ANGUSTIFOLIA (AN) controls leaf morphology in the plant Arabidopsis thaliana. Previous studies on sequence similarity demonstrated that the closest proteins to AN are members of animal C-terminal-binding proteins (CtBPs) found in nematodes, arthropods, and vertebrates. Drosophila CtBP (dCtBP) functions as a transcriptional corepressor for deoxyribonucleic acid (DNA)-binding repressors containing the short amino acid motif, PXDLS, to regulate tissue specification and segmentation during early embryogenesis. It has previously been shown that AN was thought to repress transcription similar to the function of CtBPs; however, AN lacks some of the structural features that are conserved in animal CtBPs. In this paper, we examined whether AN is functionally related to dCtBP. Firstly, we re-examined sequence similarity among AN and various CtBPs from several representative species in the plant and animal kingdoms. Secondly, yeast two-hybrid assays demonstrated that AN failed to interact with an authentic CtBP-interacting factor, adenovirus E1A oncoprotein bearing the PXDLS motif. Thirdly, AN tethered to DNA was unable to repress the expression of reporter genes in transgenic Drosophila embryos. Fourthly, overexpression assays suggested that dCtBP and AN function differently in Drosophila tissues. Finally, AN failed to rescue the zygotic lethality caused by dCtBP loss-of-function. These data, taken together, suggest that AN is functionally distinct from dCtBP. Likely, ancestral CtBPs acquired corepressor function (capability of both repression and binding to repressors containing the PXDLS motif) after the animal-plant divergence but before the protostome-deuterostome split. We therefore propose to categorize AN as a subfamily member within the CtBP/BARS/RIBEYE/AN superfamily.
Leaves are major photosynthetic organs, and their diverse shapes and sizes allow adaptation to the natural environment. The early control of leaf shape and size depends on the control of the rate and plane of cell division at the shoot apical meristem and the polarity‐dependent cell differentiation in the leaf primordium. In this review, we first summarize knowledge regarding several genes that control the initial stages of leaf formation and leaf polarity (e.g. adaxial–abaxial polarity, symmetry, and flat morphology). Formation of the lateral leaf morphology involves co‐ordination of the rates of division and enlargement of leaf cells. Thus, we also summarize information on a number of genes that control these stages of two‐dimensional lateral leaf growth (e.g. polarized cell expansion, specific control of cell proliferation, and integration of cell proliferation and expansion). In addition, we discuss several recently identified microRNAs, which are important factors affecting the development of leaf shape via control of spatial and temporal expression of target gene families. We focus on the genetic regulation of leaf shape in the model plant Arabidopsis thaliana from the perspective of spatial and temporal balance among cell proliferation, enlargement, and differentiation, with special emphasis on the results of our own studies.
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