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Stress-Responsive Genes
MCQ questions and answers.
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MCQ Questions
1. During drought stress, abscisic acid activates a transcriptional response primarily by promoting which regulatory sequence of events?
A.
ABA binds PYR/PYL receptors, inhibits PP2C phosphatases, and permits SnRK2 activation of stress-responsive transcription factors
B.
ABA binds directly to DNA and functions as the transcription factor for drought-response genes
C.
ABA activates protein phosphatases that permanently inhibit all stress-responsive transcription factors
D.
ABA prevents SnRK2 kinases from phosphorylating transcription factors, thereby increasing gene expression indirectly
Correct Answer:
ABA binds PYR/PYL receptors, inhibits PP2C phosphatases, and permits SnRK2 activation of stress-responsive transcription factors
Explanation:
ABA signaling through PYR/PYL receptors, PP2C inhibition, and SnRK2 activation leads to phosphorylation of transcription factors such as AREB/ABF, which regulate ABA-responsive stress genes.
2. Which transcription factor is most directly associated with activation of many ABA-responsive genes through ABRE promoter elements?
A.
AREB/ABF
B.
DREB2
C.
TCP
D.
MADS-box
Correct Answer:
AREB/ABF
Explanation:
AREB/ABF transcription factors bind ABA-responsive elements, or ABREs, in promoters and activate genes involved in drought, salinity, and other ABA-mediated stress responses.
3. A plant gene promoter contains a functional ABA-responsive element, or ABRE. Which change would most specifically reduce its induction by ABA?
A.
Mutation of the ABRE core sequence without altering the coding region
B.
Increasing the number of chloroplasts in mesophyll cells
C.
Removing a cell-wall cellulose synthase gene from the genome
D.
Increasing ribosome production in unstressed tissues
Correct Answer:
Mutation of the ABRE core sequence without altering the coding region
Explanation:
ABREs are cis-regulatory DNA sequences recognized by ABA-activated transcription factors. Altering the ABRE can prevent transcription-factor binding and reduce ABA-dependent gene expression.
4. Which comparison correctly distinguishes ABA-dependent and ABA-independent transcriptional responses to dehydration?
A.
ABA-dependent responses commonly involve ABRE-binding factors, whereas ABA-independent responses can involve DREB factors binding DRE/CRT elements
B.
ABA-dependent responses use only DREB factors, whereas ABA-independent responses require ABA receptors
C.
Both responses require direct binding of ABA to every stress-responsive promoter
D.
ABA-independent responses occur only in roots and never involve transcription factors
Correct Answer:
ABA-dependent responses commonly involve ABRE-binding factors, whereas ABA-independent responses can involve DREB factors binding DRE/CRT elements
Explanation:
Stress-responsive genes may be activated through an ABA-dependent pathway involving ABRE and AREB/ABF factors or through an ABA-independent pathway involving DREB transcription factors and DRE/CRT promoter elements.
5. A drought-inducible gene is strongly activated in a mutant lacking ABA biosynthesis but retains an intact DRE/CRT promoter element. Which explanation is most appropriate?
A.
The gene may be regulated through an ABA-independent DREB pathway
B.
The gene must be activated by direct binding of ABA to its coding sequence
C.
The mutation necessarily prevents all dehydration-responsive transcription
D.
The gene can be expressed only after ABA is converted into ethylene
Correct Answer:
The gene may be regulated through an ABA-independent DREB pathway
Explanation:
DRE/CRT elements can mediate dehydration responses through DREB transcription factors without requiring ABA accumulation, so such genes may remain inducible in ABA-deficient plants.
6. Why are late embryogenesis abundant, or LEA, proteins important products of several ABA-induced stress-responsive genes?
A.
They help stabilize cellular proteins and membranes during dehydration
B.
They directly hydrolyze ABA into inactive sugars in the nucleus
C.
They function as ribosomal RNA molecules that increase translation of every gene
D.
They replace DNA polymerase during replication of stressed cells
Correct Answer:
They help stabilize cellular proteins and membranes during dehydration
Explanation:
LEA proteins are commonly induced during ABA-associated dehydration responses and contribute to cellular protection by stabilizing macromolecules and membranes under water-deficit conditions.
7. A constitutively active SnRK2 kinase is introduced into a plant, but the AREB/ABF transcription factors cannot be phosphorylated. Which outcome is most likely?
A.
Reduced activation of many ABRE-controlled stress-responsive genes
B.
Unchanged activation because phosphorylation is unrelated to transcription-factor function
C.
Complete activation of DRE/CRT-controlled genes only through direct ABA binding
D.
Permanent repression of all genes involved in osmotic adjustment
Correct Answer:
Reduced activation of many ABRE-controlled stress-responsive genes
Explanation:
SnRK2 kinases activate AREB/ABF transcription factors by phosphorylation. If phosphorylation cannot occur, expression of many ABRE-regulated stress genes is reduced even when the kinase is active.
8. Which experimental result would provide the strongest evidence that a candidate gene is ABA-responsive at the transcriptional level?
A.
Its transcript abundance increases after ABA treatment, and the increase is reduced when ABA signaling is blocked
B.
Its protein is detected only in chloroplasts of untreated plants
C.
Its DNA sequence contains no promoter or regulatory region
D.
Its transcript remains unchanged after ABA treatment but its amino acid sequence is conserved
Correct Answer:
Its transcript abundance increases after ABA treatment, and the increase is reduced when ABA signaling is blocked
Explanation:
An ABA-dependent increase in transcript abundance, together with loss or reduction of that response when ABA signaling is inhibited, supports transcriptional regulation through the ABA stress-response pathway.
9. Which pairing correctly matches a promoter element with a transcription-factor group involved in stress-responsive gene expression?
A.
ABRE — AREB/ABF
B.
DRE/CRT — ribosomal proteins
C.
ABRE — cellulose synthases
D.
DRE/CRT — plasma-membrane ATPases as DNA-binding factors
Correct Answer:
ABRE — AREB/ABF
Explanation:
AREB/ABF transcription factors recognize ABRE sequences in promoters of many ABA-responsive genes. DRE/CRT elements are instead commonly associated with DREB transcription factors.
10. A researcher observes that a stress-responsive gene is induced by dehydration, but its expression does not increase after exogenous ABA treatment. Which conclusion is most justified?
A.
The gene may belong to an ABA-independent dehydration-response pathway
B.
The gene cannot respond to dehydration because all dehydration responses require ABA
C.
The gene must encode an ABA receptor even though its transcript is ABA-insensitive
D.
The gene is necessarily unrelated to stress because ABA treatment had no effect
Correct Answer:
The gene may belong to an ABA-independent dehydration-response pathway
Explanation:
Dehydration can activate ABA-independent pathways, including those involving DREB transcription factors and DRE/CRT promoter elements. Therefore, lack of response to applied ABA does not exclude dehydration responsiveness.
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