Study Of The Molecular Mechanism For Arabidopsis Transcription Factor AtYY1 To Regulate Root Development

Plant zinc finger proteins constitute one of the largest transcription factor families,and function in the regulation of plant growth,development,and stress adaptation.Arabidopsis thaliana genome contains 176 zinc finger proteins,one of which is Arabidopsis YIN YANG(AtYY1)zinc finger transcription factor.It has been reported that AtYY1 has its expression induced by abscisic acid(ABA)and salt-stress,and regulates Arabidopsis response to abiotic stress such as drought.AtYY1 loss of function mutant yy1 has been found to have an enhanced drought resistance via ABA-induced stomatal closing.Plant drought resistance requires strong root system to provide water and nutrients.AtYY1 mutation may alter Arabidopsis root system and enable yy1 mutants to acquire enhanced drought resistance trait.UV-B is an important stress to plant growth and development,and has been found to inhibit plant root development.Consequently,it would be interesting and necessary to study whether UV-B could affect AtYY1 expression and function to control Arabidopsis root development,and investigate whether AtYY1 could modify UV-B effect on Arabidopsis.Therefore,the purpose of this thesis is to determine whether AtYY1 mutation affect Arabidopsis root development and response to UVB stress,and subsequently study the molecular mechanism for AtYY1 to regulate root development and UV-B response.In this thesis,two T-DNA insertion mutants of AtYY1,yy1-1 and yy1-2 were identified to have extremely low AtYY1 expression.Molecular and genetic analysis of AtYY1 loss of function mutation in this thesis has gotten the following five novel findings.1.AtYY1 functions to control Arabidopsis lateral root(LR)development through regulation of auxin accumulation in roots.yy1-1 and yy1-2 produced significantly more LR than Col-0.The findings show that auxin,rather than ABA,could rescue yy1-2 LR phenotype and yy1-2 accumulated more auxin in root tips and developing lateral root primordium(LRP)indicate auxin’s function in AtYY1 regulated LR development is to control LR initiation.2.AtYY1 directly binds to YUCCA 6(YUC6)promoter to downregulate YUC6 expression and repress LR development.YUC6 expression was significantly increased in yy1-2 as compared with Col-0,indicating that AtYY1 represses YUC6 expression in Arabidopsis roots.Molecular and genetic analysis of yy1-2 and yuc6 found that AtYY1 and YUC6 function in the same pathway to control LR development.In this pathway,AtYY1 downregulates YUC6 expression by directly binding to YUC6 promoter region III where H3K27me3 is reduced.3.AtYY1 and CURLY LEAF(CLF)have additive effect in regulating LR development through physical interaction.yy1-2 and clf-28 seedlings produced more LR than did Col-0,the double mutant yy1-2 clf-28 seedlings generated significantly more LR than did the single mutants,indicating yy1-2 and clf-28 have additive effect to increase LR number,and AtYY1 and CLF enhance each other’s function in regulating LR development.Yeast two hybrid and Bi FC assays demonstrate that AtYY1 could interact with CLF.And RNA seq data suggest that AtYY1 and CLF may share a common downstream pathway and genes to regulate LR development.4.AtYY1 functions to control Arabidopsis de novo root regeneration(DNRR)capacity and downregulates SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 10(SPL10)expression by directly binding to SPL10 promoter.The leaf explants of yy1-2 had much lower capacity to produce adventitious roots than did Col-0 leaf explants.Auxin could rescue yy1-2’s low DNRR capacity,while reducing ABA in yy1-2 enhanced DNRR capacity.Therefore,auxin and ABA are involved in AtYY1’s function to control Arabidopsis DNRR capacity.SPL10 was a repressor of root regeneration.Ch IP-q PCR and EMSA analysis found that AtYY1 could directly bind to SPL10 promoter to downregulate SPL10 expression.5.AtYY1 has its expression upregulated by UV-B radiation and regulates Arabidopsis response to UV-B stress in LR development,stomatal closure and ’abiotic stress memory’.First,UV-B dramatically increased AtYY1 expression as compared with normal light and rescued yy1-2 LR phenotype,indicating UV-B could upregulate AtYY1 expression to repress LR development.Second,yy1-2 stomatal aperture was reduced significantly more by UVB than that in Col-0 and two AtYY1 overexpression lines.Therefore,AtYY1 may function to mitigate UV-B’s function to reduce stomatal aperture.Third,treating yy1-2 and Col-0 in a UV-B priming system found yy1-2 and Col-0 had UV-B primed ’abiotic stress memory’,but yy1-2 is less sensitive to UV-B primed ’abiotic stress memory’ than Col-0,indicating that AtYY1 is required for UV-B primed ’abiotic stress memory’.