MADS-box transcription factors are key regulators of several plant development processes. Analysis of the complete Arabidopsis genome sequence revealed 107 genes encoding MADS-box proteins, of which 84% are of unknown function. Here, we provide a complete overview of this family, describing the gene structure, gene expression, genome localization, protein motif organization, and phylogenetic relationship of each member. We have divided this transcription factor family into five groups (named MIKC, M ␣ , M ␤ , M ␥ , and M ␦ ) based on the phylogenetic relationships of the conserved MADS-box domain. This study provides a solid base for functional genomics studies into this important family of plant regulatory genes, including the poorly characterized group of M-type MADS-box proteins. MADS-box genes also constitute an excellent system with which to study the evolution of complex gene families in higher plants.

Interactions between proteins are essential for their functioning and the biological processes they control. The elucidation of interaction maps based on yeast studies is a first step toward the understanding of molecular networks and provides a framework of proteins that possess the capacity and specificity to interact. Here, we present a comprehensive plant protein-protein interactome map of nearly all members of the Arabidopsis thaliana MADS box transcription factor family. A matrix-based yeast two-hybrid screen of >100 members of this family revealed a collection of specific heterodimers and a few homodimers. Clustering of proteins with similar interaction patterns pinpoints proteins involved in the same developmental program and provides valuable information about the participation of uncharacterized proteins in these programs. Furthermore, a model is proposed that integrates the floral induction and floral organ formation networks based on the interactions between the proteins involved. Heterodimers between flower induction and floral organ identity proteins were observed, which point to (auto)regulatory mechanisms that prevent the activity of flower induction proteins in the flower.

TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR1 (TCP) transcription factors control developmental processes in plants. The 24 TCP transcription factors encoded in the Arabidopsis (Arabidopsis thaliana) genome are divided into two classes, class I and class II TCPs, which are proposed to act antagonistically. We performed a detailed phenotypic analysis of the class I tcp20 mutant, showing an increase in leaf pavement cell sizes in 10-d-old seedlings. Subsequently, a glucocorticoid receptor induction assay was performed, aiming to identify potential target genes of the TCP20 protein during leaf development. The LIPOXYGENASE2 (LOX2) and class I TCP9 genes were identified as TCP20 targets, and binding of TCP20 to their regulatory sequences could be confirmed by chromatin immunoprecipitation analyses. LOX2 encodes for a jasmonate biosynthesis gene, which is also targeted by class II TCP proteins that are under the control of the microRNA JAGGED AND WAVY (JAW), although in an antagonistic manner. Mutation of TCP9, the second identified TCP20 target, resulted in increased pavement cell sizes during early leaf developmental stages. Analysis of senescence in the single tcp9 and tcp20 mutants and the tcp9tcp20 double mutants showed an earlier onset of this process in comparison with wild-type control plants in the double mutant only. Both the cell size and senescence phenotypes are opposite to the known class II TCP mutant phenotype in JAW plants. Altogether, these results point to an antagonistic function of class I and class II TCP proteins in the control of leaf development via the jasmonate signaling pathway. TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFER-ATING CELL FACTOR1 (TCP) proteins are plant-specific transcription factors that are involved in growth-related processes, such as branching, floral organ morphogenesis, and leaf growth (for review, see Martín-Trillo and Cubas, 2010). The Arabidopsis (Arabidopsis thaliana) genome encodes for 24 TCP transcription factor genes, which, based on sequence homology, are divided into two classes: class I and class II TCPs. Functional analysis of the Arabidopsis class II TCP genes BRANCHED1 (BRC1) and BRC2, both closely related to the TCP founder gene TEOSINTE BRANCHED1 from maize (Zea mays; Doebley et al., 1997), demonstrated that these genes are involved in suppressing axillary bud outgrowth (AguilarMartínez et al., 2007). Another subclass of the class II TCPs contains the genes TCP2, TCP3, TCP4, TCP10, and TCP24, which are all targets of the microRNA miR319a/ JAGGED AND WAVY (JAW; Palatnik et al., 2003). Simultaneous down-regulation of these five TCPs by ectopic expression of miR319a/JAW in jaw-D plants results in abnormal curvature and excessive growth of leaves. Conversely, expression of a hyperactivated form of TCP4 results in decreased cell proliferation and smaller

A yeast 3-hybrid screen in Arabidopsis reveals MADS box protein complexes: SEP3 is shown to mediate complex formation and floral timing.