Transcription factor that binds to DNA in promoters cis-regulatory element 5'-GGCGCGC-3' of cell cycle genes, including cyclins, cyclin-dependent kinases (CDKs), and components of the pre-replication complex (PubMed:20675570, PubMed:24687979). Binds to DNA in promoters cis-regulatory element 5'-AGCCG-3' of auxin regulated genes (e.g. PIN3 and PIN7) (PubMed:26578169). Together with FAMA and MYB88, ensures that stomata contain just two guard cells (GCs) by enforcing a single symmetric precursor cell division before stomatal maturity (PubMed:24571519). Represses the expression of the mitosis-inducing factors CDKB1-1 and CDKA-1, specifically required for the last guard mother cells (GMC) symmetric divisions in the stomatal pathway (PubMed:20675570, PubMed:24687979). Represses CYCA2-3 in newly formed guard cells (PubMed:21772250). Together with MYB88, regulates stomata spacing by restricting divisions late in the stomatal cell lineage thus limiting the number of GMC divisions (PubMed:11536724, PubMed:9684356, PubMed:16155180, PubMed:24123248). In collaboration with CDKB1-1 and CDKB1-2, restrict the G1/S transition and chloroplast and nuclear number during stomatal formation, and normally maintain fate and developmental progression throughout the stomatal cell lineage (PubMed:24123248). Also involved in the shape regulation of pavement cells (PubMed:9684356). Involved in sensing and/or transducing abiotic stress (e.g. drought and salt), probably via the positive regulation of NAC019 (PubMed:21105921). Regulates female reproduction being required for entry into megasporogenesis, probably via the regulation of cell cycle genes (PubMed:22915737). Promotes histone H3K27me3 marks and represses stem cell gene expression (PubMed:24654956). Required for lateral roots (LRs) initiation via the regulation of PIN3 expression in an auxin-dependent manner (PubMed:26578065). Involved in responses to gravity stimulation in primary roots by regulating the transcription of PIN3 and PIN7 in gravity-sensing cells, thus modulating auxin asymmetric redistribution (PubMed:26578169). Interacts with RBR1. Expressed in all shoot organs with higher levels in leaves, stems, flowers, siliques and floral buds. Also detected in roots tips. Expressed at the transition to terminal stomatal differentiation, just before and after the symmetric division of stomatal differentiation, being confined to late-stage guard mother cells (GMC) and to young, still differentiating guard cells (PubMed:16155180, PubMed:24571519). Detected in unopened flower buds, at the bases of sepals, petals, and stamens and in the receptacle of carpels, as well as both in style and stigma. Present at strong levels in the placenta within the ovary. Accumulates during ovule development in a dynamic pattern; first observed at high levels in the funiculus once integument outgrowth has begun and persists into later stages. Also expressed in the nucellus of younger ovules, especially in the megaspore mother cell (MMC) and in epidermal cells. Present in integuments, in the endothelial layer and the outer layer of the outer integument, which will form the mucilage-containing seed coat cells (PubMed:22915737). In developing embryos, first detected in cells in the ground tissue meristem at the early heart stage accumulates in the torpedo stage. In mature embryos, expressed in the embryonic hypocotyl and root tip. In seedlings, present first in the lower part of the hypocotyl and in the root tip, and later in petioles of cotyledons, young leaves, and lateral root primordia, near the pericycle. In young plants, strongly expressed in petioles of young leaves and cotyledons, especially in veins, in the basal part of young first leaves and cotyledons, and in root tips of lateral roots. Detected in the phloem, as well as in the cortex of inflorescence stems (PubMed:26391711). In roots, present in the root tip in columella cells, specifically in the lower tier of columella cells, as well as in developing metaxylem (PubMed:26391711, PubMed:26578169). Widely expressed in freshly emerged lateral roots. In elongating lateral roots, confined at high levels transiently in columella cells until differentiation (PubMed:26578169). Expressed at the base of developing flowers, including ovaries. In flowers, detected in ovaries, receptacles, and transiently, in anthers, and, later, in filaments. Also detected in the valve margins and receptacles of siliques and at the joint between the stigma and the style, as well as in the tapetum around pollen grains in maturing anthers (PubMed:26391711). Strongly induced by auxin in a IAA14/SLR1 and ARF7 dependent manner, especially in xylem pole pericycle cells, lateral roots initiating cells. Abnormal stomatal clusters formation composed by two to four adjacent stomata and some unpaired guard cells originating of extra symmetric divisions in cells with an abnormally persistent guard mother cell (GMC) identity (PubMed:11536724, PubMed:9684356, PubMed:16155180, PubMed:20675570). Abnormal stomatal cluster formation is complemented by FAMA (PubMed:24571519). Increased accumulation of CDKB1-1 in single flp-1 and double flp-1 myb88 mutants (PubMed:20675570). Induction of ectopic precursor cell division and delayed stomatal differentiation. End wall thickenings in all first generation GMCs (PubMed:16155180). Stronger accumulation of stomatal clusters separated by jigsaw-shaped pavement cells with wavy anticlinal walls in dorsiventral (e.g. cotyledons, sepals, and anthers) than in cylindrical organs (e.g. stems, flower stalks, and siliques), where pavement cells are rectangular (PubMed:9684356). Double mutants flp-7 myb88 and flp-1 myb88 have strong defects in stomata repartition with large stomatal clusters formation (PubMed:16155180). Double mutants flp-1 myb88 have increased susceptibility to drought and high salt (NaCl), as well as increased rates of water loss; these phenotypes are associated with reduced accumulation of many typical abiotic stress gene transcripts. Lower stomatal closure in response to abscisic acid (ABA) treatment (PubMed:21105921). Accumulation of CYCA2-3 in newly formed guard cells in flp-1 myb88 double mutant (PubMed:21772250). The double mutants flp-1 myb88 and flp-7 myb88 treated with oryzalin, a microtubule depolymerizing drug, exhibit round-to-oval-shaped single guard cells (sGCs) associated with increased DNA content due to endoreplication leading to 10C DNA levels. The quadruple mutant flp-1 myb88 cdkb1;1 cdkb1;2 has a reduced number of large single guard cells blocked at mitosis, with strongly altered shape and size and characterized by enlarged nucleus due to endomitosis and endocycling, as well as extensive chloroplast replication (PubMed:24123248). The double mutant flp-1 myb88 displays an enhanced stomatal phenotype with more and larger stomatal clusters. Triple mutants cdka;1 flp-1 myb88 don't have guard cells stacks but accumulates sGCs. Accumulation of CDKA-1 in the double mutant flp-1 myb88 (PubMed:24687979). Increased number of ovules produced by the placenta but reduced female fertility due to defective meiotic entry and progression, and subsequent altered embryo sac development, thus leading to reduced seed set (PubMed:22915737). Reduced numbers of lateral roots (LRs). The double mutants flp-1 myb88 and flp-7 myb88 lack lateral roots with reduced PIN3 levels (PubMed:26578065). Gravitropic defects in primary roots associated with a delayed auxin asymmetric redistribution due to reduced PIN3 and PIN7 levels (PubMed:26578169).