|DEL GRECO, A|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/23/2000
Publication Date: N/A
Technical Abstract: At least three different sets of symbiotic signals are exchanged between legumes and rhizobia during nodule development. Flavonoids, the first of these, emanate from the plant and interact with rhizobial NodD proteins that serve both as environmental sensors and activators of nod-gene transcription. NodD-flavonoid complexes activate transcription from defined nod-box promoters. Most of the genes immediately downstream are involved in the synthesis of lipo-oligosaccharidic Nod-factors that provoke deformation of the root-hairs and allow rhizobia to enter the root through infection threads. Fine-tuning of nod-gene transcription is probably due to sequence variations in individual nod-boxes (the symbiotic plasmid of the broad host-range Rhizobium sp. NGR234 has 19 of them). Other rhizobial products are necessary for continued infection thread development. Amongst these are extra-cellular polysaccharides (EPS) and related compounds, as well as proteins exported by the type three secretion system. In the latter case, flavonoids also activate protein secretion, suggesting that the same keys can unlock different doors.