![]() In jaw-D, miR319a is overexpressed, which in turns down-regulates At TCP2, At TCP3, At TCP4, At TCP10, and At TCP24, resulting in plants which exhibit aberrant cell division, causing a serrated and crinkly leaf margin phenotype ( Palatnik et al., 2003). ![]() A subset of them, At TCP2, At TCP3, At TCP4, At TCP10, and At TCP24, are regulated by miR319a, produced by the JAW locus ( Palatnik et al., 2003). Functional analysis has been reported for most of the class II TCP genes. There are 24 predicted TCP proteins in the Arabidopsis genome, 13 class I and 11 class II proteins ( Cubas, 2002). Both class I and class II include members that can function as transcriptional activators and repressors ( Uberti Manassero et al., 2013). Mainly based on the TCP domain structure, class II TCP proteins can be subdivided into the CIN-like clade, with genes involved in lateral organ development such as CINCINNATA ( CIN) in Antirrhinum ( Nath et al., 2003), and the CYC/TB1 clade, with genes controlling axillary meristem development, such as TB1 in maize ( Doebley et al., 1997), and its orthologs in Arabidopsis ( Arabidopsis thaliana) BRANCHED1 ( BRC1/ TCP18) and BRANCHED2 ( BRC2/ TCP12) ( Aguilar-MartÃnez et al., 2007 Finlayson, 2007). TCP proteins can be classified into two groups based on differences in the structure of the TCP domain, known as class I (or PCF or TCP-P) and class II (or TCP-C). TCP genes code for proteins with a 59-amino acid non-canonical basic helix-loop-helix (bHLH), the TCP domain, involved in DNA binding and dimerization ( Cubas et al., 1999 Aggarwal et al., 2010). TCPs are a plant-specific family of transcription factors, named after the transcription factors TEOSINTE BRANCHED1 (TB1) in maize, CYCLOIDEA (CYC) in Antirrhinum majus, and PCF1 and PCF2 (for PROLIFERATING CELL NUCLEAR ANTIGEN FACTOR1 and 2) in rice ( Navaud et al., 2007 Busch and Zachgo, 2009). TCP factors are involved in the coordination of cell proliferation and cell differentiation, having roles in several aspects of plant development, such as regulation of the shoot apical meristem (SAM) ( Koyama et al., 2010 Li et al., 2012b), leaf development ( Palatnik et al., 2003 Ori et al., 2007), and lateral branching ( Doebley et al., 1997 Aguilar-MartÃnez et al., 2007). Plant architecture and organ form rely on developmental processes which involve the control of cell proliferation, cell growth and cell differentiation ( Ingram and Waites, 2006). Analysis of transgenic plants expressing AtTCP7-SRDX and AtTCP23-SRDX indicate a role of these factors in the control of cell proliferation. To circumvent the issue of genetic redundancy, dominant negative forms with SRDX repressor domain were used. We also determined that these factors are able to mutually interact in a yeast two-hybrid assay and regulate the expression of KNOX1 genes. We generated a pentuple mutant tcp8 tcp15 tcp21 tcp22 tcp23 and show that loss of function of these genes results in changes in leaf developmental traits. Gene redundancy is characteristic in this group, as also seen in the class II TCP genes. The similar expression pattern in young growing leaves found for this group suggests similarity in gene function. We studied a group of phylogenetically related class I TCP genes: At TCP7, At TCP8, At TCP22, and At TCP23. While the role of class II TCP genes in plant development is well known, data about the function of some class I TCP genes is lacking. ![]() This gene family is comprised of two groups, class I and class II. TCP family of plant-specific transcription factors regulates plant form through control of cell proliferation and differentiation.
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