Bacterial Leaf Nodule Symbiosis in Flowering Plants

Bacterial leaf nodule symbiosis within angiosperms is a less known phenomenon compared to the well-documented legume root-Rhizobium symbiosis and certainly deserved much more scientific attention. Leaf nodules associated with bacteria was first recognized in Pavetta (Rubiaceae) in early twentieth century. Further survey added other members of Rubiaceae, Primulaceae, Dioscoreaceae, and Styracaceae to the short list of plants with specialized bacteria-containing structure in aerial part of plants. The actual role of the bacteria has been questioned by several researchers, mostly due to the problems associated with the identities of these unculturable bacteria. Many progresses have been achieved provided with molecular phylogenetic analysis and also genomic data of the bacteria. Recent evidence from genomic sequences showed the symbiotic bacteria may serve as a defense role in Primulaceae and Rubiaceae, and may increase stress tolerance in Dioscoreaceae. In this article, we reviewed the current knowledge of the bacterial leaf nodule symbiosis in angiosperm. Future research and applications were also discussed.