The role of KANLIKE1 and KANLIKE2 genes in leaf development

Abstract

In Arabidopsis thaliana, the Class III HOMEODOMAIN LEUCINE ZIPPER (HD-ZIP III) genes play a crucial role in regulating leaf flatness. Recently, two closely related genes were identified by the Heisler lab to be regulated by the HD-ZIP III transcription factors and co-expressed adaxially with them in the Arabidopsis shoot and leaves. These genes encode transcription factors that share a similar MYB DNA binding domain to that of the KANADI transcription factors and were named KANLIKE1 (KANL1) and KANLIKE2 (KANL2). In this thesis, I investigate the role of KANL1 and KANL2 in the leaves of the Arabidopsis Ler ecotype in detail. I find that the lossof-function mutant kanl1 kanl2 exhibits a downward-curved leaf phenotype. Analyses of plants multiply mutant for members of the HD-ZIP III and KANL genes along with ChIP (Chromatin Extraction and Immunoprecipitation)-PCR results, further support the proposal that KANL1 and KANL2 are direct downstream targets of the HD-ZIP III transcription factors. Similar to findings previously reported for orthologs of the KANL genes in tomato and strawberry, I find that CUPSHAPED COTYLEDON2 (CUC2) and KNOTTED class 1 transcription factor KNAT1 are upregulated in Arabidopsis kanl1 kanl2 mutants. However, in kanl1 kanl2 leaves, I also find that the middle-domain-specific gene WUSCHEL-RELATED HOMEOBOX (WOX1) is expressed ectopically and that PRESSED FLOWER (PRS) is upregulated. By analysing the wox1 prs kanl1 kanl2 quadruple mutant, I find that the upwardly curving leaf phenotype of wox1 prs mutants is epistatic to the downward curving phenotype of kanl1 kanl2 mutants, indicating that KANL1 and KANL2 regulate leaf curvature in part by repressing both WOX1 and PRS expression. Lastly, by combining mutations in the KANL genes with mutations in ASYMMETRIC LEAVES 2 (AS2), another gene known to regulate leaf curvature and PRS/WOX expression, I infer that AS2 and the KANL genes act in parallel pathways.