Plant Development Week 5 class notes
Plant Development Week 5 class notes bio 523
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CH 105 - 1D
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This 6 page Class Notes was uploaded by carte226 on Thursday October 13, 2016. The Class Notes belongs to bio 523 at University of South Carolina taught by Dr. Krizek in Fall 2016. Since its upload, it has received 4 views. For similar materials see Plant Development in Plant Biology at University of South Carolina.
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Date Created: 10/13/16
Ethylene Signaling Plant hormones/ phytohormones/ plant growth regulators - Small molecules that regulate plant growth and development - Active at low concentration 10^-6 – 10^M - Can act locally at the site of synthesis or at more distanct locations - Exist in free and conjugated forms - Intensity of plant’s response to a hormone depends on both the conc of the hormone and tissue sensitivity to the hormone - Many processes in plants are controlled by multiple hormones (synergistic; antagonistic) 5 Classical hormones: 1. Ethylene a. Promotes: i. fruit ripening ii. Organ abscission iii. Organ senescence b. Economics: i. Shelf life of cup ripening fruits and cut flowers 2. Auxin 3. Cytokinin 4. Gibberellins 5. Abscisic Acid Other hormones: brassinosteriods, jasmonic acid, Ethylene Genetic screens to identify genes involved in ethylene signaling - Based on ‘triple response’ phenotype that is exhibited by seedlings that are grown in the dark in the presence of ethylene - Triple response: o inhibition of shoot and root elongation (shoot hypocotyl) o Swelling of hypocotyl o Exaggerated apical hook Genetic screens: 1. Germinate the M2 generation in the dark in the presence of ethylene and look for those mutants that lack the triple response o Ethylene insensitive mutants (ein) o Ethylene resistant mutants (etr) ^^ some of the mutants were dominant in ein and etr 2. Germinate the M2 seeds in the dark in the absence of ethylene and look for utants that gave the triple response Ethylene over-producers (eto) Consititutive triple response (ctr1) ^^^ mutants were recessive in eto and ctr1 ETR1: 4 dominant alleles generated Etr1-1 etr1-2 etr1-3 etr1-4 Lacked many ethylene responses DO NOT KNOW IF ETR1 IS A POSITIVE OR A NEGATIVE REGULATOR OF ETHYLENE RESPONSES ETR1 protein: protein is similar to a bacterial component histidine kinases Two component signaling system is bacteria: - Control adaptive responses to many different environmental stimuli ) chemotaxis; adaptation to osmolarity; host recognition) Classical two components system in bacteria consists of two proteins: 1. Sensor (detects signal) 2. Response regulator (promotes biological response; change in gene expression) Make up short signaling pathway Sensor Input -------(transmembrane protein)--------- His Kinase P (extracellular) (Intracellular) Response regulator D-P Receiver------------ output (transcription regulator) D = aspartic acid Steps in Signaling: 1. Input domain perceives signal 2. Autphosphorylation of HIS Kinase 3. Phosphate group is transferred to Asp (D) on the receiver domain of the response regulator 4. Activation of the output domain Output domain is often transcription regulator Response: change in gene expression ETR1: hybrid histidine kinase Input His Kinase receiver ETR1 is an ethylene receptor - Binds ethylene through its input domain (copper cofactor) ETR1 can homodimerize ETR1 protein is localized to the ER membrane His Kinase can autophosphorylate but this activity is not required for signaling but can modulate the response Mutations in the input domain for etr1-1, etr1-2, etr1-3, etr1-4 Mutant proteins encoded by these alleles cannot bind ethylene Ethylene receptor family: - Arabisopsis have 5 ethylene receptors: ETR1, ERS1, ERS2, ETR2, EIN4 - Fall into two subfamilies: o Subfamily I: ETR1, ERS2 3 hydrophobic membrane spanning domains HIS Kinase domain o Subfamily II: ERS2, ETR2, EIN4 4 hydrophobic membrane spanning domains HIS Kinase domain lacks critical amino acids and lacks kinase activity ETR1, ETR2, EIN4 – all possess receiver domain - Different receptors can interact with each other to form multimeric receptor complexes Genetic redundancy: occurs when a particular biochemical function can be performed by proteins encoded by two or more genes The reason no loss LOF (recessive) mutations in ETR1 were identified in forward genetic screens was due to genetic redundancy Etr1 LOF phenotype: WT appearance when grown in the dark in ethylene Reverse genetics: identify LOF alleles in each of the ethylene receptors and made higher order mutants to determine the role of ethylene receptors in ethylene signaling Ctrl: mutant with a constitutive triple response phenotype - Not reversible if the seedlings were treated with inhibitors of ethylene biosynthesis - Recessive CTR1: WT fn is to repress ethylene responses in the absence of ethylene CTR1 protein is a ser/Thr Kinase with homology to mammalian protein Raf (MAPKKK= MAP Kinase Kinase Kinase) MAP= mitogen activated protein MAPK cascade: involves a series of 3 kinases that act in a sequential manner in a signal transduction pathway (relay the signal from the receptor complex to the nucleus CTR1 does not work in a MAPK casscade CTR1: homodimerize upon activation present at ER membrane due to association with ethylene receptor - N terminal part of CTR1 interacts with HIS Kinase domain of receptors - This association is important for induction of CTR1’s kinase activity
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