The Impact Of Blocking Auxin Signalling On The Development Of Arabidopsis Plants

Auxin plays a wide range of regulatory roles in plant growth and development,but many of them have not yet been well characterised,some may not even been discovered.One major factor that hinders our discovery and investigation of auxin's functions in plant development is the limitation of our research methods.Currently most studies in this field rely on the availability of viable mutant plants that are defective in auxin's responses,it is therefore impossible to use this approach to study auxin's functions that are essential for the survival of a plant.In addition,many auxin's regulatory roles involve multiple genes and regulatory pathways,functional redundancy among genes or complex interactions between pathways make some auxin's regulations difficult to detect and investigate.To overcome the above-mentioned limitations,we use a new experimental approach,which explores the fact that mutations within domain II of the Aux/IAA proteins can make them insensitive to auxin-induced degradation and thereby block the relevant auxin signaling pathway and also promoters of tissue specifically expressed genes to generate transgenic plants with induciable and tissue-specific blocking of auxin signalling,and to use them to find and investigate new auxin's functions.The main results of the project includes: 1)introduced specific mutations into the domain II of 22 Aux/IAA proteins(designated as IAAm)and succeeded in making plant expressing constructs of the genes and obtaining transgenic lines;2)compared the effectiveness of different IAAms in blocking auxin signalling in the root apical meristems under the same expression driver J1511 and found that IAA18 m was most effective,its expression in a small number of cells within this organ led to a complete loss of the root apical meristem;3)examined phenotypes in other developmental processes in J1511>>IAA18m-GR plants and found that IAA18 m expresssion led to defects in embryogenesis,shoot apical meristem and floral development,some of which have not been reported previously;4)further characterised the impacts ofIAA18 m expression on root apical meristem,such as time course,dosage effect,and reversibility of the effects of IAA18 m,and find that the impacts were dosage dependent,time accumulating and only reversible if the duration is within 24 hours,becoming non-reversible after 36 hours;5)obtained evidence that auxin signalling in QC cells is critical to the maintenance of the root apical meristem.Blocking auxin signalling specifically in QC could result in division of QC cells,reduced level of expression or disappearance of QC specific markers,upwards shifting and losing control of the surrounding stem cells.The results of the project demonstrate that the experimental strategy of using the expression of domain II mutated Aux/IAA proteins to block auxin signalling pathways is useful not only for discovering new regulatory roles of auxin,but also for studying the details of known auxin regulations,such as the regulatory process,mechanisms and target cells.