Molecular genetics of rice root development

Plant roots have a large range of functions, including acquisition of water and nutrients, as well as structural support. Dissecting the genetic and molecular mechanisms controlling rice root development is critical for the development of new rice ideotypes that are better adapted to adverse conditions and for the production of sustainably achieved rice yield potential. Most knowledge regarding the gene networks involved in root development has been accumulated in the model dicotyledon plant species Arabidopsis thaliana. Rice, the model monocotyledon species, presents several singularities compared to A. thaliana, including a root architecture characterized by a fibrous root system comprising five types of embryonic and postembryonic roots. The anatomy and morphology of the rice root system, which is typical for a cereal, differs from that of A. thaliana, for instance, by the presence of a lysigenous cortex and additional cell layers compared to the dicotyledon model. Moreover, the structure and functions of the root apical meristem (RAM) of rice are distinct from those of A. thaliana. Recently, several rice root mutants have been identified via forward or reverse genetics, and these will aid in forming hypothesis to characterize either the divergence or conservation of genetic pathways relative to A. thaliana. Furthermore, these mutants will help to identify key genes in rice roots that may be missing in A. thaliana. This review summarizes both classical and recent data concerning the molecular genetics of rice root development, including root anatomy and morphology, RAM structure, RAM patterning, and root mutant