MSENOD12A EXPRESSION IS LINKED TO MERISTEMATIC ACTIVITY DURING DEVELOPMENT OF INDETERMINATE AND DETERMINATE NODULES AND ROOTS

During development of nodules and roots, the alfalfa early nodulin gen e MsEnod12A is expressed adjacent to the meristem. Using transgenic al falfa carrying a MsEnod12A promoter-gusA fusion, we investigated the r egulation of MsEnod12A expression in mature nodules and roots by GUS a ssays and reverse transcription-PCR. We found that in alfalfa indeterm inate nodules induced by various Fix(-)Rhizobium meliloti mutants and in spontaneous nodules devoid of rhizobia, MsEnod12A was expressed at the distal end when a persistent meristem was present. However, this g ene was not expressed when the meristem was lacking in nodules arreste d in development. The MsEnod12A-gusA fusion was introduced into Lotus corniculatus plants that form determinate nodules devoid of a persiste nt meristem. Using these plants we found MsEnod12A-gusA expression onl y in young nodules and a disappearance in mature nodules. Moreover, wh en alfalfa roots were treated with auxins a lateral band of MsEnod12A expression was observed surrounding the club-shaped root apex and coin ciding with induced lateral meristematic activities. Thus, in all case s MsEnod12A expression was associated with meristematic activities, su ggesting that MsEnod12A plays a role in the differentiation processes of nodule and root cells and that it may serve as molecular tool for a nalyzing meristem establishment during nodule development.