Control of Pistil Development in Arabidopsis thaliana by a Novel Class of Regulatory Genes

Sammanfattning: The pistil, or the gynoecium, is the female reproductive organ of the angiosperm flower and its ontogeny has been studied in the model plant Arabidopsis thaliana. The mature Arabidopsis gynoecium consists of a basal ovary that contains the ovules, a short style and an apical stigma that serves as the site of pollen adherence and germination. This thesis describes the identification and functional characterisation of genes with roles in the regulation of Arabidopsis gynoecium development. Mutant analyses and sequence similarity database searches led to the identification of a small Arabidopsis gene family, denoted the SHI gene family, the ten members of which encode proteins with zinc finger-like motifs. This class of genes is novel and appears to be unique to plants.Double, triple and quadruple mutant analyses revealed that at least six of the SHI-related genes, STY1, STY2, SHI, SRS4, SRS5, and LRP1, redundantly contribute to the formation of stylar and stigmatic tissues in developing gynoecia. Several of the genes appear also to influence carpel fusion and vascular patterning in the gynoecium. Gynoecia of transgenic plants that express STY1 or STY2 constitutively develop ectopic style cells, confirming a role for the genes in the promotion of style formation. STY1, STY2, SHI and SRS5 are expressed in the apical parts of the developing gynoecium and, hence, likely act cell autonomously. As judged from mutant and overexpression analyses, the SHI-related genes appear also to regulate leaf development. Possibly, SHI family members act in concert with the plant growth hormones gibberellin and auxin.