Symbiosis
The symbiosis between S. meliloti and its plant hosts begins when the plant secretes an array of betaines and flavonoids into the rhizosphere: 4,4′-dihydroxy-2′-methoxychalcone, chrysoeriol, cynaroside, 4′,7-dihydroxyflavone, 6′′-O-malonylononin, liquiritigenin, luteolin, 3′,5-dimethoxyluteolin, 5-methoxyluteolin, medicarpin, stachydrine, and trigonelline. These compounds attract S. meliloti to the surface of the root hairs of the plant where the bacteria begin secreting nod factor.
Read more about this topic: Sinorhizobium Meliloti