Arabidopsis leaf mutants reveal conserved and unique proteins involved in light and auxin signaling

Growth and development in plants is steered by the meristems which are established on both poles of the embryo and become active after germination. The activity of the shoot apical meristem (SAM) leads to the formation of lateral organs such as leaves which are responsible for photosynthesis. At flowering time the SAM is transformed to the inflorescence meristem which produces flowers as lateral organs. The root apical meristem is responsible for the growth of the primary root and is important in water- and mineral-uptake. Within the research group “Chromatin and Growth Control” several genes are being cloned of which the mutant phenotype shows a defect in leaf growth. This way the genes coding for components of the Elongator complex were identified. In yeast Elongator was defined as a histone acetyltransferase (HAT) complex associated with RNA polymerase II to facilitate transcription elongation. In this thesis the loci of two other leaf mutants ang3 and ron3 belonging to the angusta and rotunda class respectively were cloned. By transcript profiling of the leaf mutants using micro-array data we try to pinpoint in which biological process the gene is involved. Localization studies and tandem affinity purification of the respective protein helps to identify which molecular pathways are likely to be affected. With detailed phenotypical analysis of the mutants we are often able to link the affected processes to observed phenotypes. Depending on the obtained results we perform specific experiments (ChIP, hormone measurements,…) to verify the true function of the protein. This work aimed at investigating the role of the Elongator complex in plants and several objectives were put forward 1. To prove the role of Elongator in transcription 2. To identify target genes of Elongator using chromatin-immuno-precipitation Besides the functional characterization of the Elongator complex, two other leaf mutants ang3 and ron3 belonging to the angusta and rotunda class respectively were cloned and functionally characterized. The genes were cloned by fine-mapping combined with sequence analysis of candidate genes in the genetic interval around the locus of interest. Molecular analysis of the genes was combined with morphological and cellular analyses of the corresponding mutants to determine the cellular basis of the observed growth defects and to gain deeper insight into the function of the genes