THE MEDICAGO-TRUNCATULA MTANN1 GENE ENCODING AN ANNEXIN IS INDUCED BYNOD FACTORS AND DURING THE SYMBIOTIC INTERACTION WITH RHIZOBIUM-MELILOTI

Here we report the characterization of a new Nod factor-induced gene f rom Medicago truncatula identified by mRNA differential display. This gene, designated MtAnn1, encodes a protein homologous to the annexin f amily of calcium- and phospholipid-binding proteins. We further show t hat the MtAnn1 gene is also induced during symbiotic associations with Rhizobium meliloti, both at early stages in bacterial-inoculated root s and in nodule structures. By in situ hybridization, we demonstrate t hat MtAnn1 expression in nodules is mainly associated with the distal region of invasion zone II not containing infection threads, revealing MtAnn1 as a new marker gene of the pre-infection zone. Moreover, anal yses of MtAnn1 expression in response to bacterial symbiotic mutants s uggest that the expression of MtAnn1 during nodulation requires biolog ically active Nod factors and is independent of the infection process.