Correct option is A
The correct answer is (a).
The cytokinin and ethylene signaling pathways in plants are evolutionarily related to bacterial two-component regulatory systems. Both cytokinin and ethylene signaling mechanisms utilize receptor kinases that detect environmental or internal signals, which is a feature shared with bacterial two-component systems. In this system, the receptor kinases are similar to those in bacteria, where they activate response regulators to mediate downstream effects, facilitating plant growth and responses to environmental stimuli.
Incorrect options-
Option (b) Brassinosteroid and auxin: These hormones use different receptor systems; brassinosteroids signal via receptor-like kinases, and auxin uses ubiquitin-mediated proteolysis. Neither is related to two-component systems.
Option (c) Auxin and cytokinin: Although cytokinin signaling is two-component related , auxin signaling is not, making this option incorrect.
Option (d) Brassinosteroid and strigolactone: Both use distinct receptor systems unrelated to two-component signaling pathways.
