EXPRESSION OF EARLY NODULIN GENES IN ALFALFA MYCORRHIZAE INDICATES THAT SIGNAL-TRANSDUCTION PATHWAYS USED IN FORMING ARBUSCULAR MYCORRHIZAEAND RHIZOBIUM-INDUCED NODULES MAY BE CONSERVED

Transcripts for two genes expressed early in alfalfa nodule developmen t (MsENOD40 and MsENOD2) are found in mycorrhizal roots, but not in no ncolonized roots or in roots infected with the fungal pathogen Rhizoct onia solani. These same two early nodulin genes are expressed in unino culated roots upon application of the cytokinin 6-benzylaminopurine, C orrelated with the expression of the two early nodulin genes, we found that mycorrhizal roots contain higher levels of trans-zeatin riboside than nonmycorrhizal roots. These data suggest that there may be conse rvation of signal transduction pathways between the two symbioses-nitr ogen fixing nodules and phosphate-acquiring mycorrhizae.