<p>Genes encoding homeodomain leucine zipper, HDZip, transcription factors constitute a large gene family in <i>Arabidopsis thaliana</i>. In this thesis the isolation and characterization of four HDZip genes (<i>ATHB3</i>, -<i>13</i>, -<i>20</i> and -23) is described. These genes are similar in sequence and form a distinct subclass within the HDZip gene family. Since the genes cause similar alterations in cotyledon shape when expressed constitutively, we refer to the members of this subclass as <i>pointed cotyledon</i> HDZip genes. </p><p>To determine the biological functions of the genes, the phenotypes of plants constitutively expressing the genes have been analysed. Each of the genes specifically inhibits lateral cell expansion in cotyledons and leaves and thereby causes them to be abnormally narrow. Detailed expression analysis shows that only <i>ATHB23</i> is expressed in the entire leaf and cotyledon from early stages of development while <i>ATHB20</i> is predominantly expressed in the root cortex. <i>ATHB13</i> is expressed in basal parts of mature leaves and floral organs and <i>ATHB3</i> in root and stem cortex. The ATHB13 protein acts within a signalling pathway that mediates a response to sucrose that specifically regulates the expression of specific sugar-regulated genes. <i>ATHB3</i> specifically inhibits primary root development without affecting the development of secondary roots when constitutively expressed. </p><p>Reduced expression of <i>ATHB3</i> by antisense suppression results in increased expression of <i>ATHB13</i>, indicating that ATHB3 acts as a repressor of <i>ATHB13</i> expression in the wild type.</p><p>This thesis also reports the isolation of seven new genes of HDZip class I and reviews available functional information on the genes in this class. One conclusion is that HDZip I proteins that are closely related phylogenetically are also functionally related, in most cases. Seven different mutations in HDZip I genes were also identified. The lack of phenotypic deviations from wild type of these mutants suggests that these HDZip proteins act in a redundant fashion in the plant.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-1082 |
| Date | January 2000 |
| Creators | Hanson, Johannes |
| Publisher | Uppsala University, Department of Evolutionary Biology, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1104-232X ; 580 |
Page generated in 0.0028 seconds