Molecular analysis of plant architecture in Arabidopsis thaliana using activation tagging.

Keywords: Arabidopsisthaliana, activation tagging, T-DNA, transposon, mutants, enhancer, DNA methylation, plant architecture, development, forward/reverse genetics, lateral organs, flower, vascular tissue, HLH, transmembrane, transcription factors<o:p></o:p></span>Plant development is one of the most important aspects of plant's life cycle that has extensively been studied at the morphological, genetic and molecular level. It is import for systematic and taxonomic classification, but also for applied agronomic reasons, because it affects the growth and cultivation leading to higher yield and quality of the product.<span class=GramE>The generation of genetic variants, like mutants may increase genetic pool and gives information about plant processes and their genetic control.</span>Activation tagging is a new powerful tool to generate and identify new mutants, which emerged as an alternative for gene function analysis. This thesis reports the study on the molecular control of plant architecture, using mutants generated by an activation tagging-based approach in the model plant Arabidopsis thaliana . In addition, it also describes experiments that could explain why the low frequencies of mutants were obtained by T-DNA based activation tagging. Based on this comparison, the transposon-based activation tagging strategy was chosen and a screen for flower and silique mutants in a large Arabidopsis population yielded three gain-of-function mutants. These mutants were designated downwards siliques1 ( ds1-D ), needle1 ( ndl1-D ) and twisted1 ( twt1-D ). In the ds1-D mutant, internodes are shorter and the lateral organs such as flowers are bending downwards. Further molecular and genetic studies on this mutant revealed that DS1 is important to control petiole-blade boundary in Arabidopsis petals. In the ndl1-D mutant, the normal formation of valve tissues is altered, resulting in a pin-like structure that replaces the two fused carpels of the wild type pistil. The results suggest that NDL1 is involved in normal carpel development, in which auxin distribution plays an important role. In the third mutant, twt1-D , the overexpression of TWT1 led to twisting of all organs, which<span class=GramE>is</span>most pronounced in siliques. This phenotype and the expression pattern of the gene suggest that TWT1 is involved in proper vascular tissue development in Arabidopsis . These studies demonstrate the power of activation tagging and it gains valuable knowledge about the molecular networks that control plant development