Final answer:
The ethylene signaling pathway activates AP2/ERF transcription factors by relieving inhibition, which in turn increases expression of genes essential for plant defenses and development.
Step-by-step explanation:
The ethylene signaling pathway is crucial for various plant processes, including gene regulation. When ethylene binds to its receptor, it initiates a cascade of events that lead to the activation of AP2/ERF transcription factors. These transcription factors are normally kept inactive by interacting with inhibitors like EIN2. Once activated by ethylene, they are released from these inhibitors and translocate to the nucleus, where they bind to specific DNA sequences called GCC-box or other cis-elements in promoter regions of target genes, thereby initiating transcription.
Various proteins interact with AP2/ERF transcription factors to modulate their activity. For instance, factors like AtEBP can bind to OBF, enhancing the transcription of pathogenesis-related (PR) genes. Additionally, phosphorylation and dissociation events can modify AP2/ERF proteins, either increasing their activity, as seen with the proteins ORC1 after phosphorylation, or facilitating their nuclear translocation, as with the dissociation of EREBP from NLP proteins after ethylene induction. As a result, there is increased expression of PR genes, helping the plant to withstand biotic stress.