Increased abundance of MTD1 and MTD2 mRNAs in nodules of decapitated Medicago truncatula.

To gain insight into the molecular processes occurring in root nodule metabolism after stress, we used a mRNA differential display (DDRT-PCR) approach to identify cDNAs corresponding to genes whose expression is enhanced in nodules of decapitated Medicago truncatula plants. Two full-length cDNAs of plant origin were isolated (MTD1 and MTD2). Sequence analysis revealed that MTD1 is identical to an EST clone (accession number AW559774) expressed in roots of M. truncatula upon infection with Phytophthora medicaginis, while MTD2 is highly homologous to an Arabidopsis thaliana gene (accession number AL133292) coding for a RNA binding-like protein. The two mRNAs started to accumulate in root nodules at 4 h after plant decapitation and reached even higher transcript levels at 24 h from the imposition of the treatment. MTD1 and MTD2 mRNAs were mainly induced in nodules, with very little induction in roots. The abundance of the two transcripts did not change in response to other perturbations known to decrease nitrogenase activity, such as nitrate and Ar/O2 treatments. Our results suggest that MTD1 and MTD2 represent transcripts that accumulate locally in nodules and may be involved in changes in nodule metabolism in response to decapitation.