Cloning And Functional Analysis Of OsRHL1 Controlling Root Hair Development In Rice (Oryza Sativa)

Root hairs are long tubular outgrowths that form on the surface of specialized epidermal cells.The process of root hair formation in Arabidopsis(Arabidopsis thaliana) has been explored extensively,however little information is available about the genetic and molecular basis of root hair development in monocots.Here,we have cloned a basic/helix-loop-helix(bHLH) gene,designated as OsRHL1(Root Hairless1), which controls root hair elongation in rice(Oryza sativa).In two Osrhl1 allelic mutants,root hair development was initiated normally,while the root hair tip growth was impaired.Overexpression of OsRHL1 in rice and Arabidopsis results in longer root hairs.RT-PCR analysis and transgenic plants of OsRHL1 promoter-GUS indicate that OsRHL1 is expressed in root elongation zone,root hairs,hull,base of panicle and panicle neck hairs,but not in leaf,stem and flower.A green fluorescent protein(GFP) fusion of OsRHL1 driven by the OsRHL1 promoter complemented the root hair phenotype of Osrhl1 mutant,OsRHL1-GFP localized in nuclei of some epidermal cells of root elongation zone and root hairs.These results suggest that OsRHL1 is a key regulator to promote tip growth of root hairs in rice.OsRHL1 belongs to the subfamily C of rice bHLH family,and is highly homologous to members of the subfamily XI of bHLH family in Arabidopsis.Three members of subfamily XI act in a partially redundant manner to regulate root hair elongation in Arabidopsis.The homology gene of OsRHL1 in Lotus japonicus LjRHL1 was also shown to play a important role in root hair elongation.Thus,the mechanism of root hair elongation may be conserved in eudicots and monocots.