Scientists have identified two putative plant transcription factors that are essential links in the symbiosis of rhizobial bacteria and legumes, according to two reports in this week's Science. The transcription factors–GRAS family proteins NSP1 and NSP2–may play distinct yet cooperative roles in regulating the development of nodules on the plant roots where the nitrogen-fixing bacteria reside.

"The interesting aspect of this is that we have a couple of GRAS proteins here that are fairly well positioned in the signaling pathway with clear phenotypic effects," Michael Udvardi, of the Max Planck Institute of Molecular Plant Physiology, Golm, Germany, and coauthor of a Perspective accompanying the studies, told The Scientist.

Legumes initiate the symbiotic relationship between bacteria and plant by emitting flavonoid compounds that are recognized by the bacteria. Rhizobia then produce Nod factors, oligosaccharides that elicit dramatic alterations in the gene expression and metabolism of both...

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