Genetic Analysis of Leaf Margin Development Mediated by TALE Homeodomain Transcription Factors in Arabidopsis thaliana

Abstract

Plant leaves are one of the most prominent features of plants. After initiation from the shoot apical meristem, they form diverse leaf shapes in different species, determined by leaf morphogenesis. During this process, leaf margin development determines the outline of the leaf by producing interspaced leaf serrations, lobes, or leaflets, depending on the species and developmental stage of the plant. While several mechanisms explain how leaf serrations are formed, this process involves complex molecular pathways and combinations of three-dimensional leaf growth. In Arabidopsis, the TALE transcription factor superfamily, which consists of the BLH and KNOX subfamilies, regulates a wide range of developmental processes. Among a total of thirteen BLH proteins, SAW1 and SAW2 act redundantly in leaf margin development. This study focused on the genetic characterisation of SAWs as well as the investigation of their relationships with other TALE members. Detailed analyses suggested interesting genetic properties of SAW1 based on extensive phenotypic observations and expression analyses using different tissue-specific promoters. These studies proposed a novel perspective for the role of SAW1 in leaf development, suggesting that SAW1 is involved in the timing of initiation of leaf serrations. Furthermore, the generation of complete loss-of-function mutant of SAW showed a more extensive leaf margin defect, indicating a role of the SAW genes in regulation of the even distribution of marginal serrations. Moreover, combinations of TALE mutant alleles identified specific TALE proteins which might be involved in repressing and promoting leaf serrations in the absence of SAW. Consequently, this study sheds light on the role of TALE transcription factors in leaf margin development.