The role of MONOPTEROS and other auxin response factors in root secondary development

With the aggravation of global environmental problems and the reduction of finite reserved fossil fuels, seeking for alternative energy sources has become one of the priorities for the sustainable development of human society. Vascular plants save the biomass mainly as the form of xylem (also called as wood), which is now considered as an ideal environmental-friendly energy resource. Wood is now being used as renewable biofuels, Biomass composites to replace plastic and so on. The lateral meristem vascular cambium gives rise to xylem and phloem, contributes to the radial growth of plants. Dr. Mähönen’s group choose Arabidopsis root as a model to understand the growth dynamics of vascular cambium. Auxin is essential for various plant developmental processes. The transcription factor family AUXIN RESPONSE FACTOR (ARF) is an important component in auxin signaling pathway, among which AUXIN RESPONSE FACTOR5 (ARF5)/MONOPTEROS (MP) has been discovered to be essential in various plant developmental processes. The first part of my thesis work mainly focuses on analyzing the expression of ARFs during Arabidopsis root secondary development by using both histological reporter GUS and green fluorescent protein GFP. The second part is screening the secondary growth phenotype among the arf knock out mutants. As mp mutant fails to form primary root, artificial microRNA technique is applied to inhibit MP expression in transcriptional level, this construct was established in an XVE inducible system and driven by a broadly expressed promoter to specifically inhibit MP expression at the secondary development stage. I overexpressed amiMP in both wild type background and arf7,19 double mutant background. These three ARFs have strong expressions in cambium and they might function redundantly to regulate cambium activity. Our preliminary results suggest that ARFs function redundantly in regulating root secondary growth, ARF1 and ARF2 together are functional in regulating vascular pattern formation, and ARF16 can repress the root secondary growth and secondary xylem formation. MP is proved to regulate cambium activity and secondary xylem formation by controlling various auxin-response genes, ARF7 and ARF19 might also participate in this process