Roles Of SAUR5 In ABA And Auxin Signaling

Abscisic Acid(ABA)regulates multiple aspects of plant growth and development.Most importantly,ABA is involved in the regulation of plant responses to environmental stresses.Auxin is the first identified plant hormone,which plays an important role in the regulation of morphogenesis and tropic responses.Results from some studies have shown that cross-talk between auxin and ABA regulates several aspects of plant growth and development such as seed germination and root elongation.Small Auxin-up RNAs(SAURs)are a family of Auxin response genes that has been found in dozens of species,with a total number of 674.Currently,the reports on the functions of SAURs are mainly focused on the regulation of plant morphologenesis and auxin signaling.In the process of identification and characterization of the ABA response gene in Arabidopsis,we found that the expression level of AtSAUR5 a SAUR gene was significantly reduced upon ABA treatment.To characterize the founctions of AtSAUR5 in plant growth and development,we first cloned AtSAUR5 into different expression vectors for protoplast transfection assays and to generate transgenic plants overexpressing AtSAUR5.We found that AtSAUR5 was located in the nucleus and repressed reporter gene expression in protoplast transfection assays,we also found that both ABA and auxin affected their transcriptional repression on the repoeter gene.Green seedling analysis results showed that sensitivity to ABA was increased transgenic plants overexpressing AtSAUR5,but remained largely unchanged in the atsaur5 mutants when compared to that in wild type.Root elongation assays showed that both AtSAUR5 transgenic plants and atsaur5 mutant seedlings sowed a wild type response to ABA.Water loss assyas showed that both AtSAUR5 transgenic plants and atsaur5 mutants loss water significantly slower when compared with that in Col wild type plants.Consistant with this,stomatal aperture in AtSAUR5 transgenic plants and atsaur5 mutant was smaller than that in Col wild-type plants.Hypocotyl elongation assays indicated that auxin sensitive in both AtSAUR5 transgenic plants and atsaur5 mutants was reduced.However,no changed in auxin was observed in AtSAUR5 transgenic plants and atsaur5 mutants root elongation assays.In summary,our results showed that the expression of AtSAUR5 is inhibited by ABA and induced by auxin.AtSAUR5 is located in the nucleus,has transcriptional repression activity,and is involved in the regulation of plant reponsese to auxin and ABA.Information provided by this study may be of help for further functional characterization of the AtSAUR5 function,and for exploring the cross-talk between ABA and auxin signling.