# DBT JRF 2022 — Question 72

Exam: DBT JRF 2022 · Section: B · Topic: Plant Biology › Nitrogen Fixation - Nod Factors · Difficulty: Medium

## Question

Nod gene products:

## Options

- **A.** function as receptors of certain flavonoids
- **B.** lack the ability to activate the expression of other Nod factors
- **C.** cause activation of homeobox genes
- **D.** are involved in photosynthesis

## Answer

Option A

## Explanation

NodD protein in Rhizobium-legume symbiosis: The Rhizobium-legume symbiosis establishes nitrogen-fixing root nodules: 1. Legume roots secrete flavonoids (e.g., luteolin, naringenin) as chemical signals. 2. NodD protein: a LysR-family transcriptional regulator in Rhizobium that acts as a receptor for plant-secreted flavonoids. When flavonoids bind NodD, it undergoes a conformational change and becomes a TRANSCRIPTIONAL ACTIVATOR. 3. Activated NodD binds to nod boxes (conserved promoter sequences) upstream of other nod genes. 4. Activates expression of NodA, NodB, NodC, etc. → synthesis of Nod factors (lipochitooligosaccharides). 5. Nod factors signal back to the legume root → curling of root hair → infection thread formation → nodule organogenesis. Answer: NodD is a transcriptional activator and flavonoid receptor that activates nod gene expression in Rhizobium.

Source: https://mypyqbuddy.com/questions/nod-gene-products-6a104cd5920734408bc0c757