The MADS-box family of transcription factors

Functional conservation of MIKC*-Type MADS box genes in Arabidopsis and rice pollen maturation

There are two groups of MADS intervening keratin-like and C-terminal (MIKC)-type MADS box genes, MIKC(C) type and MIKC* type. In seed plants, the MIKC(C) type shows considerable diversity, but the MIKC* type has only two subgroups, P- and S-clade, which show conserved expression in the gametophyte. To examine the functional conservation of MIKC*-type genes, we characterized all three rice (Oryza sativa) MIKC*-type genes. All three genes are specifically expressed late in pollen development. The single knockdown or knockout lines, respectively, of the S-clade MADS62 and MADS63 did not show a mutant phenotype, but lines in which both S-clade genes were affected showed severe defects in pollen maturation and germination, as did knockdown lines of MADS68, the only P-clade gene in rice. The rice MIKC*-type proteins form strong heterodimeric complexes solely with partners from the other subclade; these complexes specifically bind to N10-type C-A-rich-G-boxes in vitro and regulate downstream gene expression by binding to N10-type promoter motifs. The rice MIKC* genes have a much lower degree of functional redundancy than the Arabidopsis thaliana MIKC* genes. Nevertheless, our data indicate that the function of heterodimeric MIKC*-type protein complexes in pollen development has been conserved since the divergence of monocots and eudicots, roughly 150 million years ago.

Analysis of the expression of the AGL17-like clade of MADS-box transcription factors in rice

In plants, MADS-box transcription factors are key regulators of floral and fruit development, organ dehiscence and stress responses. Nevertheless, the functions of most of them are still unknown. In Arabidopsis thaliana, the AGL17-like clade of MADS-box transcription factors comprises four members. AGL17 is involved in floral induction, whereas AGL44/ANR1 is involved in the adaptive development of roots in response to nitrate. AGL21 is primarily expressed in the roots and AGL16 in the leaves, suggesting that these transcription factors may be involved in the control of vegetative development. In Oryza sativa, the AGL17-like clade comprises five members, OsMADS23, OsMADS25, OsMADS27, OsMADS57 and OsMADS61. In a first attempt to characterize their functions, we used promoter::Gus reporter gene fusions and RT-qPCR to study the expression patterns of these genes and their regulation by different external stimuli. The OsMADS23, OsMADS25, OsMADS27 and OsMADS57 promoters were active in the root's central cylinder. In addition, the OsMADS57 promoter was active in leaves, whereas the OsMADS61 promoter was only active in the leaf tips and the stem base. OsMADS25 and OsMADS27 transcripts accumulated in response to osmotic stress, whereas the expression levels of OsMADS25, OsMADS27 and OsMADS57 were slightly induced by nitrate. Each of these five genes was responsive to various hormonal treatments. These distinct expression patterns indicate that these five genes have specific and non-redundant functions that likely differs from those of their A. thaliana homologs.

Over-expression of the PaAP1 gene from sweet cherry (Prunus avium L.) causes early flowering in Arabidopsis thaliana

A homologue of SQUAMOSA/APETALA1, designated PaAP1, was isolated from Prunus avium by reverse transcription-PCR (RT-PCR). The full length of PaAP1 cDNA is 753 bp, and it codes for a polypeptide of 250 amino acid residues. Sequence comparison revealed that PaAP1 belongs to the MADS-box gene family. Phylogenetic analysis indicated that PaAP1 shared the highest identity with SQUA/AP1 homologues from Prunus serrulata. Real-time fluorescence quantitative PCR analysis showed that PaAP1 was expressed at high levels in petal, sepal, style, and flower buds, which was slightly different from the expression pattern of AP1 of Arabidopsis thaliana. To characterize the functions of PaAP1, we assessed Arabidopsis transformed with 35S::PaAP1. A total of 8 transgenic T(1) lines with an early flowering phenotype were obtained, and a 3:1 segregation ratio of flowering time was observed in the T(2) generation of 4 lines. This study provides the first functional analysis of an SQUA/AP1 homolog from P. avium and suggests that PaAP1 is potentially useful for shortening the juvenile period in sweet cherry.

Exon skipping of AGAMOUS homolog PrseAG in developing double flowers of Prunus lannesiana (Rosaceae)

KEY MESSAGE : Two transcript isoforms of AGAMOUS homologs, from single and double flower Prunus lannesiana, respectively, showed different functions. The Arabidopsis floral homeotic C function gene AGAMOUS (AG) confers stamen and carpel identity. Loss of AG function results in homeotic conversions of stamens into petals and formation of double flowers. In order to present a molecular dissection of a double-flower cultivar in Prunus lannesiana (Rosaceae), we isolated and identified a single-copy gene, AG homolog from two genetically cognate P. lannesiana bearing single and double flowers, respectively. Sequence analysis revealed that the AG homolog, prseag-1, from double flowers showed a 170-bp exon skipping as compared to PrseAG (Prunus serrulata AGAMOUS) from the single flowers. Genomic DNA sequence revealed that abnormal splicing resulted in mutant prseag-1 protein with the C-terminal AG motifs I and II deletions. In addition, protein sequence alignment and phylogenetic analyses revealed that the PrseAG was grouped into the euAG lineage. A semi-quantitative PCR analysis showed that the expression of PrseAG was restricted to reproductive organs of stamens and carpels in single flowers of P. lannesiana 'speciosa', while the prseag-1 mRNA was highly transcribed throughout the petals, stamens, and carpels in double flowers from 'Albo-rosea'. The transgenic Arabidopsis containing 35S::PrseAG displayed extremely early flowering, bigger stamens and carpels and homeotic conversion of petals into staminoid organs, but ectopic expression of prseag-1 could not mimic the phenotypic ectopic expression of PrseAG in Arabidopsis. In general, this study provides evidences to show that double flower 'Albo-rosea' is a putative C functional ag mutant in P. lannesiana.

Complex modulation of the Aedes aegypti transcriptome in response to dengue virus infection

Dengue fever is the most important arboviral disease world-wide, with Aedes aegypti being the major vector. Interactions between the mosquito host and dengue viruses (DENV) are complex and vector competence varies among geographically-distinct Ae. aegypti populations. Additionally, dengue is caused by four antigenically-distinct viral serotypes (DENV1–4), each with multiple genotypes. Each virus genotype interacts differently with vertebrate and invertebrate hosts. Analyses of alterations in mosquito transcriptional profiles during DENV infection are expected to provide the basis for identifying networks of genes involved in responses to viruses and contribute to the molecular-genetic understanding of vector competence. In addition, this knowledge is anticipated to support the development of novel disease-control strategies. RNA-seq technology was used to assess genome-wide changes in transcript abundance at 1, 4 and 14 days following DENV2 infection in carcasses, midguts and salivary glands of the Ae. aegypti Chetumal strain. DENV2 affected the expression of 397 Ae. aegypti genes, most of which were down-regulated by viral infection. Differential accumulation of transcripts was mainly tissue- and time-specific. Comparisons of our data with other published reports reveal conservation of functional classes, but limited concordance of specific mosquito genes responsive to DENV2 infection. These results indicate the necessity of additional studies of mosquito-DENV interactions, specifically those focused on recently-derived mosquito strains with multiple dengue virus serotypes and genotypes.

Transcriptional responses in Enchytraeus albidus (Oligochaeta): comparison between cadmium and zinc exposure and linkage to reproduction effects

Metal ecotoxicity to soil organisms (for example, in enchytraeids) has been addressed mainly by assessing effects on survival and reproduction, but very little is known about the underlying molecular mechanisms of responses. The main purpose of the present study was to assess and compare the transcriptional responses of Enchytraeus albidus to an essential (Zn) and a nonessential (Cd) metal. Exposure was performed with two concentrations with a known effect on reproduction (effective concentration for 50% [EC50] and 90% [EC90]) at three time points (2, 4, and 8 d). Results showed that transcriptional responses were influenced by exposure duration but, independently of that, the mechanisms of response to Cd and Zn were consistently different. Both metals affected pathways related to the regulation of gene expression, calcium homeostasis, and cellular respiration. Mechanisms of toxicity that were exclusively associated with Cd exposures were the inhibition of DNA repair and the impairment of ubiquitin-mediated proteolysis. The microarray for E. albidus was a useful tool for detecting molecular pathways affected by metal exposures. Transcriptional responses strongly correlated with known mechanisms of Cd and Zn responses in other organisms, suggesting cross-species conserved mechanisms of action. It should be highlighted not only that the authors could retrieve mechanistic information but also that genes responded within 2 to 8 d of exposure. This represents an additional advantage of using such molecular endpoints as a complement to the traditional, more time-consuming endpoints.

Characterization of SOC1's central role in flowering by the identification of its upstream and downstream regulators

The transition from vegetative to reproductive development is one of the most important phase changes in the plant life cycle. This step is controlled by various environmental signals that are integrated at the molecular level by so-called floral integrators. One such floral integrator in Arabidopsis (Arabidopsis thaliana) is the MADS domain transcription factor SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1). Despite extensive genetic studies, little is known about the transcriptional control of SOC1, and we are just starting to explore the network of genes under the direct control of SOC1 transcription factor complexes. Here, we show that several MADS domain proteins, including SOC1 heterodimers, are able to bind SOC1 regulatory sequences. Genome-wide target gene analysis by ChIP-seq confirmed the binding of SOC1 to its own locus and shows that it also binds to a plethora of flowering-time regulatory and floral homeotic genes. In turn, the encoded floral homeotic MADS domain proteins appear to bind SOC1 regulatory sequences. Subsequent in planta analyses revealed SOC1 repression by several floral homeotic MADS domain proteins, and we show that, mechanistically, this depends on the presence of the SOC1 protein. Together, our data show that SOC1 constitutes a major hub in the regulatory networks underlying floral timing and flower development and that these networks are composed of many positive and negative autoregulatory and feedback loops. The latter seems to be crucial for the generation of a robust flower-inducing signal, followed shortly after by repression of the SOC1 floral integrator.

Regulation of serum response factor by miRNA-200 and miRNA-9 modulates oligodendrocyte progenitor cell differentiation

Serum response factor (SRF) is a transcription factor that transactivates actin-associated genes and has been implicated in oligodendrocyte (OL) differentiation. To date, it has not been investigated in cerebral ischemia. We investigated the dynamics of SRF expression after stroke in vivo and the role of SRF in OL differentiation in vitro. Using immunohistochemistry, we found that SRF was upregulated in OLs and OL precursor cells (OPCs) after stroke. Moreover, upregulation of SRF was concurrent with downregulation of the micro-RNAs (miRNAs) miR-9 and the miR-200 family in the ischemic white matter region, the corpus callosum. Inhibition of SRF activation by CCG-1423, a specific inhibitor of SRF function, blocked OPCs from differentiating into OLs. Overexpression of miR-9 and miR-200 in cultured OPCs suppressed SRF expression and inhibited OPC differentiation. Moreover, co-expression of miR-9 and miR-200 attenuated activity of a luciferase reporter assay containing the Srf 3' untranslated region. Collectively, this study is the first to show that stroke upregulates SRF expression in OPCs and OLs, and that SRF levels are mediated by miRNAs and regulate OPC differentiation.

Serum response factor regulates bone formation via IGF-1 and Runx2 signals

Serum response factor (SRF) plays vital roles in numerous cellular processes; however, the physiological function of SRF in skeletal tissue remains unknown. In several organ systems, SRF regulates the expression of insulin-like growth factor-1 (IGF-1), which is crucial for normal development of mineralized skeleton and bone remodeling throughout life. Here, we show that conditional deletion of SRF in osteoblasts by osteocalcin-Cre generated viable mice with normal body size and body weight. Compared with normal siblings, osteoblast-specific SRF-deficient adult mice exhibited a marked decrease in bone mineral density and bone formation rate. Deletion of SRF in primary mouse calvarial osteoblasts reduced cell differentiation and mineralization in vitro. This was accompanied by a decrease in IGF-1 expression and secretion. Addition of IGF-1 in the culture media enhanced osteoblast differentiation in control cells and partially restored the mineralization defect of SRF-deficient cells, supporting an important role of SRF in regulating IGF-1 and IGF-1-mediated osteoblast differentiation. IGF-1-induced Akt activation was inhibited in SRF-deficient calvarial cells and enhanced in the SRF overexpressed cells. In addition, SRF deficiency decreased the transcriptional activity of Runx2, the key transcription factor for osteogenesis. Overexpression of SRF induced Runx2 transactivity in control cells and restored Runx2 transactivity in the SRF-deficient cells. Taken together, we conclude that SRF is important for IGF-1-induced osteoblast differentiation and mineralization via regulating IGF-1 expression and Runx2 transactivity.

Genome-wide identification of SOC1 and SVP targets during the floral transition in Arabidopsis

Floral transition in Arabidopsis is tightly controlled by complex genetic regulatory networks in response to endogenous and environmental flowering signals. SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and SHORT VEGETATIVE PHASE (SVP), two key MADS-domain transcription factors, perceive these signals and function as antagonistic flowering regulators. To understand how these factors mediate floral transition, we mapped in vivo binding sites of SOC1 and SVP using chromatin immunoprecipitation followed by hybridization to whole-genome tiling arrays (ChIP-chip). Genes that encoded proteins with transcription regulator activity and transcription factor activity were the most enriched groups of genes of those bound by SOC1 and SVP, which indicates their central roles in flowering regulatory networks. In combination with gene expression microarray studies, we further identified the genes whose expression was controlled directly by SOC1 or SVP. Among the common direct targets identified, APETALA2 (AP2)-like genes that repress FT and SOC1 expression were down-regulated by SOC1, but up-regulated by SVP, revealing a complex feedback regulation among the key genes that determine the integration of flowering signals. SOC1 regulatory regions were also accessed by SOC1 itself and SVP, suggesting that self-activation and repression by SVP contribute to the control of SOC1 expression. In addition, ChIP-chip analysis demonstrated that miR156e and miR172a, which are involved in the regulation of AP2-like genes, were direct targets of SOC1 and SVP, respectively. Taken together, these findings revealed that feedback regulatory loops mediated by SOC1 and SVP are essential components of the gene regulatory networks that underpin the integration of flowering signals during floral transition.

A split luciferase complementation assay for studying in vivo protein-protein interactions in filamentous ascomycetes

Protein-protein interactions play important roles in controlling many cellular events. To date, several techniques have been developed for detection of protein-protein interactions in living cells, among which split luciferase complementation has been applied in animal and plant cells. Here, we examined whether the split luciferase assay could be used in filamentous ascomycetes, such as Gibberella zeae and Cochliobolus heterostrophus. The coding sequences of two strongly interacting proteins (the F-box protein, FBP1, and its partner SKP1) in G. zeae, under the control of the cryparin promoter from Cryphonectria parasitica, were translationally fused to the C- and N-terminal fragments of firefly luciferase (luc), respectively. Each fusion product inserted into a fungal transforming vector carrying the gene for resistance to either geneticin or hygromycin B, was transformed into both fungi. We detected complementation of split luciferase proteins driven by interaction of the two fungal proteins with a high luminescence intensity-to-background ratio only in the fungal transformants expressing both N-luc and C-luc fusion constructs. Using this system, we also confirmed a novel protein interaction between transcription factors, GzMCM1 and FST12 in G. zeae, which could hardly be proven by the yeast two-hybrid method. This is the first study demonstrating that monitoring of split luciferase complementation is a sensitive and efficient method of studying in vivo protein-protein interactions in filamentous ascomycetes.

MEF2C ablation in endothelial cells reduces retinal vessel loss and suppresses pathologic retinal neovascularization in oxygen-induced retinopathy

Ischemic retinopathies, including retinopathy of prematurity and diabetic retinopathy, are major causes of blindness. Both have two phases, vessel loss and consequent hypoxia-driven pathologic retinal neovascularization, yet relatively little is known about the transcription factors regulating these processes. Myocyte enhancer factor 2 (MEF2) C, a member of the MEF2 family of transcription factors that plays an important role in multiple developmental programs, including the cardiovascular system, seems to have a significant functional role in the vasculature. We, therefore, generated endothelial cell (EC)-specific MEF2C-deficient mice and explored the role of MEF2C in retinal vascularization during normal development and in a mouse model of oxygen-induced retinopathy. Ablation of MEF2C did not cause appreciable defects in normal retinal vascular development. However, MEF2C ablation in ECs suppressed vessel loss in oxygen-induced retinopathy and strongly promoted vascular regrowth, consequently reducing retinal avascularity. This finding was associated with suppression of pathologic retinal angiogenesis and blood-retinal barrier dysfunction. MEF2C knockdown in cultured retinal ECs using small-interfering RNAs rescued ECs from death and stimulated tube formation under stress conditions, confirming the endothelial-autonomous and antiangiogenic roles of MEF2C. HO-1 was induced by MEF2C knockdown in vitro and may play a role in the proangiogenic effect of MEF2C knockdown on retinal EC tube formation. Thus, MEF2C may play an antiangiogenic role in retinal ECs under stress conditions, and modulation of MEF2C may prevent pathologic retinal neovascularization.

Identification and characterization of lineage-specific highly conserved noncoding sequences in Mammalian genomes

Vertebrate genome comparisons revealed that there are highly conserved noncoding sequences (HCNSs) among a wide range of species and many of which contain regulatory elements. However, recently emerged sequences conserved in specific lineages have not been well studied. Toward this end, we identified 8,198 primate and 21,128 specific HCNSs as representative ones among mammals from human-marmoset and mouse-rat comparisons, respectively. Derived allele frequency analysis of primate-specific HCNSs showed that these HCNSs were under purifying selection, indicating that they may harbor important functions. We selected the top 1,000 largest HCNSs and compared the lineage-specific HCNS-flanking genes (LHF genes) with ultraconserved element (UCE)-flanking genes. Interestingly, the majority of LHF genes were different from UCE-flanking genes. This lineage-specific set of LHF genes was more enriched in protein-binding function. Conversely, the number of LHF genes that were also shared by UCEs was small but significantly larger than random expectation, and many of these genes were involved in anatomical development as transcriptional regulators, suggesting that certain groups of genes preferentially recruit new HCNSs in addition to old HCNSs that are conserved among vertebrates. This group of LHF genes might be involved in the various levels of lineage-specific evolution among vertebrates, mammals, primates, and rodents. If so, the emergence of HCNSs in and around these two groups of LHF genes developed lineage-specific characteristics. Our results provide new insight into lineage-specific evolution through interactions between HCNSs and their LHF genes.

Functional conservation and diversification between rice OsMADS22/OsMADS55 and Arabidopsis SVP proteins

MADS-box transcription factors play pivotal roles in several aspects of plant growth and development. The Arabidopsis SHORT VEGETATIVE PHASE (SVP) protein mediates the integration of signals involved in the control of flowering time and flower development by interacting with MADS-box proteins. In the rice genome, three SVP-like genes (OsMADS22, OsMADS47, and OsMADS55) are present. To investigate the functional conservation of these SVP-like genes in rice and Arabidopsis, the phenotypes of transgenic Arabidopsis plants overexpressing OsMADS22 and OsMADS55 were analyzed. Overexpression of OsMADS22 and OsMADS55 led to abnormal floral morphologies including leaf-like sepals, whereas only OsMADS55 expression caused delayed flowering via downregulation of FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1). Yeast two-hybrid assays revealed that OsMADS22 and OsMADS55 interacted with Arabidopsis AGL24 and AP1, but only OsMADS55 interacted with FLC. Overexpression of OsMADS55, but not OsMADS22, complemented the early flowering phenotype and ambient temperature-insensitive flowering phenotype seen in svp mutants, suggesting that OsMADS55 regulates flowering time associated with ambient temperature responses in Arabidopsis. Taken together, our data are consistent with functional conservation and diversification between Arabidopsis and rice SVP-like genes involved in controlling flowering time and flower development.

Cardiac expression of ms1/STARS, a novel gene involved in cardiac development and disease, is regulated by GATA4

Ms1/STARS is a novel muscle-specific actin-binding protein that specifically modulates the myocardin-related transcription factor (MRTF)-serum response factor (SRF) regulatory axis within striated muscle. This ms1/STARS-dependent regulatory axis is of central importance within the cardiac gene regulatory network and has been implicated in cardiac development and postnatal cardiac function/homeostasis. The dysregulation of ms1/STARS is associated with and causative of pathological cardiac phenotypes, including cardiac hypertrophy and cardiomyopathy. In order to gain an understanding of the mechanisms governing ms1/STARS expression in the heart, we have coupled a comparative genomic in silico analysis with reporter, gain-of-function, and loss-of-function approaches. Through this integrated analysis, we have identified three evolutionarily conserved regions (ECRs), α, SINA, and DINA, that act as cis-regulatory modules and confer differential cardiac cell-specific activity. Two of these ECRs, α and DINA, displayed distinct regulatory sensitivity to the core cardiac transcription factor GATA4. Overall, our results demonstrate that within embryonic, neonatal, and adult hearts, GATA4 represses ms1/STARS expression with the pathologically associated depletion of GATA4 (type 1/type 2 diabetic models), resulting in ms1/STARS upregulation. This GATA4-dependent repression of ms1/STARS expression has major implications for MRTF-SRF signaling in the context of cardiac development and disease.

Cloning and expression analysis of a PISTILLATA homologous gene from pineapple (Ananas comosus L. Merr)

PISTILLATA (PI)-like genes are crucial regulators of flowering in angiosperms. A homologue of PI, designated as AcPI (Genbank accession number HQ717796), was isolated from pineapple cultivar Comte de Paris by reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The cDNA sequence of AcPI is 907 bp in length and contains an open reading frame of 594 bp, which encodes a protein of 197 amino acids. The molecular weight was 2.29 kDa and the isoelectric point was 9.28. The alignment showed that AcPI had a high identity with CsPIC2 (78.6%), AoPI (77.4%), OrcPI (75.7%) and HPI2 (72.4%). Quantitative real-time polymerase chain reaction (qRT-PCR) analyses in different tissues showed that the expression pattern of AcPI was different from the B-class genes in eudicots. AcPI was expressed in all the tissues investigated. The expression level was very low in fruit stems, bracts, leaves and sepals, high in petals and carpels, and moderate in apical meristems, flesh and stamens. The qRT-PCR analyses in different stages indicated that the expression of AcPI reached the highest level at 40 days after flower inducement, when the multiple fruit and floral organs were forming. It proved the important role of AcPI in floral organs and fruit development. The 35S::AcPI transgenic Arabidopsis plants flowered earlier and had more inflorescences or branches than wild type plants.

UTX, a histone H3-lysine 27 demethylase, acts as a critical switch to activate the cardiac developmental program

The removal of histone H3 lysine27 (H3K27) trimethylation mark is important for the robust induction of many cell type-specific genes during differentiation. Here we show that UTX, a H3K27 demethylase, acts as a critical switch to promote a cardiac-specific gene program. UTX-deficient ESCs failed to develop heart-like rhythmic contractions under a cardiac differentiation condition. UTX-deficient mice show severe defects in heart development and embryonic lethality. We found that UTX is recruited to cardiac-specific enhancers by associating with core cardiac transcription factors and demethylates H3K27 residues in cardiac genes. In addition, UTX facilitates the recruitment of Brg1 to the cardiac-specific enhancers. Together, our data reveal key roles for UTX in a timely transition from poised to active chromatin in cardiac genes during heart development and a fundamental mechanism by which a H3K27 demethylase triggers tissue-specific chromatin changes.

Myocardin-related transcription factor-A complexes activate type I collagen expression in lung fibroblasts

Pulmonary fibrosis is characterized by the excessive deposition of a collagen-rich extracellular matrix. The accumulation of collagen within the lung interstitium leads to impaired respiratory function. Furthermore, smooth muscle actin-positive myofibroblasts within the fibrotic lung contribute to disease progression. Because collagen and smooth muscle cell α-actin are coordinately expressed in the setting of fibrosis, the hypothesis was tested that specific transcriptional regulators of the myocardin family might also regulate collagen gene expression in myofibroblasts. Myocardin-related transcription factors (MRTFs), through their interaction with the serum-response factor (SRF) on CArG box regulatory elements (CC(A/T)6GG), are important regulators of myofibroblast differentiation. MRTF-A transactivated type I collagen gene reporters as much as 100-fold in lung myofibroblasts. Loss of functional MRTF-A using either a dominant negative MRTF-A isoform, shRNA targeting MRTF-A, or genetic deletion of MRTF-A in lung fibroblasts significantly disrupted type I collagen synthesis relative to controls. Analysis of the COL1A2 proximal promoter revealed a noncanonical CArG box (CCAAACTTGG), flanked by several Sp1 sites important for MRTF-A activation. Chromatin immunoprecipitation experiments confirmed the co-localization of MRTF-A, SRF, and Sp1 bound to the same region of the COL1A2 promoter. Mutagenesis of either the noncanonical CArG box or the Sp1 sites significantly disrupted MRTF-A activation of COL1A2. Together, our findings show that MRTF-A is an important regulator of collagen synthesis in lung fibroblasts and exhibits a dependence on both SRF and Sp1 function to enhance collagen expression.

Functional genomics of a living fossil tree, Ginkgo, based on next-generation sequencing technology

Ginkgo biloba is monotypic species native to China and has old, dioecious, medicinally important characteristics. The functional genes related to these characteristics have not been effectively explored due to a limited number of expressed sequence tags (ESTs) from Ginkgo. To discover novel functional genes efficiently and to understand the development of a living fossil tree, Ginkgo, we used massive parallel pyrosequencing on the Roche 454 GS FLX Titanium platform to generate 64 057 ESTs. The ESTs combined with the 21 590 Ginkgo ESTs in genbank were assembled into 22 304 unique putative transcripts, in which 13 922 novel unique putative transcripts were identified by 454 sequencing. After being assigned to putative functions with Gene Ontology terms, a detailed view of the Ginkgo biological systems was displayed, including characterization of unique putative transcripts with homology to known key enzymes and transcription factors involved in ginkgolide/bilobalide and flavonoid biosynthetic pathways, as well as unique putative transcripts related to development, response to disease and defence. The fact that three full-length Ginkgo genes encoding key enzymes were found and cloned, suggests that high-throughput sequencing technology is superior to traditional gene-by-gene approach in discovery of genes. Additionally, a total of 204 simple sequence repeat motifs were detected. Our study not only lays the foundations for transcriptome-led studies in biosynthetic mechanisms, but also contributes significantly to the understanding of functional genomics and development in non-model plants.

Multiple cis-elements in the 5'-flanking region of embryonic/larval fast-type of the myosin heavy chain gene of torafugu, MYH(M743-2), function in the transcriptional regulation of its expression

The myosin heavy chain gene, MYH(M743-2), is highly expressed in fast muscle fibers of torafugu embryos and larvae, suggesting its functional roles for embryonic and larval muscle development. However, the transcriptional regulatory mechanism involved in its expression remained unknown. Here, we analyzed the 2075bp 5'-flanking region of torafugu MYH(M743-2) to examine the spatial and temporal regulation by using transgenic and transient expression techniques in zebrafish embryos. Combining both transient and transgenic analyses, we demonstrated that the 2075bp 5'-flanking sequences was sufficient for its expression in skeletal, craniofacial and pectoral fin muscles. The immunohistochemical observation revealed that the zebrafish larvae from the stable transgenic line consistently expressed enhanced green fluorescent protein (EGFP) in fast muscle fibers. Promoter deletion analyses demonstrated that the minimum 468bp promoter region could direct MYH(M743-2) expression in zebrafish larvae. We discovered that the serum response factor (SRF)-like binding sites are required for promoting MYH(M743-2) expression and myoblast determining factor (MyoD) and myocyte enhancer factor-2 (MEF2) binding sites participate in the transcriptional control of MYH(M743-2) expression in fast skeletal muscles. We further discovered that MyoD binding sites, but not MEF2, participate in the transcriptional regulation of MYH(M743-2) expression in pectoral fin and craniofacial muscles. These results clearly demonstrated that multiple cis-elements in the 5'-flanking region of MYH(M743-2) function in the transcriptional control of its expression.

RTVP-1 expression is regulated by SRF downstream of protein kinase C and contributes to the effect of SRF on glioma cell migration

Gliomas are characterized by increased infiltration into the surrounding normal brain tissue. We recently reported that RTVP-1 is highly expressed in gliomas and plays a role in the migration of these cells, however the regulation of RTVP-1 expression in these cells is not yet described. In this study we examined the role of PKC in the regulation of RTVP-1 expression and found that PMA and overexpression of PKCα and PKCε increased the expression of RTVP-1, whereas PKCδ exerted an opposite effect. Using the MatInspector software, we identified a SRF binding site on the RTVP-1 promoter. Chromatin immunoprecipitation (ChIP) assay revealed that SRF binds to the RTVP-1 promoter in U87 cells, and that this binding was significantly increased in response to serum addition. Moreover, silencing of SRF blocked the induction of RTVP-1 expression in response to serum. We found that overexpression of PKCα and PKCε increased the activity of the RTVP-1 promoter and the binding of SRF to the promoter. In contrast, overexpression of PKCδ blocked the increase in RTVP-1 expression in response to serum and the inhibitory effect of PKCδ was abrogated in cells expressing a SRFT160A mutant. SRF regulated the migration of glioma cells and its effect was partially mediated by RTVP-1. We conclude that RTVP-1 is a PKC-regulated gene and that this regulation is at least partly mediated by SRF. Moreover, RTVP-1 plays a role in the effect of SRF on glioma cell migration.

Regulation of myocyte enhancer factor-2 transcription factors by neurotoxins

Various isoforms of myocyte enhancer factor-2 (MEF2) constitute a group of nuclear proteins found to play important roles in increasing types of cells. In neurons, MEF2s are required to regulate neuronal development, synaptic plasticity, as well as survival. MEF2s promote the survival of several types of neurons under different conditions. In cellular models, negative regulation of MEF2s by stress and toxic signals contributes to neuronal death. In contrast, enhancing MEF2 activity not only protects cultured primary neurons from death in vitro but also attenuates the loss of dopaminergic neurons in substantia nigra pars compacta in a 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine mouse model of Parkinson's disease. In this work, the mechanisms of regulation of MEF2 function by several well-known neurotoxins and their implications in various neurodegenerative diseases are reviewed.

Isolation and characterization of an AGAMOUS-like gene from Hosta plantaginea

Based on genetic and molecular analyses, the ABC model was proposed to explain the genetic control of floral development. The C-class MADS box gene AGAMOUS (AG) plays crucial roles in Arabidopsis thaliana development through regulation of the organ identity of stamens and gynoecium. The present research reports for the first time the cloning of an AG homologue (HpAG) from Hosta plantaginea Aschers. Phylogenetic analysis shows HpAG is a homologue of AG that is closely related to C-lineage AG homologues from monocot species. Semi-quantitative PCR and real-time PCR analyses show that HpAG is stamen- and gynoecium-specific in expression and has spatial and temporal expression patterns in the reproductive organs of H. plantaginea. The transcriptional activation property of HpAG is also verified by a yeast one-hybrid. Functional analysis is carried out in Arabidopsis by overexpression of HpAG. The homeotic transformations of petals into staminoid organs are observed in 35S::HpAG transgenic plants. All these results show that HpAG1 plays a crucial role in stamen specification and gynoecium development.

Coping with stresses: roles of calcium- and calcium/calmodulin-regulated gene expression

Abiotic and biotic stresses are major limiting factors of crop yields and cause billions of dollars of losses annually around the world. It is hoped that understanding at the molecular level how plants respond to adverse conditions and adapt to a changing environment will help in developing plants that can better cope with stresses. Acquisition of stress tolerance requires orchestration of a multitude of biochemical and physiological changes, and most of these depend on changes in gene expression. Research during the last two decades has established that different stresses cause signal-specific changes in cellular Ca(2+) level, which functions as a messenger in modulating diverse physiological processes that are important for stress adaptation. In recent years, many Ca(2+) and Ca(2+)/calmodulin (CaM) binding transcription factors (TFs) have been identified in plants. Functional analyses of some of these TFs indicate that they play key roles in stress signaling pathways. Here, we review recent progress in this area with emphasis on the roles of Ca(2+)- and Ca(2+)/CaM-regulated transcription in stress responses. We will discuss emerging paradigms in the field, highlight the areas that need further investigation, and present some promising novel high-throughput tools to address Ca(2+)-regulated transcriptional networks.

Substitution pattern of the CArG element in human and mouse genomes

cis-Elements CArG bound by serum response factor (SRF) are presently being intensively studied, but little is known about the substitution pattern of functional CArG elements. Here, we have performed the first evolutionary analysis of CArGome in the human and mouse genome through bioinformatic methods and statistical tests. We calculated the substitution rate at each site of the functional CArG elements. The results showed that the core sites of the functional CArG elements evolved faster than did the background DNA, indicating that these sites were likely to evolve under positive selection. Moreover, a strong TATA "motif" was evident in the core region within the functional CArG elements in both human and mouse promoters. This motif could probably be a major contribution to the formation of the spatial structure, which was important for CArG-SRF recognition. Thus, the study further revealed the sequence character and substitution pattern of CArG elements and provided useful information for the study of the SRF-binding efficiencies of CArG promoters in functional assays.

A MADS-box transcription factor MoMcm1 is required for male fertility, microconidium production and virulence in Magnaporthe oryzae

Appressorium formation is a key step in the infection cycle of Magnaporthe oryzae. Mst12 is a transcription factor essential for appressorium penetration and invasive growth. In this study we used the affinity purification approach to identify proteins that physically associate with Mst12. One of the Mst12-interacting genes identified was MoMCM1, which encodes a MADS-box protein orthologous to yeast Mcm1. MoMcm1 interacted with both Mst12 and Mata-1 in yeast two-hybrid assays. Deletion of MoMCM1 resulted in the loss of male fertility and microconidium production. The Momcm1 mutant was defective in appressorium penetration and formed narrower invasive hyphae, which may be responsible for its reduced virulence. In transformants expressing MoMCM1-eGFP fusion, GFP signals were observed in the nucleus. We also generated the Momcm1 mst12 double mutant, which was defective in penetration and non-pathogenic. On hydrophilic surfaces, germ tubes produced by the double mutant were severely curved, and 20% of them formed appressoria. In contrast, the Momcm1 or mst12 mutant did not form appressoria on hydrophilic surfaces. These results suggest that MoMCM1 and MST12 have overlapping functions to suppress appressorium formation under non-conducive conditions. MoMcm1 may interact with Mst12 and MatA-1 to regulate germ tube identity and male fertility respectively.

The Dynamical Systems Properties of the HOG Signaling Cascade

The High Osmolarity Glycerol (HOG) MAP kinase pathway in the budding yeast Saccharomyces cerevisiae is one of the best characterized model signaling pathways. The pathway processes external signals of increased osmolarity into appropriate physiological responses within the yeast cell. Recent advances in microfluidic technology coupled with quantitative modeling, and techniques from reverse systems engineering have allowed yet further insight into this already well-understood pathway. These new techniques are essential for understanding the dynamical processes at play when cells process external stimuli into biological responses. They are widely applicable to other signaling pathways of interest. Here, we review the recent advances brought by these approaches in the context of understanding the dynamics of the HOG pathway signaling.

Lineage-based primary muscle fiber type diversification independent of MEF2 and NFAT in chick embryos

Differences in primary avian skeletal muscle fiber types are based on myoblast cell lineages and independent of innervation. To understand the basis for this mode of myogenesis, embryonic myoblasts specifically committed to the formation of either fast or fast/slow muscle fiber types were isolated, characterized, and examined for their capacities to transcriptionally regulate the slow myosin heavy chain 2 (MyHC2) gene. Myogenic basic helix-loop-helix protein binding sites within the slow MyHC2 promoter were mutated and did not direct fast versus fast/slow muscle fiber type development. Using promoter analyses coupled with overexpression studies and transcriptional sensors, the roles of Nuclear Factor of Activated T cells (NFATc1), and MEF2A in regulation of the slow MyHC2 gene were determined. MEF2A activated the slow MyHC2 promoter in both fast and fast/slow primary muscle fibers. In contrast, NFATc1 repressed promoter activity. These results do not support the roles of MEF2 and NFAT as direct regulators of primary muscle fiber type differences. Rather, the results reflect intrinsic differences in the modes of regulation of the slow MyHC2 gene in primary muscle fiber types.

cDNA cloning and characterization of 5' upstream promoter region of porcine mef2c gene

The myocyte enhancer factor 2C (MEF2C) is a member of the MEF2 family of transcription factors, involved in skeletal muscle development. In this study we report the cDNA sequence and isolate the 5' upstream region of the mef2c gene from porcine genomic DNA using PCR-based GenomeWalker. The open reading frame of porcine mef2c cDNA covers 1,392 bases, encoding 464 amino acids, which show 94% identity with human MEF2C at the level of the primary protein structure. Annear the C terminus of mef2c, a 96-nt sequence appear to represent alternatively spliced transcripts was present in some cDNAs and absent in the other. No typical TATA, GC box or CAAT box binding site was found in porcine mef2c 5' upstream region, whereas some potential binding sites for MyoD (E-box), MEF2 and MBF1 were present in the proximal upstream region. Transfection of the mef2c 5' upstream region with EGFP into cos7 cells demonstrated that the region from -162 to +115 bp immediately 5' of the exon 1 was sufficient to direct strong EGFP protein expression. Co-transfection assays demonstrated that MBF1 bound the mef2c promoter and inhibited mef2c expression. These results may be useful for elucidating the regulation mechanisms of mef2c, which interacts with other factors to regulate target genes.

Serum response factor utilizes distinct promoter- and enhancer-based mechanisms to regulate cytoskeletal gene expression in macrophages

Cells of the monocyte/macrophage lineage play essential roles in tissue homeostasis and immune responses, but mechanisms underlying the coordinated expression of cytoskeletal genes required for specialized functions of these cells, such as directed migration and phagocytosis, remain unknown. Here, using genetic and genomic approaches, we provide evidence that serum response factor (SRF) regulates both general and cell type-restricted components of the cytoskeletal gene expression program in macrophages. Genome-wide location analysis of SRF in macrophages demonstrates enrichment of SRF binding at ubiquitously expressed target gene promoters, as expected, but also reveals that the majority of SRF binding sites associated with cell type-restricted target genes are at distal inter- and intragenic locations. Most of these distal SRF binding sites are established by the prior binding of the macrophage- and the B cell-specific transcription factor PU.1 and exhibit histone modifications characteristic of enhancers. Consistent with this, representative cytoskeletal target genes associated with these elements require both SRF and PU.1 for full expression. These findings suggest that SRF uses two distinct molecular strategies to regulate programs of cytoskeletal gene expression: a promoter-based strategy for ubiquitously expressed target genes and an enhancer-based strategy at target genes that exhibit cell type-restricted patterns of expression.

Three MADS-box genes of Hevea brasiliensis expressed during somatic embryogenesis and in the laticifer cells

Three MADS-box genes, designated HbMADS1, HbMADS2 and HbMADS3, were isolated from Hevea brasiliensis. HbMADS1, HbMADS2 and HbMADS3 encode polypetides consisting of 245, 217 and 239 amino acids, respectively, containing conserved MADS-box motifs at N-terminus. Transcription pattern analysis revealed that three MADS-box genes had highly transcription in the laticifer cells. The transcriptions of HbMADS1and HbMADS3 were induced in the laticifer cells by jamonic acid, while HbMADS2 was not induction by jamonic acid. Ethephone is not effective in inducing their expression. The three genes were differentially expressed during somatic embryogenesis of rubber tree. Characterization of HbMADSs will attribute to understand their possible function in rubber tree.

Mutations in MEF2C from the 5q14.3q15 microdeletion syndrome region are a frequent cause of severe mental retardation and diminish MECP2 and CDKL5 expression

The etiology of mental retardation remains elusive in the majority of cases. Microdeletions within chromosomal bands 5q14.3q15 were recently identified as a recurrent cause of severe mental retardation, epilepsy, muscular hypotonia, and variable minor anomalies. By molecular karyotyping we identified two novel 2.4- and 1.5-Mb microdeletions of this region in patients with a similar phenotype. Both deletions contained the MEF2C gene, which is located proximally to the previously defined smallest region of overlap. Nevertheless, due to its known role in neurogenesis, we considered MEF2C as a phenocritical candidate gene for the 5q14.3q15 microdeletion phenotype. We therefore performed mutational analysis in 362 patients with severe mental retardation and found two truncating and two missense de novo mutations in MEF2C, establishing defects in this transcription factor as a novel relatively frequent autosomal dominant cause of severe mental retardation accounting for as much as 1.1% of patients. In these patients we found diminished MECP2 and CDKL5 expression in vivo, and transcriptional reporter assays indicated that MEF2C mutations diminish synergistic transactivation of E-box promoters including that of MECP2 and CDKL5. We therefore conclude that the phenotypic overlap of patients with MEF2C mutations and atypical Rett syndrome is due to the involvement of a common pathway.

Role of serum response factor in the pathogenesis of disease

Serum response factor (SRF) is a ubiquitously expressed transcription factor that binds to a DNA cis element known as the CArG box, which is found in the proximal regulatory regions of over 200 experimentally validated target genes. Genetic deletion of SRF is incompatible with life in a variety of animals from different phyla. In mice, loss of SRF throughout the early embryo results in gastrulation defects precluding analyses in individual organ systems. Genetic inactivation studies using conditional or inducible promoters directing the expression of the bacteriophage Cre recombinase have shown a vital role for SRF in such cellular processes as contractility, cell migration, synaptic activity, inflammation, and cell survival. A growing number of experimental and human diseases are associated with changes in SRF expression, suggesting that SRF has a role in the pathogenesis of disease. This review summarizes data from experimental model systems and human pathology where SRF expression is either deliberately or naturally altered.

Conservation and evolution in and among SRF- and MEF2-type MADS domains and their binding sites

Serum response factor (SRF) and myocyte enhancer factor 2 (MEF2) represent two types of members of the MCM1, AGAMOUS, DEFICIENS, and SRF (MADS)-box transcription factor family present in animals and fungi. Each type has distinct biological functions, which are reflected by the distinct specificities of the proteins bound to their cognate DNA-binding sites and activated by their respective cofactors. However, little is known about the evolution of MADS domains and their DNA-binding sites. Here, we report on the conservation and evolution of the two types of MADS domains with their cognate DNA-binding sites by using phylogenetic analyses. First, there are great similarities between the two types of proteins with amino acid positions highly conserved, which are critical for binding to the DNA sequence and for the maintenance of the 3D structure. Second, in contrast to MEF2-type MADS domains, distinct conserved residues are present at some positions in SRF-type MADS domains, determining specificity and the configuration of the MADS domain bound to DNA sequences. Furthermore, the ancestor sequence of SRF- and MEF2-type MADS domains is more similar to MEF2-type MADS domains than to SRF-type MADS domains. In the case of DNA-binding sites, the MEF2 site has a T-rich core in one DNA sequence and an A-rich core in the reverse sequence as compared with the SRF site, no matter whether where either A or T is present in the two complementary sequences. In addition, comparing SRF sites in the human and the mouse genomes reveals that the evolution rate of CArG-boxes is faster in mouse than in human. Moreover, interestingly, a CArG-like sequence, which is probably functionless, could potentially mutate to a functional CArG-box that can be bound by SRF and vice versa. Together, these results significantly improve our knowledge on the conservation and evolution of the MADS domains and their binding sites to date and provide new insights to investigate the MADS family, which is not only on evolution of MADS factors but also on evolution of their binding sites and even on coevolution of MADS factors with their binding sites.

Revisited and revised: is RhoA always a villain in cardiac pathophysiology?

The neonatal rat ventricular myocyte model of hypertrophy has provided tremendous insight with regard to signaling pathways regulating cardiac growth and gene expression. Many mediators thus discovered have been successfully extrapolated to the in vivo setting, as assessed using genetically engineered mice and physiological interventions. Studies in neonatal rat ventricular myocytes demonstrated a role for the small G-protein RhoA and its downstream effector kinase, Rho-associated coiled-coil containing protein kinase (ROCK), in agonist-mediated hypertrophy. Transgenic expression of RhoA in the heart does not phenocopy this response, however, nor does genetic deletion of ROCK prevent hypertrophy. Pharmacologic inhibition of ROCK has effects most consistent with roles for RhoA signaling in the development of heart failure or responses to ischemic damage. Whether signals elicited downstream of RhoA promote cell death or survival and are deleterious or salutary is, however, context and cell-type dependent. The concepts discussed above are reviewed, and the hypothesis that RhoA might protect cardiomyocytes from ischemia and other insults is presented. Novel RhoA targets including phospholipid regulated and regulating enzymes (Akt, PI kinases, phospholipase C, protein kinases C and D) and serum response element-mediated transcriptional responses are considered as possible pathways through which RhoA could affect cardiomyocyte survival.

Activation and repression of cellular immediate early genes by serum response factor cofactors

The induction of expression of many cellular immediate early genes (IEG) involves the transcription factor serum response factor (SRF). Two families of SRF coactivators have also been implicated in IEG induction, the ternary complex factors (TCFs), ELK1, Sap1, and Net, and the myocardin-related factors, MKL1 and MKL2. We found that serum induction of some SRF target genes is preferentially regulated by MKL1/2, whereas others are redundantly activated by both TCFs and MKL1/2. Yet ELK1 can also repress transcription. Binding of ELK1 and MKL1 to SRF has been found to be mutually exclusive in vitro, suggesting that ELK1 could repress expression of IEGs by blocking MKL1 binding. We characterized the in vivo binding of MKL1 and ELK1 to target genes and found an inverse relationship of serum-induced MKL1 binding and serum-decreased ELK1 binding. However, experiments with short hairpin RNA-mediated MKL1/2 depletion and expression of a nuclear MKL1 (N100) variant in stably transfected cells failed to alter ELK1 binding, suggesting that ELK1 binding to target genes is regulated independently of MKL1/2. Nevertheless, we found that short interfering RNA-mediated depletion of TCFs increased target gene expression in cells containing the N100 MKL1 activator, most notably in cells under continuous growth conditions. These results indicate that the TCFs can function both as activators and repressors of target gene expression depending upon the cellular growth conditions.

Linking actin dynamics and gene transcription to drive cellular motile functions

Numerous physiological and pathological stimuli promote the rearrangement of the actin cytoskeleton, thereby modulating cellular motile functions. Although it seems intuitively obvious that cell motility requires coordinated protein biosynthesis, until recently the linkage between cytoskeletal actin dynamics and correlated gene activities remained unknown. This knowledge gap was filled in part by the discovery that globular actin polymerization liberates myocardin-related transcription factor (MRTF) cofactors, thereby inducing the nuclear transcription factor serum response factor (SRF) to modulate the expression of genes encoding structural and regulatory effectors of actin dynamics. This insight stimulated research to better understand the actin-MRTF-SRF circuit and to identify alternative mechanisms that link cytoskeletal dynamics and genome activity.

Structure of the MADS-box/MEF2 domain of MEF2A bound to DNA and its implication for myocardin recruitment

Myocyte enhancer factor 2 (MEF2) regulates specific gene expression in diverse developmental programs and adaptive responses. MEF2 recognizes DNA and interacts with transcription cofactors through a highly conserved N-terminal domain referred to as the MADS-box/MEF2 domain. Here we present the crystal structure of the MADS-box/MEF2 domain of MEF2A bound to DNA. In contrast to previous structural studies showing that the MEF2 domain of MEF2A is partially unstructured, the present study reveals that the MEF2 domain participates with the MADS-box in both dimerization and DNA binding as a single domain. The sequence divergence at and immediately following the C-terminal end of the MEF2 domain may allow different MEF2 dimers to recognize different DNA sequences in the flanking regions. The current structure also suggests that the ligand-binding pocket previously observed in the Cabin1-MEF2B-DNA complex and the HDAC9 (histone deacetylase 9)-MEF2B-DNA complex is not induced by cofactor binding but rather preformed by intrinsic folding. However, the structure of the ligand-binding pocket does undergo subtle but significant conformational changes upon cofactor binding. On the basis of these observations, we generated a homology model of MEF2 bound to a myocardin family protein, MASTR, that acts as a potent coactivator of MEF2-dependent gene expression. The model shows excellent shape and chemical complementarity at the binding interface and is consistent with existing mutagenesis data. The apo structure presented here can also serve as a target for virtual screening and soaking studies of small molecules that can modulate the function of MEF2 as research tools and therapeutic leads.

MIKC* MADS-box proteins: conserved regulators of the gametophytic generation of land plants

Land plants (embryophytes) are characterized by an alternation of two generations, the haploid gametophyte and the diploid sporophyte. The development of the small and simple male gametophyte of the flowering plant Arabidopsis (Arabidopsis thaliana) critically depends on the action of five MIKC* group MCM1-AGAMOUS-DEFICIENS-SRF-box (MADS-box) proteins. In this study, these MIKC* MADS-box genes were isolated from land plants with relatively large and complex gametophyte bodies, namely the bryophytes. We found that although the gene family expanded in the mosses Sphagnum subsecundum, Physcomitrella patens, and Funaria hygrometrica, only a single homologue, Marchantia polymorpha MADS-box gene 1 (MpMADS1), has been retained in the liverwort M. polymorpha. Liverworts are the earliest diverging land plants, and so a comparison of MpMADS1 with its angiosperm homologues addresses the molecular evolution of an embryophyte-specific transcription factor over the widest phylogenetic distance. MpMADS1 was found to form a homodimeric DNA-binding complex, which is in contrast to the Arabidopsis proteins that are functional only as heterodimeric complexes. The M. polymorpha homodimer, nevertheless, recognizes the same DNA sequences as its angiosperm counterparts and can functionally replace endogenous MIKC* complexes to a significant extent when heterologously expressed in Arabidopsis pollen. The 11 MIKC* homologues from the moss F. hygrometrica are highly and almost exclusively expressed in the gametophytic generation. Taken together, these findings suggest that MIKC* MADS-box proteins have largely preserved molecular roles in the gametophytic generation of land plants.