Engineering The Nodulation Signaling Pathway In Rice Plant

Rice is the 2^nd most produced cereal in the world but is most consumed staple food. As the population is increasing, it is estimated that we need to increase the rice yield by about 60% more over the current level, to meet growing demand for food. Nitrogen is an important nutrient for rice production, and its requirement is estimated to increase by 50% by 2050 to boost the rice yields. With the advent of Green Revolution, chemical fertilizer has become the main source of nitrogen supply for rice cultivation, and the production of the synthetic fertilizers uses non-renewable resources. Because of the increased environmental concerns due to the use of synthetic N fertilizers, researchers worldwide are now seriously considering alternative sources of N for crop production in order to meet the increasing demand in coming years. Biological nitrogen fixation (BNF) is a potentially attractive alternative source for nitrogen for crop production. Legumes derive nitrogen for their growth by forming symbiosis with nitrogen-fixing rhizobia. In fact, legumes form symbiotic association with endomycorrhizal fungi as well as rhizobia, the formation of which is mediated by a conserved genetic network termed as common symbiosis pathway, CSP serves as a shared common genetic framework for the development of both types of root symbioses in legumes. On the other hand, rice is able to form symbiotic association only with endomycorrhizal fungi; however, most importantly its development is also mediated by the same set of genetic elements of CSP. These findings implied that a part of the genetic network which supports rhizobial symbiosis in legumes is also conserved in rice, and it could form building blocks to add-on legume-specific symbiotic genetic networks to construct a rice plant responsive to rhizobial association. Some of the crucial genes which are essential for the initial signal transduction to promote rhizobial symbiosis are not well conserved in rice. Thus we have developed transgenic rice lines expressing legume nodulation-specific receptor kinase (LYK3 and NFP) and transcription factor (NSP1, NSP2 and NIN) genes, and assessed their ability promote symbiotic responses towards rhizobial inoculation. In the current presentation, responses of rice roots towards rhizobial symbiotic-cues will be discussed.