Dissecting Symbiosis: Developments in Nod Factor Signal Transduction

Identification and Characterization of Nodulation-Signaling Pathway 2, a Gene of Medicago truncatula Involved in Nod Factor Signaling

“…The site of fixation is the nodule, a unique plant organ located on the root, which functions to generate the aerobic environment essential for bacterial survival and nitrogenase activity. Nodule formation involves plant/ bacterial signaling, with the bacterially generated signaling molecule Nod factor playing a critical role (Long, 1996;Downie and Walker, 1999;Oldroyd, 2001).Purified Nod factor, when applied to the appropriate plant host, can induce many of the plant responses associated with exposure to the bacterial symbiont (Downie and Walker, 1999). Nod factors act predominantly on two cell types in the root: epidermal cells and inner cortical cells.…”

“…Nod factor also induces mitotic activation of inner cortical cells that ultimately leads to the development of the nodule primordia. The formation of infection threads, that allow the invasion of bacteria into the root cortex, involves Nod factor, but also requires the presence of the rhizobial bacteria, suggesting the possible role of additional bacterial-signaling molecules (Dé-narié et al, 1996;Oldroyd, 2001).Genetic dissection of the Nod factor-signaling pathway has been limited by the availability of a genetically tractable legume system. Medicago truncatula and its symbiotic bacterial partner Sinorhizobium meliloti have been adopted as model organisms for the study of this symbiotic interaction (Cook, 1999).…”

“…The site of fixation is the nodule, a unique plant organ located on the root, which functions to generate the aerobic environment essential for bacterial survival and nitrogenase activity. Nodule formation involves plant/ bacterial signaling, with the bacterially generated signaling molecule Nod factor playing a critical role (Long, 1996;Downie and Walker, 1999;Oldroyd, 2001).…”

“…Nod factor also induces mitotic activation of inner cortical cells that ultimately leads to the development of the nodule primordia. The formation of infection threads, that allow the invasion of bacteria into the root cortex, involves Nod factor, but also requires the presence of the rhizobial bacteria, suggesting the possible role of additional bacterial-signaling molecules (Dé-narié et al, 1996;Oldroyd, 2001).…”

Peace Talks and Trade Deals. Keys to Long-Term Harmony in Legume-Microbe Symbioses

“…Bacteria are released from the infection thread into membrane bound compartments, where they differentiate into bacteroids. Nod factors, or lipo-chito-oligosaccharide signaling molecules, are central to the initial establishment of the legume-rhizobial symbiosis (Dénarié et al, 1996;Long, 1996;Oldroyd, 2001). Production of this signaling molecule is activated by the release of plant phenolic signals, predominantly flavonoids, into the rhizosphere, where they activate Nod factor production through induction of a set of nod genes in the appropriate rhizobial strain.…”