Eleanor Finch
CONSTITUTIVE TRIPLE RESPONSE 1 (CTR1) is a protein kinase that plays a crucial role in the phytohormone ethylene signaling pathway in plants. CTR1 is involved in regulating plant development, growth, and stress responses. It interacts with ethylene receptors and acts as a negative regulator, suppressing ethylene signaling in the absence of ethylene. CTR1 also plays a role in indeterminate root growth and meristem cell proliferation in Arabidopsis seedlings, coordinating the activity of important cellular processes. The binding of ethylene to its receptors inactivates CTR1, leading to the activation of downstream ETHYLENE INSENSITIVE 2 (EIN2) protein and subsequent transcriptional responses. CTR1 has been studied extensively in Arabidopsis thaliana, where it was initially identified through its effects on seedling and adult phenotypes.
| Characteristics | Values |
|---|---|
| Full Form | CONSTITUTIVE TRIPLE RESPONSE 1 |
| Abbreviation | CTR1 |
| Type | Protein kinase |
| Function | Negative regulator in the phytohormone ethylene signaling pathway |
| Interaction | Interacts with ethylene receptors via its N-terminal domain at the endoplasmic reticulum |
| Regulation | Suppresses ethylene signaling in the absence of ethylene |
| Phosphorylation | Directly phosphorylates the positive regulator ETHYLENE INSENSITIVE 2 (EIN2) |
| Role | Involved in regulating the movement of EIN2 into the nucleus |
| Evolution | Increase in the binding affinity of CTR1 and ethylene receptors during land-plant evolution |
| Expression | Loss-of-function results in a short root phenotype |
| Modulation | Modulates indeterminate root growth and meristem cell proliferating activity in Arabidopsis seedlings |
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What You'll Learn
- CTR1 is a Raf-like protein kinase
- CTR1 is a negative regulator in the phytohormone ethylene signalling pathway
- CTR1 directly interacts with and phosphorylates the positive regulator ETHYLENE INSENSITIVE 2 (EIN2)
- CTR1 is involved in suppressing ethylene signalling in the absence of ethylene
- CTR1 and PIN2 act in a coordinated manner to support indeterminate root growth
CTR1 is a Raf-like protein kinase
The plant hormone ethylene induces auxin biosynthesis and transport and modulates root growth and branching. CTR1 is a protein kinase that negatively regulates the ethylene response pathway in Arabidopsis thaliana. CTR1 is a Raf-like protein kinase that interacts with ETR1 and ERS and negatively regulates ethylene responses. The C-terminal domain of CTR1 is similar to the Raf family of protein kinases, but its first two-thirds encodes a novel protein domain. CTR1 physically interacts with ethylene receptors via its N-terminal domain at the endoplasmic reticulum, and is involved in suppressing ethylene signaling in the absence of ethylene. CTR1 phosphorylates EIN2, which encodes an Nramp homolog, whereas inhibition of CTR1 upon ethylene perception leads to cleavage and nuclear localization of the EIN2 C terminus, allowing the ethylene signal to reach the transcription factors EIN3 and ETHYLENE RESPONSE FACTOR (ERF). CTR1 acts via EIN2 to promote root cell division. CTR1 and PIN2 synergistically support indeterminate root growth. CTR1 alters expression of polar auxin transporters PIN1 and PIN2.
The binding of ethylene to ethylene receptors inactivates these receptors and, consequently, inactivates downstream CTR1. Inactivation of CTR1 permits the activation of the downstream ETHYLENE INSENSITIVE2 (EIN2) protein and the consequent activation of a transcriptional regulatory cascade consisting first of EIN3 and then of ERF-type transcription factors. CTR1 is a negative regulator in the phytohormone ethylene signaling pathway. CTR1 is involved in suppressing ethylene signaling in the absence of ethylene. Recent studies have demonstrated that CTR1 directly interacts with and differentially phosphorylates the positive regulator EIN2, therefore regulating the movement of EIN2 into the nucleus.
In addition, observations suggest that there has been an increase in the binding affinity of CTR1 and ethylene receptors during land-plant evolution, with the more recent Arabidopsis proteins (ethylene receptors, AtCTR1, and AtCRG) having relatively high affinities for one another when compared with the interaction between PpETR7 and PpCTR1L. The fact that AtCRG retained the ability to interact with ethylene receptors suggested a possible involvement of AtCRG in ethylene signaling. CTR1-like proteins have been found in other plants, such as the LeCTR2 protein kinase from tomato, which also plays a role in ethylene signalling, development, and defence.
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CTR1 is a negative regulator in the phytohormone ethylene signalling pathway
CONSTITUTIVE TRIPLE RESPONSE 1 (CTR1) is a protein kinase that functions as a negative regulator in the phytohormone ethylene signalling pathway. CTR1 is involved in suppressing ethylene signalling in the absence of ethylene. CTR1 physically interacts with ethylene receptors via its N-terminal domain at the endoplasmic reticulum. CTR1 is a Raf-like protein kinase, and its role as a negative regulator in the phytohormone ethylene signalling pathway has been observed in Arabidopsis thaliana and Arabidopsis plants.
The binding of ethylene to ethylene receptors inactivates these receptors and, consequently, inactivates CTR1. Inactivation of CTR1 permits the activation of the downstream ETHYLENE INSENSITIVE2 (EIN2) protein and the consequent activation of a transcriptional regulatory cascade. CTR1 phosphorylates EIN2, which encodes an Nramp homolog, whereas inhibition of CTR1 upon ethylene perception leads to cleavage and nuclear localization of the EIN2 C terminus, allowing the ethylene signal to reach transcription factors. CTR1 acts via EIN2 to promote root cell division.
The plant hormone ethylene induces auxin biosynthesis and transport and modulates root growth and branching. CTR1 alters the expression of polar auxin transporters PIN1 and PIN2. CTR1 and PIN2 act in a coordinate manner to support indeterminate root growth and meristem cell proliferating activity in Arabidopsis seedlings. CTR1 and PIN2 synergistically support indeterminate root growth.
Extensive molecular genetic studies have elucidated the basic ethylene signalling pathway. In the absence of ethylene, the endoplasmic reticulum (ER)-localized ethylene receptors activate CTR1, which in turn phosphorylates EIN2, an ER membrane-localized Nramp homolog that positively regulates ethylene responses. CTR1 directly phosphorylates the cytosolic C-terminal domain of EIN2. CTR1 is responsible for phosphorylating EIN2 in vivo, as this is consistent with CTR1 being an active kinase in the absence but not the presence of ethylene.
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CTR1 directly interacts with and phosphorylates the positive regulator ETHYLENE INSENSITIVE 2 (EIN2)
CONSTITUTIVE TRIPLE RESPONSE 1 (CTR1) is a protein kinase that functions as a negative regulator in the phytohormone ethylene signaling pathway. It interacts with ethylene receptors via its N-terminal domain at the endoplasmic reticulum, suppressing ethylene signaling in the absence of ethylene. CTR1 directly interacts with and phosphorylates the positive regulator ETHYLENE INSENSITIVE 2 (EIN2), an ER membrane-localized Nramp homolog that positively regulates ethylene responses. This phosphorylation regulates the movement of EIN2 into the nucleus.
The interaction between CTR1 and EIN2 is a critical component of the ethylene signaling pathway in plants. In the absence of ethylene, the receptors promote CTR1 kinase activity, which represses ethylene responses. CTR1 phosphorylates specific serine/threonine residues in the EIN2 C-terminal domain, preventing EIN2 from signaling. This phosphorylation of EIN2 by CTR1 is proposed to be the mechanism by which CTR1 represses ethylene responses when ethylene is absent.
When ethylene levels increase, the receptors, and consequently CTR1, become inactive. This inhibition of CTR1 upon ethylene perception allows for the cleavage and nuclear localization of the EIN2 C terminus, enabling the ethylene signal to reach downstream transcription factors. The activation of these transcription factors initiates a transcriptional regulatory cascade, leading to the activation of ETHYLENE RESPONSE FACTOR (ERF)-type transcription factors.
Genetic analyses have identified critical elements in ethylene signaling, but the biochemical interactions between these elements remain incompletely understood. Recent studies have focused on identifying the target of CTR1 and understanding the molecular events surrounding EIN2. By demonstrating that CTR1 directly interacts with and phosphorylates EIN2, these studies have advanced our understanding of the mechanisms underlying ethylene signal transduction.
Furthermore, observations in Physcomitrella patens suggest that CTR1 may have evolved from a dual regulator of both ethylene and abscisic acid signaling to its current role in land plants, where it primarily regulates ethylene signaling. This evolution is characterized by an increase in the binding affinity of CTR1 and ethylene receptors, optimizing their interaction.
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CTR1 is involved in suppressing ethylene signalling in the absence of ethylene
CONSTITUTIVE TRIPLE RESPONSE 1 (CTR1) is a Raf-like protein kinase that functions as a negative regulator in the phytohormone ethylene signalling pathway. CTR1 is involved in suppressing ethylene signalling in the absence of ethylene. CTR1 physically interacts with ethylene receptors via its N-terminal domain at the endoplasmic reticulum. CTR1 is activated by ethylene receptors and may require ECR2 for suppressing the ethylene response. CTR1 activation by ethylene receptors leads to the phosphorylation of the downstream signalling component ETHYLENE INSENSITIVE 2 (EIN2).
Phosphorylated EIN2 remains at the ER and cannot induce an ethylene response. With ethylene binding to ethylene receptors, the receptor signal output is prevented, and CTR1 is not activated. In the absence of ethylene, CTR1 inhibits downstream signalling through EIN2-mediated phosphorylation. CTR1 directly interacts with and differentially phosphorylates the positive regulator EIN2, regulating the movement of EIN2 into the nucleus. CTR1 acts via EIN2 to promote root cell division. CTR1 alters the expression of polar auxin transporters PIN1 and PIN2. CTR1 and PIN2 act in a coordinated manner to support indeterminate root growth and meristem cell proliferation activity in Arabidopsis seedlings.
The binding of ethylene to ethylene receptors inactivates these receptors and, consequently, inactivates CTR1. Inactivation of CTR1 permits the activation of the downstream EIN2 protein and the consequent activation of a transcriptional regulatory cascade consisting first of EIN3 and then of ETHYLENE RESPONSE FACTOR (ERF)-type transcription factors. CTR1 expression is induced by ethylene and is suppressed in ethylene-insensitive mutant backgrounds. CTR1 expression is regulated by downstream components of the ethylene signal transduction pathway. CTR1 is a crucial component in the ethylene signalling pathway, transmitting signals perceived by ethylene receptors to downstream EIN2 proteins through phosphorylation/dephosphorylation.
Ethylene is perceived by receptor-related histidine kinases, which reside at the endoplasmic reticulum and interact with CTR1. In the absence of ethylene, the receptors promote CTR1 kinase activity via phosphorylation, which represses ethylene responses. When ethylene levels increase, the receptors and, therefore, CTR1 are inactive. Once an ethylene molecule binds to the receptor, it becomes desensitized as both its binding and kinase activity shut off. CTR1 phosphorylates EIN2, which encodes an Nramp homolog, whereas inhibition of CTR1 upon ethylene perception leads to cleavage and nuclear localization of the EIN2 C terminus, allowing the ethylene signal to reach the transcription factors EIN3 and ERF.
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CTR1 and PIN2 act in a coordinated manner to support indeterminate root growth
CONSTITUTIVE TRIPLE RESPONSE 1 (CTR1) is a protein kinase that functions as a negative regulator in the phytohormone ethylene signalling pathway. CTR1 physically interacts with ethylene receptors and is involved in suppressing ethylene signalling in the absence of ethylene. CTR1 directly interacts with and phosphorylates the positive regulator ETHYLENE INSENSITIVE 2 (EIN2), regulating its movement into the nucleus. The binding of ethylene to ethylene receptors inactivates CTR1, permitting the activation of EIN2 and subsequent activation of a transcriptional regulatory cascade.
The plant hormone ethylene induces auxin biosynthesis and transport, modulating root growth and branching. CTR1 and PIN2 act in a coordinated manner to support indeterminate root growth and meristem cell proliferating activity in Arabidopsis seedlings. CTR1 loss-of-function results in a short root phenotype due to inhibited cell division and elongation. This is associated with increased expression of the auxin transporter PIN2 and decreased expression of key factors for stem cell niche maintenance, such as PLETHORA1, SHORTROOT, and SCARECROW. CTR1 alters the expression of polar auxin transporters PIN1 and PIN2, and its loss-of-function affects the root stem cell niche.
PIN proteins, including PIN1 and PIN2, function as auxin efflux facilitators, and their asymmetric apical-basal targeting determines the rate and direction of auxin flux. Root gravitropism allows roots to grow downward into the soil for better absorption of nutrients and water, and it is regulated by the asymmetric transport of auxin. The peptidyl-prolyl cis/trans isomerase Pin1At contributes to root gravitropism by altering the polarity of the PIN1 auxin transport protein. Pin1At affects the conformational dynamics of PIN1 and the regulation of its phosphorylation, impacting auxin transport and polar localisation.
In summary, CTR1 and PIN2 act synergistically to support indeterminate root growth by regulating cell division and elongation. CTR1's role in the ethylene signalling pathway influences auxin biosynthesis and transport, while PIN2 regulates shootward auxin transport and root gravitropism. The coordinated action of CTR1 and PIN2 ensures proper root growth and patterning, maintaining the balance between ethylene and auxin signalling.
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Frequently asked questions
CTR1 is a protein kinase that functions as a negative regulator in the phytohormone ethylene signaling pathway.
CTR1 physically interacts with ethylene receptors via its N-terminal domain at the endoplasmic reticulum, and is involved in suppressing ethylene signaling in the absence of ethylene.
Inactivation of CTR1 permits the activation of the downstream ETHYLENE INSENSITIVE2 (EIN2) protein and the consequent activation of a transcriptional regulatory cascade.
CTR1 and PIN2 act in a coordinated manner to support indeterminate root growth and meristem cell-proliferating activity in Arabidopsis seedlings. CTR1 loss-of-function results in a short root phenotype.
