Induction of Genes Encoding Phenylpropanoid Biosynthetic Enzymes in Soybean Roots Inoculated with B. japonicum, Requires Nod Gene Induction and Occurs Independent of Any Known Host Functions

Abstract

To address the possible roles of phenylpropanoid compounds in events occurring in roots following inoculation with the compatible symbiont, we have monitored expression of the gene members encoding phenylalanine ammonia lyase (PAL), chalcone synthase (CHS) and chalcone isomerase (CHI) during nodule development in soybeans. Plant and bacterial mutants that arrest nodule development at defined stages were analyzed to correlate changes in expression of PAL, CHS and CHI genes with distinct events in nodule development. Our results suggest that induction of the ‘symbiosis specific’ PAL and CHS gene members occurs prior to any known host responses like root hair curling, infection thread formation and cortical cell proliferation. Furthermore, our results show a direct correlation in the level of PAL and CHS transcripts with the number of successful nodule foci suggesting that the resulting phenylpropanoid compounds may play a role in cortical cell proliferation associated with nodule development.