Final answer:
In plants, a two-component system regulating gene transcription in response to extracellular signals consists of a sensor kinase that detects the signal and a response regulator that modulates gene expression.
Step-by-step explanation:
In plants, a typical two-component system that regulates gene transcription in response to extracellular signals includes a sensor kinase and a response regulator. The sensor is a membrane-bound protein that detects the environmental signal, while the response regulator is often a transcription factor that enters the nucleus to modify gene expression. This regulatory mechanism is crucial for plants to adapt to changing environments and defend against pathogens.
During biotic stress, such as pathogen attack, plants activate their defense mechanisms utilizing a range of transcription factors, including bZIP, WRKY, and NAC families. These transcription factors, once activated, bind to specific cis-regulatory elements in the promoters of target genes, triggering a cascade of defense gene expressions.
Sensor kinases identify the stress signals and become activated, which then leads to the transfer of a phosphate group to the response regulator. The phosphorylated response regulator can now bind to DNA and regulate transcription. This interaction is part of a larger signaling pathway that is essential for the plant's response to external stimuli.