Plant Signaling Pathways Quiz

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Questions and Answers

Which plant hormone was the first known plant hormone?

Indole-3-acetic acid (IAA)

What experiment by Charles Darwin and his son Francis led to the concept of plant hormones?

Experiment on phototropism

Which of the following is not a plant hormone?

Growth hormone

Which group of plant hormones bear little resemblance to their animal counterparts?

Brassinosteroids (BRs) Signup and view all the answers

What promotes differential cell elongation in the lower parts of the seedling resulting in it bending toward the light source?

Indole-3-acetic acid (IAA) Signup and view all the answers

What are the relatively simple, small molecules such as ethylene gas and indole-3-acetic acid (IAA) collectively called?

Phytohormones Signup and view all the answers

What is the notable exception among the steroidal hormones in the plant hormones group?

Brassinosteroids (BRs) Signup and view all the answers

What is the role of the SHAGGY/GSK3-type kinase BIN2 in the BR signaling pathway?

It phosphorylates the transcription factors BES1 and BZR1, targeting them for proteolysis by the 26S proteasome. Signup and view all the answers

What did Nemhauser and colleagues demonstrate about the regulation of Arabidopsis hypocotyl elongation by auxin and BR?

Auxin and BR regulate hypocotyl elongation in a synergistic and interdependent fashion. Signup and view all the answers

What remains to be identified for the majority of phytohormones, according to the text?

Receptors and other upstream signaling components. Signup and view all the answers

What is the role of BRI1 in the BR signaling pathway?

It is involved in perceiving the BR signal at the cell surface. Signup and view all the answers

What happens to BES1 and BZR1 upon a BR stimulus?

They accumulate in the nucleus. Signup and view all the answers

What effect does elevating endogenous auxin levels have on plants in hypocotyl elongation assays?

It makes plants more sensitive to BR application. Signup and view all the answers

What is BIN2's role in the absence of a BR signal?

It phosphorylates transcription factors BES1 and BZR1, targeting them for proteolysis by the 26S proteasome. Signup and view all the answers

What do genetic studies suggest about the convergence of auxin and BR pathways?

It occurs at a late point in hormone signaling. Signup and view all the answers

What do bioinformatic analysis identify specifically in the promoters of auxin-induced, BR-induced, and auxin/BR-induced genes?

Distinct sequence elements enriched specifically in promoters of auxin/BR-induced genes. Signup and view all the answers

Which type of receptor proteins are typically found in bacterial two-component systems?

Histidine kinase (HK) domain receptors Signup and view all the answers

Which receptors function as negative regulators of the ethylene pathway?

ETR1 and ERS1 Signup and view all the answers

Which protein is a positive regulator of ethylene signaling?

EIN2 Signup and view all the answers

What stabilizes EIN3 and EIL1, preventing their degradation in the absence of ethylene?

Ethylene Signup and view all the answers

At which point do the ethylene and JA signaling pathways converge?

Transcription factor ERF1 Signup and view all the answers

Which signaling pathways appear to converge and mutually regulate some developmental processes?

Auxin and BR signaling pathways Signup and view all the answers

Where are histidine kinase (HK) domains typically found?

In bacterial two-component systems Signup and view all the answers

What is the function of Ethylene in plants?

Promotes fruit ripening, senescence, and responses to pathogens and abiotic stresses Signup and view all the answers

Which hormone promotes seed dormancy and is involved in stress signaling pathways in plants?

Abscisic Acid (ABA) Signup and view all the answers

What do Cytokinins regulate in plants?

Promotes cytokinesis Signup and view all the answers

What is the function of Gibberellins (GAs) in plants?

Promotes germination, stem elongation, and induction of flowering Signup and view all the answers

What is a common theme in plant hormone signaling?

Ubiquitin-mediated degradation of key regulatory proteins Signup and view all the answers

What mechanism does Auxin use to regulate SCF–substrate interactions?

Auxin-induced modification of Aux/IAA proteins Signup and view all the answers

What does the axr2-1 mutant do in relation to auxin response?

Constitutively represses auxin response due to the inability to be targeted for proteolysis Signup and view all the answers

Study Notes

Plants hormones include Ethylene, IAA (Auxin), Cytokinins, JA, BRs, and ABA. Each hormone has distinct functions.
Ethylene promotes fruit ripening, senescence, and responses to pathogens and abiotic stresses.
IAA (Auxin) regulates cell division and expansion, vascular differentiation, lateral root development, and apical dominance.
Cytokinins were first identified by their ability to promote cytokinesis.
JA is a volatile signal that modulates pollen development and responses to pathogen infection.
BRs regulate cell expansion and photomorphogenesis (light-regulated development).
GAs are diterpenoid compounds that promote germination, stem elongation, and the induction of flowering.
ABA promotes seed dormancy and is involved in several stress signaling pathways.
Hormonal control plays a role in virtually every aspect of plant growth and development.
A single hormone can regulate multiple processes, while multiple hormones can influence a single process.
The effects of each hormone have historically been defined by applying exogenous hormones.
The discovery of hormone biosynthetic and response mutants has provided new insights into phytohormone roles.
The molecular mechanisms behind phytohormone action are being elucidated through genetics and molecular analysis.
Ubiquitin-mediated degradation of key regulatory proteins is a common theme in plant hormone signaling.
Auxin uses a novel mechanism to regulate SCF–substrate interactions.
The axr2-1 mutant is a dominant gain-of-function mutation in an Aux/IAA gene, which confers reduced auxin response due to the inability to be targeted for proteolysis by the SCFTIR1 ubiquitin ligase.
The Ubiquitin-Mediated Proteolysis of Aux/IAA Proteins Regulates Auxin Response.
The SCFTIR1 ubiquitin ligase ubiquitinates the Aux/IAA proteins, marking them for degradation.
The hormone promotes Aux/IAA–TIR1 interaction, but the molecular mechanisms behind this regulation are unclear.
Auxin-induced modification of Aux/IAA proteins has not been discovered.
The axr2-1 protein constitutively represses auxin response due to the inability to be targeted for proteolysis.
The effect of the mutation on AXR2 stability has been demonstrated through a pulse-chase experiment.

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