Which of the following ‘R’ gene products do not contain NBS‐LRR domain?

The correct answer is Option 4 i.e.Mlo protein of barley

Concept:

• Plants rely on two components of their innate immunity system to prevent or treat microbial infections: one responds to pathogen- or microbe-associated molecular patterns using cell surface receptors, and the other uses proteins with nucleotide-binding site (NBS) and Leu-rich repeat (LRR) domains to act inside plant cells.
• Through direct or indirect recognition of pathogen effectors, NBS-LRR proteins promote disease resistance.
• Most of the plant disease-resistance genes (R-genes) cloned so far encode NBS-LRR proteins.

Explanation:

Option 1: RPS2 protein of Arabidopsis

• There are approximately 150 NBS-LRR-encoding genes in Arabidopsis thaliana likeRAC1, RPP5, RPS4, RRS1, RPP8, RPP13, RPS2, RPS5, and RPM1 and N from tobacco.

Option 2: Xa1 protein of rice

• The Xa1 gene in rice confers resistance to Japanese race 1 of Xanthomonas oryzae pv. oryzae, the causal pathogen of bacterial blight (BB).
• Xa1 gene by a map-based cloning strategy deduced amino acid sequence of the Xa1 gene product and was seen to contain nucleotide binding sites (NBS) and a new type of leucine-rich repeats (LRR).

Option 3: N protein of tobacco

• NBS-LRR-encoding genes  N from tobacco is discovered.

Option 4: Mlo protein of barley

• A class of plant integral membrane proteins called the Mlo-related proteins was first identified in barley.
• Mutants lacking wild-type Mlo proteins exhibit dysregulated cell death regulation and spontaneous cell death in response to abiotic or developmental stimuli, as well as broad-spectrum resistance to the powdery mildew fungus, thus option 4 is incorrect and so is the answer.