What are the steps involved in formation of a root nodule?

Explanation

1) Roots of legumes release sugars, amino acids which attracted Rhizobium. They get attached to epidermal and root hair cells of the host.
2) The root hair curl and the bacteria invade the root hair.
3) An infection thread is produced, carrying the bacteria into cortex of the root.
4) Bacteria initiate nodule formation in the cortex of the root. Then the bacteria released from the thread into the cortical cells of the host and stimulate the host cells to divide. Thus leads to the differentiation of specialized nitrogen fixing cells.
5) The nodule thus formed establishes a direct vascular connection with the host for exchange of nutrients.