Transcriptional repressor that regulates lateral organ polarity. Promotes lateral organ abaxial identity by repressing the adaxial regulator ASYMMETRIC LEAVES2 (AS2) in abaxial cells. Required for abaxial identity in both leaves and carpels. Functions with KAN2 in the specification of polarity of the ovule outer integument. Regulates cambium activity by repressing the auxin efflux carrier PIN1. Plays a role in lateral root formation and development. Expressed in developing phloem and lateral root. In globular embryos, expressed in the peripheral cells in a basal region above the hypophysis. In heart-stage embryos, expressed in the periphery of the presumptive hypocotyl and on the abaxial side of cotyledon primordia. During vegetative growth, expressed the abaxial side of very young leaf primordia. Expressed on the abaxial side of carpel primordia and then in a localized region on the abaxial margin that gives rise to the septum. Later, expressed in the tissue that gives rise to ovules. Repressed by AS2 in adaxial tissue. Flat leaves. Altered morphology of abaxial mesophyll cells. Decreased number of trichomes on the adaxial surface and increased number of abaxial trichomes. Plants overexpressing KAN1 develop elongated and pointed cotyledons and do not produced subsequent leaves, resulting in seedling lethality.