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Questions and Answers
Plant hormones include only auxin, cytokinin, and gibberellins
Plant hormones include only auxin, cytokinin, and gibberellins
False
The concept of plant hormones originated from an experiment on phototropism conducted by Charles Darwin and his son Francis in 1880
The concept of plant hormones originated from an experiment on phototropism conducted by Charles Darwin and his son Francis in 1880
True
Plant hormones are structurally similar to their animal counterparts
Plant hormones are structurally similar to their animal counterparts
False
Ethylene gas and indole-3-acetic acid (IAA) are examples of relatively simple, small molecules that act as plant hormones
Ethylene gas and indole-3-acetic acid (IAA) are examples of relatively simple, small molecules that act as plant hormones
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The bending of plants toward light, known as phototropism, is regulated by the hormone abscisic acid (ABA)
The bending of plants toward light, known as phototropism, is regulated by the hormone abscisic acid (ABA)
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BR-induced genes are also up-regulated by auxin
BR-induced genes are also up-regulated by auxin
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The absence of a BR signal leads to the accumulation of BES1 and BZR1 in the nucleus
The absence of a BR signal leads to the accumulation of BES1 and BZR1 in the nucleus
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Elevating endogenous auxin levels makes plants less sensitive to BR application in hypocotyl elongation assays
Elevating endogenous auxin levels makes plants less sensitive to BR application in hypocotyl elongation assays
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The convergence of auxin and BR pathways occurs at an early point in hormone signaling
The convergence of auxin and BR pathways occurs at an early point in hormone signaling
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The majority of the phytohormones have identified receptors and other upstream signaling components
The majority of the phytohormones have identified receptors and other upstream signaling components
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Ethylene receptors ETR1 and ERS1 have intact HK domains, while ETR2, ERS2, and EIN4 have degenerate HK domains and lack catalytic activity
Ethylene receptors ETR1 and ERS1 have intact HK domains, while ETR2, ERS2, and EIN4 have degenerate HK domains and lack catalytic activity
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Mutations in ethylene receptors confer dominant ethylene insensitivity, suggesting they function as negative regulators upstream of CTR1
Mutations in ethylene receptors confer dominant ethylene insensitivity, suggesting they function as negative regulators upstream of CTR1
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Ethylene signal transduction involves a MAP kinase cascade and positive regulators EIN2, EIN3, and EIL1
Ethylene signal transduction involves a MAP kinase cascade and positive regulators EIN2, EIN3, and EIL1
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Ethylene binds to receptors inactivating them, leading to down-regulation of CTR1 activity
Ethylene binds to receptors inactivating them, leading to down-regulation of CTR1 activity
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Auxin and brassinosteroid (BR) signaling pathways converge and regulate each other in some developmental processes
Auxin and brassinosteroid (BR) signaling pathways converge and regulate each other in some developmental processes
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Ethylene promotes leaf expansion and vascular differentiation in plants.
Ethylene promotes leaf expansion and vascular differentiation in plants.
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The green revolution in the 20th century utilized genetically modified tall varieties of wheat and rice.
The green revolution in the 20th century utilized genetically modified tall varieties of wheat and rice.
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Cytokinins were initially discovered for their ability to inhibit cell division during cytokinesis.
Cytokinins were initially discovered for their ability to inhibit cell division during cytokinesis.
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ABA promotes seed dormancy and inhibits stress signaling pathways in plants.
ABA promotes seed dormancy and inhibits stress signaling pathways in plants.
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Aux/IAA proteins prevent the activity of ARF transcription factors in the presence of auxin stimulus.
Aux/IAA proteins prevent the activity of ARF transcription factors in the presence of auxin stimulus.
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Study Notes
- Plants use hormones for various aspects of growth and development, with each hormone eliciting specific responses.
- Ethylene promotes fruit ripening, senescence, and responses to pathogens and abiotic stresses.
- IAA (auxin) regulates cell division, expansion, vascular differentiation, lateral root development, and apical dominance.
- Cytokinins were first identified for their ability to promote cell division during cytokinesis.
- JA is a volatile signal that modulates pollen development and responses to pathogen infection.
- BRs regulate cell expansion and light-regulated development.
- GAs promote germination, stem elongation, and induction of flowering.
- ABA promotes seed dormancy and involves several stress signaling pathways.
- Historically, hormonal effects have been defined by the application of exogenous hormones, but recent research has used hormone biosynthetic and response mutants to gain a clearer understanding of their roles.
- The green revolution in the 20th century used genetically modified dwarf varieties of wheat and rice, which had shorter stems and were less susceptible to damage from weather, leading to the isolation of GA biosynthesis and response pathways.
- Arabidopsis thaliana, a genetically facile model plant, has been used to isolate mutations that confer altered response to applied hormones.
- Several hormone pathways have been reviewed for further information.
- Regulation by proteolysis has emerged as a major theme in plant hormone signaling, with key regulatory proteins being ubiquitinated and degraded.
- Auxin response is regulated by the Aux/IAA proteins, which form heterodimers with ARF transcription factors and prevent their activity.
- Upon auxin stimulus, the Aux/IAA proteins are targeted to the SCFTIR1 complex, resulting in their ubiquitination and degradation by the 26S proteasome, thereby de-repressing the ARF transcription factors.
- The auxin stimulus promotes the Aux/IAA–TIR1 interaction.
- Most yeast and animal SCF substrates are post-translationally modified, usually by phosphorylation, before they are recognized by their cognate F-box protein, but no such modification has been identified for auxin-induced modification of Aux/IAA proteins.
- The mechanism by which auxin regulates SCF–substrate interactions is unknown.
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Description
Test your knowledge of plant signaling pathways with this quiz. Explore topics such as ARF targets, Aux/IAA genes, ethylene, cytokinin, and eukaryotic modular signaling systems.
