Required, together with OPS, for embryo provasculature development and cotyledon vascular complexity and connectivity (PubMed:25149602). Necessary, partially redundantly with DEAL2 and DEAL3, to ensure bilateral symmetry development and early leaf margin patterning, probably via the regulation of auxin and CUC2 distribution (PubMed:29139551). Regulates cell proliferation but not cell expansion (PubMed:29139551). Interacts with OPS. Expressed in vascular cells, mostly in hypocotyls, and, to a lower extent, in seedlings, roots, flowers, siliques, developing leaves and inflorescences, but barely in mature leaves and seeds (PubMed:25149602, PubMed:29139551). High levels in leaf primordia (PubMed:29139551). Mainly present in dividing tissues and fades out during cells differentiation, to reappear later in the vasculature (PubMed:29139551). Expressed in developing embryos and procambial, cambial, and vascular cells of cotyledons, leaves, roots, hypocotyls, and anthers (PubMed:25149602). During leaves development, first observed in leaf primordia, and becomes localized to the margins and the base of the lamina during the transition from cell proliferation to expansion and differentiation (PubMed:29139551). Later confined to petiole primordia (PubMed:29139551). Also detected in flower primordia (PubMed:29139551). Defects in vein connectivity early in mutant embryo development leading to reduced complexity of cotyledon vein networks and disconnected veins, including in embryos provasculatures (PubMed:25149602). The mutant deal1-1 exhibits a bilateral symmetry breaking but no obvious defects in dorsoventrality; early leaf primordia fail to acquire bilateral symmetry and instead form ectopic lobes and sinuses (PubMed:29139551). Developmental defects of pistils, some being bent or coiled or twisted, and some showing unfused carpels with exposed ovules (PubMed:29139551). In leaves, marginal cells expressing properly polarized PIN1 are badly recruited, thus leading to misplaced auxin maxima, as well as defects in cell proliferation but not in cell expansion (PubMed:29139551). Altered spatial pattern of CUC2 (PubMed:29139551). The double mutant vcc ops exhibits a complete loss of high-complexity vascular networks (PubMed:25149602). The vcc-3 deal2-1 and vcc-3 deal3-1 double mutants show leaf asymmetry (PubMed:29139551). The vcc-3 deal2-1 deal3-1 triple mutant shows a strong leaf asymmetry (PubMed:29139551). Belongs to the DESIGUAL family.