Rhizobium Nod Metabolites and Early Nodulin Gene Expression

Abstract

The Rhizobium-legume interaction results in the formation of a new plant organ, the root nodule, in which the bacteria are able to reduce atmospheric N2. These root nodules have a very distinctive tissue organization, which allows the N2 fixation process to occur [1]. In short the Rhizobium-legume interaction involves the following steps: It starts with the deformation and curling of root hairs. The rhizobia then invade the plant by means of a newly formed tube, called the infection thread. Meanwhile, cells in the root cortex start to divide and form the nodule primordium. Infection threads enter individual primordium cells, and bacteria are relased form the infection thread into the cytoplasm of the plant cells. The primordium cells then differentiate into the tissues that make up the mature nodule. Rhizobium thus induces three distinct developmental processes in its host (i) root hair deformation, (ii) infection thread formation, and (iii) induction of cell division followed by differentiation into the different nodule tissues.