Cloning And Functional Analysis Of OsRGA Controlling Root Development In Rice (Oryza Sativa)

Fibrous root system (most of the monocots) are composed of primary root, numerous adventitious roots (AR, also called crown roots or shoot-born roots) and lateral roots on it. Compared with the tremendous research progress on root development in eudicots model plant Arabidopsis (Arabidopsis thaliana L.), the knowledge on molecule mechanism of AR development is still little.In this study, we isolated a rice mutant with defects in both lateral and adventitious root development with a temperature region. Under constant growth temperature of 30℃, the mutant seedling showed lateral rootless and adventitious rootless at its early growth stage, and a few lateral and adventitious roots would emerge at late stage. Further phenotypic analysis showed that the root development of the mutant could be recovered to some extent, under either higher or lower growth temperature.By map-based cloning, the mutation gene was mapped on Chr 4 between marker dCAPS04g657K and STS04g700K. Sequencing analysis indicated that a point mutation occurred in a gene coding disease resistance protein RGA3 (R gene, LOC_Os04g02110), resulting in valine-to-alanine change in the NBS (nucleotide binding site) domain of the R gene product. So the mutant was named Osrga (resistance gene analoge). Overexpression of OsRGA in the Ostrga mutant can rescue the defects of adventitious root and lateral roots.Bioinformatic analysis showed that OsRGA belong to the CC (coiled-coil)-NBS-LRR (leucine rich repeat) subfamily of the R gene superfamily. Moreover, the OsRGA homologs were found existence in the eudicot Ricinus communis L. and the monocot Musa acuminata L., and all of them share similar conserved domains. It indicates that the CC-NBS-LRR subfamily of plant R genes are evolutionarily conserved between the eudicots and the monocots. OsRGA is predictly localized in the cytoplasm.Previous studies showed that many R gene family members in rice were involved in plant disease resistance, while little result has been reported to connect R gene with root development. Analysis of the expression patterns of OsRGA in various tissues showed that it was expressed both in the underground tissues (roots and root-base) and the upground tissue. The expression patterns are different under different temperatures region,which impliciting that OsRGA is thermoregulated.