Correct option is C
NPR1’s Role in the Plant Immune System:
- NPR1 plays a central role in the regulation of plant defense mechanisms, particularly in systemic acquired resistance (SAR) and the hypersensitive response (HR).
- Under stress conditions (such as pathogen infection), SA accumulates, which leads to the activation of NPR1.
- NPR1 then accumulates in the nucleus of the plant cells and activates the transcription of PR genes, which are crucial for the SAR response.
Evaluating the Statements:
Statement 1: NPR1 exists as oligomers in the nucleus and activates hypersensitive response.
- This is incorrect. NPR1 exists as monomers in the nucleus, and upon SA activation, it accumulates and binds to other transcription factors to initiate the immune response. Oligomerization is not the key mechanism for activating hypersensitive response.
Statement 2: NPR1 degrades through its binding to NPR3 and leads to activation of SAR response.
- This is incorrect. NPR1 does interact with NPR3, but it does not degrade through this interaction. Instead, NPR1 helps regulate the SAR response through its own activity in the nucleus and binding to other regulatory factors.
Statement 3: NPR1 accumulates in the nucleus and leads to activation of SAR response.
- This is correct. Upon SA binding, NPR1 is stabilized and accumulates in the nucleus. Once in the nucleus, it activates the transcription of genes involved in SAR (systemic acquired resistance), including PR genes. This is the key process through which SAR is mediated.
Statement 4: Binding with NPR4 stabilizes NPR1 in the nucleus, which in turn activates the hypersensitive response.
- This is incorrect. While NPR4 plays a role in the regulation of NPR1, the primary process of hypersensitive response (HR) is not directly linked to NPR1's binding with NPR4. NPR1 is primarily involved in SAR activation, not the initiation of HR.
