A protein phosphatase 2C gene, LjNPP2C1, from Lotus japonicus induced during root nodule development

Symbiotic interactions between legumes and compatible strains of rhizobia r esult in root nodule formation. This new plant organ provides the unique ph ysiological environment required for symbiotic nitrogen fixation by the bac terial endosymbiont and assimilation of this nitrogen by the plant partner. We have isolated two related genes (LjNPP2Cl and LjPP2C2) from the model l egume Lotus japonicus that encode protein phosphatase type 2C (PP2C). Expre ssion of the LjNPP2C1 gene was found to be enhanced specifically in L. japo nicus nodules, whereas the LjPP2C2 gene was expressed at a similar level in nodules and roots. A glutathione S-transferase-LjNPP2C1 fusion protein was shown to have Mg2+- or Mn2+-dependent and okadaic acid-insensitive PP2C ac tivity in vitro. A chimeric construct containing the full-length LjNPP2C1 c DNA, under the control of the Saccharomyces ces cerevisiae alcohol dehydrog enase promoter, was found to be able to complement a yeast PP2C-deficient m utant (pct1 Delta). The transcript level of the LjNPP2C1 gene aas found to increase significantly in mature nodules, and its highest expression level occurred after leghemoglobin (lb) gene induction, a molecular marker for la te developmental events in nodule organogenesis. Expression of the LjNPP2C1 gene was found to be drastically altered in specific L. japonicus lines ca rrying monogenic-recessive mutations in symbiosis-related loci, suggesting that the product of the LjNPP2C1 gene may function at both early and late s tages of nodule development.