- A specific Mitogen Activated Protein Kinase (MAPK) cascade comprising MEKK1(a MAP3K), MKK1 (a MAP2K) and MPK6 (a MAPK) is activated sequentially in that order in Arabidopsis plants upon perceiving certain abiotic stress stimuli. The activated MPK6 phosphorylates and activates a transcription factor ‘X’, thereby making plant tolerant to the abiotic stress. Two different variants of MKK I protein, a kinase inactive (KI) and a constitutively active (CA) forms were expressed independently in mkk1 mutant Arabidopsis plant. Considering above facts, which one of the following statements is CORRECT?
(1) ‘X’ will be activated even in the absence of stimuli in CA plants
(2) ‘X’ will not be activated in the absence of stimuli in CA plants
(3) ‘X’ will be activated in the absence of stimuli in KI plants
(4) The KI plants will be tolerant to the abiotic stress.
Correct answer: (1) ‘X’ will be activated even in the absence of stimuli in CA plants
Explanation:
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MEKK1, MKK1, and MPK6 form a MAP kinase cascade that is activated sequentially to respond to abiotic stress.
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MPK6 phosphorylates and activates a transcription factor ‘X’ to enhance stress tolerance.
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Constitutively active (CA) MKK1 means MKK1 is always active, activating downstream MPK6 and transcription factor ‘X’ even in the absence of stress stimuli. This drives continuous stress response activation.
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Kinase inactive (KI) MKK1 cannot phosphorylate downstream targets; hence, no activation of ‘X’ in the absence of stimuli.
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KI plants will not show tolerance to abiotic stress as the signaling pathway is disrupted.
Option-wise:
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(1) Correct; ‘X’ activated in CA plants without stimuli.
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(2) Incorrect; CA is constitutive activation.
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(3) Incorrect; KI is inactive, so no activation.
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(4) Incorrect; KI plants are sensitive due to signaling block.
The MAPK cascade involving MEKK1, MKK1, and MPK6 sequentially activates transcription factor ‘X’ to confer abiotic stress tolerance in Arabidopsis. Constitutively active MKK1 results in ‘X’ activation independent of stimuli, demonstrating how MAPK signaling tightly regulates stress responses for plant survival.
