Involvement of proteases during nodule senescence in leguminous plants

During the plant lifespan, growth, development, and aging is associated with senescence before the final death. However, one of the main purposes of plant tissue senescence is related to an important and vital nutrient remobilization during plant growth. In leguminous plants, the symbiotic association between the plant and the endosymbiont, the Rhizobium, generates the nodule, a new organ formed de novo. In the nitrogen-fixing nodule, senescence is a complex phenomenon directly related to the organ lifespan. The nodule senescence involved specific molecular actors from both partners. The senescence of nodules occurs both during natural aging and under environmental stresses. Mineral nitrogen availability also induces the nodule senescence. This review focuses upon mechanisms associated to the activation of senescence in the two symbiotic partners leading to a programmed cellular degradation and death, with a particular focus on the transcriptional regulation of proteases associated to the transition from nitrogen fixation to cellular degradation.