Localization of the MADS domain transcriptional factor NMH7 during seed, seedling and nodule development of Medicago sativa

The NMH7 gene encodes a possible MADS-domain transcription factor expressed in the nodules and flowers of Medicago sativa. In this study we characterized NMH7 expression at different stages of M. sativa development and in nodules. RT-PCR and western blot analyses revealed that NMH7 is expressed in seeds, cotyledon seedlings, and primary roots. Examination of seedlings grown under different light conditions revealed that NMH7 gene expression is not regulated by phytochrome. In seeds, NMH7 was immunolocalized in the shoot and radicle embryonic meristems, and in parenchyma cells. No signal was detected in the procambium or radicle central cylinder, however. In seedlings, the NMH7 protein was specifically localized in the cortex parenchyma of the root tip and in the root elongation zone. The localization of NMH7 is coincident with the previously reported mRNA pattern, except for the localization of NMH7 in the nodule inner cortex first cell layer. This may be due to protein movement between cells via plasmodesmata. The presence of NMH7 prior to bacteria inoculation suggests that this protein is involved in non-symbiotic events or that NMH7 is involved in nodule developmental programs related to bacteria colonization.