Rhizobial lipo-oligosaccharides: answers and questions

Rhizobium bacteria produce certain lipo-oligosaccharides (modified chitin oligomers) after induction of nodulation (nod) gene transcription by the host plant. The function of the rhizobial nod genes in the biosynthesis of these lipo-oligosaccharides, focusing on their host specific aspects, is discussed. The lipo-oligosaccharides can elicit various responses in the host plants, like the formation of pre-infection threads and nodule meristems. Speculating on their function in plant morphogenesis the question is raised: do the rhizobial lipo-oligosaccharides resemble unknown plant signal molecules?