Molecular Regulatory Mechanism Of Phosphate Acquisition And Translocation By AtWRKY42 Transcription Factor In Arabidopsis Plants

Phosphorus(P)is an essential nutrient for plant growth and development.In Arabidopsis plants,phosphate(Pi)is absorbed by phosphate transporters,mainly by PHT1;1 and PHT1;4,and is translocated from roots to shoots by PHO1,The expression of PHT1 and PHO1 is regulated accurately to maintain Pi homeostasis in plants.The Arabidopsis WRKY transcription factor family has more than 70 members,and some of them have been reported to play important roles in plant response to biotic and abiotic stresses.The focus of this dissertation work is to characterize the function of AtWRKY42 regulation of phosphate acquisition and translocation in Arabidopsis.WRKY42 protein is localized in the nucleus and can bind to W-box motif.WRKY42 was expressed mainly in roots and repressed during Pi starvation,The WRKY42-overexpressing lines,similar to the phol mutant,were more sensitive to low-inorganic phosphate stress,had higher anthocyanin content,and lower shoot Pi content compared with wild-type plants.The PHO1 expression was repressed in WRKY42-overexpressing lines and slightly enhanced in the wrky42 mutant.ChIP assay showed that WRKY42 protein bound to PHOI promoter under Pi-sufficient condition,and this binding was abrogated during Pi starvation.These data indicate that WRKY42 modulates Pi translocation by down-regulating PHOl expression.Furthermore,under Pi-sufficient condition,overexpression of WRKY42 increased root Pi content and Pi uptake,while the wrky42 mutant had lower root Pi content and Pi uptake rate compared with wild-type plants.Moreover,WRKY42-overexpressing lines were more sensitive to arsenate,an oxyanion structurally analogous to phosphate,compared with wild-type plants.WRKY42 positively regulated PHT1;1 expression by binding to the PHT1;1 promoter,and this binding was abolished by low-Pi stress.Moreover,the interruption of PHT1;1 in WRKY42-overexpressing line(Super:WRKY42/pht1;1)abolished the enhanced Pi uptake of WRKY42-overexpressing line.These data indicate that WRKY42 modulates Pi uptake by up-regulating PHT1;1 expression.During Pi starvation,the binding of WRKY42 to the promoter of PHO1 or PHT1;1 was disrupted,and WRKY42 protein was degraded via the 26S proteasome pathway.In summary,the results presented in this dissertation demonstrates that AtWRKY42 modulates Pi uptake and translocation by directly regulating PHT1;1 and PHO1 expression under Pi-sufficient conditions.During Pi starvation,WRKY42 expression is repressed and the WRKY42 protein is degraded via a proteasome pathway,and then the binding of WRKY42 to the promoter of PHO1 or PHT1;1 is abolished.