INHIBITION OF THE EXPRESSION OF BRADYRHIZOBIUM-JAPONICUM NOD GENES ATLOW-TEMPERATURES

The effect of temperature on the induction of nod gene expression in B radyrhizobium japonicum by the isoflavone genistein was investigated. Experiments were conducted to examine the expression of a nodY-lacZ fu sion of B. japonicum USDA110 under suboptimal incubation temperatures. The results of these studies indicated that higher genistein concentr ations were required for maximum amounts of nodY-lacZ induction at 10 and 15 degrees C than at 25 degrees C. In addition, the time required to achieve maximal amounts of expression was significantly longer at t he suboptimal temperatures. The effects of temperature on nod gene exp ression correlate with previously described inhibition of soybean nodu lation that occurs at low root zone temperatures. The findings reporte d here indicate that this nodulation inhibition is in large part due t o temperature effects on nod gene induction. (C) 1997 Published by Els evier Science Ltd.