Cloning And Functional Analysis Of Rice Root Hair Development Related Gene OsEXP17

Root hairs are long tubular outgrowths from epidermal cells of roots.Although many genes regulating root hair development have been isolated in Arabidopsis, knowledge of molecular mechanism of root hair development in monocot cereal crops is largely unclear.In this study,we isolated and further cloned a novel rice short root hair mutant.The main discoveries for the study are as followed.1.A rice mutant with significant short root hair was isolated from an EMS mutant library of Kasalath(indica subspecies).The mutant was named as ksrh1.Genetic analysis showed a recessive nuclear gene controlled the mutant.2.Map-base cloning revealed that there was a point mutant in OsEXP17 (LOC_Os06g01920)on Chromosome 6.And the point mutation results in one of the conserved amino acid residue changed from Gly to Arg. Complementation test confirmed the ksrh1 mutation was caused by the mutation in OsEXP17.The ksrh1 mutant was then renamed as exp17.3.Except shorter and denser root hairs,there were no significant differences in shoots,primary root,adventitious roots and lateral roots,and other agricultural traits of exp17 compared to the wild type(WT),indicating that OsEXP17 specially regulates on the elongation of root hairs.4.Phosphate starvation and exogenous hormones such as NAA(a-naphthaleneacetic acid),6-BA(6-benzylaminopurine)and ACC(1-aminocyclopropane-1-carboxylic acid)induced root hair formation and elongation in the wild type plants.The shorter root hair phenotype in exp17 mutant,however,could be restored partly by application of the above hormones or Pi starvation treatment, implying the OsEXP17 located at downstream signaling steps to regulate root hair initiation and elongation.RT-PCR analysis indicated that OsEXP17 gene was specially expression pattern only in roots.And GUS pattern analyses indicated that OsEXP17 was expressed strongly in root hair cells. Using transient expression of OsEXP17::Subcellular localization of GFP fuse protein,it wass founded that OsEXP17 was a peripheral membrane protein.5.OsEXP17 was ortholog of two Arabidopsis(Arabidopsis thaliana)expansin genes AtEXP7 and AtEXP18.Given that AtEXP7 and AtEXP18 were tightly linked to root hair development and were expressed in the root hair,it appeared that OsEXP17 might be the functional ortholog of AtEXP7 and AtEXP18.Thus,the mechanism of root hair development,at least partly,was conserved between Arabidopsis and rice.In conclusion,we cloned and functionally characterized a rice gene controlling the development of root hair in rice through forward genetic approach.