Question

Given below are two statements:
Statement (I): Xa21 gene confers resistance to bacterial blight in rice
Statement (II): Xa 21 is a receptor like kinase type of receptor
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

The *Xa21* gene encodes a receptor-like kinase (RLK) that recognizes the bacterial pathogen Xanthomonas oryzae pv. oryzae to trigger immune signaling in rice.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Plants have evolved sophisticated immune receptors to recognize pathogens and trigger defense responses.
These immune receptors are often categorized as pattern recognition receptors (PRRs) or intracellular resistance (R) proteins.

Step 2: Detailed Explanation:
Let us evaluate both statements:
- Statement (I) is correct: The *Xa21* gene was originally identified in and cloned from the wild African rice species Oryza longistaminata.
It has been introgressed into cultivated rice (Oryza sativa) varieties to provide broad-spectrum resistance to Xanthomonas oryzae pv. oryzae, the bacterial pathogen responsible for devastating bacterial blight disease.
- Statement (II) is correct: The *Xa21* gene encodes a well-characterized receptor-like kinase (RLK) protein.
This receptor spans the plasma membrane and contains:
1. An extracellular leucine-rich repeat (LRR) domain that detects the bacterial pathogen-associated molecular pattern (PAMP), specifically the sulfated protein RaxX.
2. A transmembrane domain.
3. An intracellular serine/threonine kinase domain that initiates downstream defense signaling cascades upon ligand binding.
Since both Statement (I) and Statement (II) are correct, Option (A) is the correct choice.

Step 3: Final Answer:
Hence, the correct option is (A).