Correct option is B
Explanation-
SYMRK stands for Symbiosis Receptor-like Kinase. It is a plasma membrane-bound receptor-like kinase (RLK). It plays a crucial role in symbiotic interactions between - Plants and rhizobial bacteria (for nitrogen fixation) and Plants and arbuscular mycorrhizal fungi (for phosphorus uptake).
A typical SYMRK protein has the following domains:
1. Leucine-Rich Repeat (LRR) region - It is located in the extracellular domain and important for ligand recognition (signals from symbionts).
2. Transmembrane domain - It anchors the protein in the plasma membrane.
3. Serine/Threonine kinase domain - It activates downstream signaling after ligand binding.
Incorrect Options-
Option A - Nucleotide binding repeat
It is common in nucleotide-binding leucine-rich repeat (NLR) immune receptors (not SYMRKs). SYMRKs are not primarily nucleotide-binding proteins.
Option C - NAC domain
It is found in NAC transcription factors, involved in development and stress responses, not in receptor kinases.
Option D - W-box
W-box is a DNA motif found in promoters, not in proteins. It is recognized by WRKY transcription factors, not related to SYMRKs.
So ,the correct answer is option B - Leucine-Rich Repeat (LRR) region
