nodABC

nodABC refers to a trio of nodulation genes found in many rhizobia that are essential for the synthesis of Nod factors, the signaling molecules that initiate symbiosis with legume hosts. These genes are typically organized within nodulation gene clusters on plasmids or symbiotic elements and are conserved across diverse rhizobial species.

NodA, NodB, and NodC encode enzymes that build the core Nod factor structure. NodC is a glycosyltransferase that polymerizes N-acetylglucosamine into the chitooligosaccharide backbone of the Nod factor. NodB is a chitin deacetylase that modifies the backbone by deacetylating the reducing end, contributing to the final chemical form. NodA is an acyltransferase that attaches a fatty acyl tail to the Nod factor, generating the lipid-modified signal that facilitates recognition by plant receptors.

The resulting Nod factors are lipo-chito-oligosaccharides (LCOs) whose backbone length, acetylation status, and lipid modifications influence host range and nodulation efficiency. While the core scaffold produced by NodABC is conserved, additional nod genes add specific decorations that customize signals for particular legume species, thereby affecting compatibility and specificity of the symbiotic interaction.

Regulation of nodABC expression typically involves plant-derived flavonoids that activate transcription through the NodD regulator. This regulatory mechanism links Nod factor production to the presence of suitable host plants, ensuring energy is spent on signaling only when a compatible legume partner is available.

NodABC is widely studied for its central role in rhizobial nodulation programs. Variations in these genes contribute to differences in Nod factor structure and, consequently, to the effectiveness and range of legume symbioses.