in controlling biotic stresses in an experimental context compared to abiotic stress.
Plant disease resistance protects plants from pathogens in two ways: by pre-formed structures and chemicals, and by infection-induced responses of the immune system. Relative to a susceptible plant, disease resistance is the reduction of pathogen growth on or in the plant, while the term disease tolerance describes plants that exhibit little disease damage despite substantial pathogen levels. Disease outcome is determined by the three-way interaction of the pathogen, the plant and the environmental conditions.
Effector-triggered immunity (ETI) is one of the pathways, along with the pattern-triggered immunity (PTI) pathway, by which the innate immune system recognises pathogenic organisms and elicits a protective immune response. ETI is elicited when an effector protein secreted by a pathogen into the host cell is successfully recognised by the host. Alternatively, effector-triggered susceptibility (ETS) can occur if an effector protein can block the immune response triggered by pattern recognition receptors (PRR) and evade immunity, allowing the pathogen to propagate in the host.
Guard theory is a branch of immunology which concerns the innate sensing of stereotypical consequences of a virulence factor or pathogen. This is in contrast to the classical understanding of recognition by the innate immune system, which involves recognition of distinct microbial structures- pathogen-associated molecular patterns (PAMPs)- with pattern recognition receptors (PRRs). Some of these stereotypical consequences of virulence factors and pathogens may include altered endosomal trafficking and changes in the cytoskeleton. These recognition mechanisms would work to complement classical pattern recognition mechanisms.
Mitogen-activated protein kinase (MAPK) networks are the pathways and signaling of MAPK, which is a protein kinase that consists of amino acids serine and threonine. MAPK pathways have both a positive and negative regulation in plants. A positive regulation of MAPK networks is to help in assisting with stresses from the environment. A negative regulation of MAPK networks is pertaining to a high quantity of reactive oxygen species (ROS) in the plant.
Leucine-rich repeat receptor like protein kinase are plant cell membrane localized Leucine-rich repeat (LRR) receptor kinase that play critical roles in plant innate immunity. Plants have evolved intricate immunity mechanism to combat against pathogen infection by recognizing Pathogen Associated Molecular Patterns (PAMP) and endogenous Damage Associated Molecular Patterns (DAMP). PEPR 1 considered as the first known DAMP receptor of Arabidopsis.
EF-Tu receptor, abbreviated as EFR, is a pattern-recognition receptor (PRR) that binds to the prokaryotic protein EF-Tu in Arabidopsis thaliana. This receptor is an important part of the plant immune system as it allows the plant cells to recognize and bind to EF-Tu, preventing genetic transformation by and protein synthesis in pathogens such as Agrobacterium.
High Affinity K+ transporter HAK5 is a transport protein found on the cell surface membrane of plants under conditions of potassium deprivation. It is believed to act as a symporter for protons and the potassium ion, K+. Firstly discovered in barley, receiving the name of HvHAK1, it was soon after identified in the model plant Arabidopsis thaliana and named HAK5. These transporters belongs to the subgroup I of the KT-HAK-KUP family of plant proteins with obvious homology with both bacterial and fungal transport systems, which experienced a major diversification following land conquest. KT-HAK-KUP transporters are one of four different types of K+ transporter within the cell, but are unique as they do not have a putative pore forming domain like the other three; Shaker channels, KCO channels, HKT transporters. It is activated when the plant is situated in low soil with low potassium concentration, and has been shown to be located in higher concentration in the epidermis and vasculature of K+ deprived plants. By turning on, it increases the plants affinity (uptake) of potassium. Potassium plays a vital role in the plants growth, reproduction, immunity, ion homeostasis, and osmosis, which ensures the plants survival. It is the highest cationic molecule within the plant, accounting for 10% of the plants dry weight, which makes its uptake into the plant important. Each plant species has its own HAK5 transporter that is specific to that species and has different levels of affinity to K+. To operate and activate the HAK5 transporter, the external concentration of K+ must be lower than 10μM and up to 200μM. In Arabidopsis plants, when external potassium concentration is lower than 10μM, it is only HAK5 that is involved with the uptake of K+, then between 10 and 200μM both HAK5 and AKT1 are involved with the uptake of K+. HAK5 is coupled with CBL9/CIPK23 kinase's although the mechanism behind this has not yet been understood.
Botrytis–induced kinase 1 (BIK1) is a membrane-anchored enzyme in plants. It is a kinase that provides resistance to necrotrophic and biotrophic pathogens. As its name suggests, BIK1 is only active after being induced by Botrytis infection. When Botrytis cinerea is present, the BIK1 gene is transcribed so that the kinase is present to defend the cell. BIK1 functions to regulate the amount of salicylic acid (SA) present in the cell. When Botrytis cinerea or Alternaria brassicicola or any other necrotrophic pathogen is present, BIK1 is transcribed to regulate the pathogen response mechanisms. When BIK1 is present, SA levels decrease, allowing the nectrotrophic response to take place. When nectrotrophic pathogens are not present, BIK1 is not transcribed and SA levels increase, limiting the necrotrophic resistance pathway. Only the pathogenic defense response that is initiated by BIK1 is dependent on SA levels. Non-pathogenic cellular functions occur independently. In terms of non-pathogenic cellular functions, BIK1 is described as a critical component of ET signaling and PAMP-triggered immunity to pathogens.
PEPR 1 and PEPR2 are homolog kinases that act as enzymes on other proteins. They attach a phosphate group to specific proteins, called phosphorylation. These reactions can cause the function of the phosphorylated proteins to change. Both PEPR 1 and PEPR 2 can be classified as receptor kinases, which serve an important role in immunity in plants. Receptor kinases have the ability to change the conformation of receptors by adding the phosphate group. These specific receptor kinases serve as a pattern recognition receptor, or PRR, that can quickly and efficiently recognize many different molecular patterns or signatures that are unique to each pathogen. They can also detect different danger signals released from the host and respond accordingly. More specifically, the proteins contain leucine-rich repeat segments that interact outside of the cell. This leucine-rich repeat is a structural motif present in some proteins that has specific functions due to its folded structure. This fold can contain many repeating amino acids, but the most common is the hydrophobic leucine, hence the name. PEPR1 and PEPR2 are present in plants and are involved in several immune system processes. Their ability to change the conformation of receptors can have an effect on signaling processes within plants, allowing the plant to have a system of immunity in place in case of an infection or pathogen.
Fungal effectors are proteins or non-proteinaceous molecules secreted by pathogenic fungi into a host organism in order to modulate the host's immune response.
References
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- ↑ Knepper C, Day B (2010). "From perception to activation: the molecular-genetic and biochemical landscape of disease resistance signaling in plants". The Arabidopsis Book. 8: e012. doi:10.1199/tab.0124. PMC 3244959 . PMID 22303251.
- 1 2 Hafeez AN, Arora S, Ghosh S, Gilbert D, Bowden RL, Wulff BB (July 2021). "Creation and judicious application of a wheat resistance gene atlas" (PDF). Molecular Plant. Cell Press. 14 (7): 1053–1070. doi: 10.1016/j.molp.2021.05.014 . PMID 33991673. S2CID 234683221.
- ↑ Lapin D, Bhandari DD, Parker JE (August 2020). "Origins and Immunity Networking Functions of EDS1 Family Proteins". Annual Review of Phytopathology. Annual Reviews. 58 (1): 253–276. doi:10.1146/annurev-phyto-010820-012840. PMID 32396762. S2CID 218617308.
