The Rhizobium Strain NGR234 nodD1 Gene Product Responds to Activation by the Simple Phenolic Compounds Vanillin and Isovanillin Present in Wheat Seedling Extracts. Kathryn K. Le Strange. Plant-Microbe Interaction Group, Research School of Biological Sciences, Australian National University, Canberra, ACT, 2601. Gregory L. Bender(1), Michael A. Djordjevic(1), Barry G. Rolfe(1), and John W. Redmond(2). (1)Plant-Microbe Interaction Group, Research School of Biological Sciences, Australian National University, Canberra, ACT, 2601, and (2)School of Chemistry, Macquarie University, North Ryde, NSW, 2109, Australia. MPMI 3:214-220. Accepted 16 January 1990. Copyright 1990 The American Phytopathological Society.

Vanillin and isovanillin are present in extracts of wheat seedlings and interact with the nodulation (nod) gene nodD1 from Rhizobium strain NGR234 to induce expression of R. leguminosarum bv. trifolii nod genes. Seven varieties of Australian wheat were examined. Vanillin, isovanillin, or both were present in five of the varieties tested. Assays of a wide range of authentic flavonoid and other phenolic compounds for transcriptional induction of the same nodA::lacZ fusion revealed that a hydroxyl group para to an electron-withdrawing group and/or the presence of a cluster of oxygen functions are the prime structural requisites for transcriptional activation of NodD1-activated nod genes.