KNUCKLES (KNU) encodes a C2H2 zinc-finger protein that regulates development of basal pattern elements of the Arabidopsis gynoecium

[Cloning and functional analysis of SCTF-1 encoding a C2H2-type Zinc finger protein from soybean]

The zinc finger protein is one of the proteins with finger-like domain. Some of them are transcription factors which play important role in plant growth and plant resistance to abiotic stresses. In this paper, a novel C2H2-type zinc finger protein gene SCTF-1 (GenBank accession number JQ692081) was isolated from soybean (Glycine max (L.) Merr.) This gene has a 699 bp ORF (open reading frame) with no intron and encodes a 24.9 kDa protein with 233 amino acids. Its isoelectric point (pI) is 8.33. The SCTF-1 protein contains two typical C2H2-type zinc finger domains. Both of them have highly conserved amino acid sequence-QALGGH which is a particular characteristic of plant. Transient expression of the GFP-SCTF-1 protein in onion epidermal cell showed that SCTF-1 was localized in cell nuclei. RT-PCR results showed that SCTF-1 gene was expressed with high levels in flowers and leaves in soybean, but low in roots and stems. The expression of SCTF-1 gene was strongly induced by low temperature in the soybean seedlings. Overexpression of SCTF-1 enhanced cold tolerance of transgenic tobacco (Nicotiana tabacum L.) compared to the control.

Somatic small RNA pathways promote the mitotic events of megagametogenesis during female reproductive development in Arabidopsis

Female gamete development in Arabidopsis ovules comprises two phases. During megasporogenesis, a somatic ovule cell differentiates into a megaspore mother cell and undergoes meiosis to produce four haploid megaspores, three of which degrade. The surviving functional megaspore participates in megagametogenesis, undergoing syncytial mitosis and cellular differentiation to produce a multicellular female gametophyte containing the egg and central cell, progenitors of the embryo and endosperm of the seed. The transition between megasporogenesis and megagametogenesis is poorly characterised, partly owing to the inaccessibility of reproductive cells within the ovule. Here, laser capture microdissection was used to identify genes expressed in and/or around developing megaspores during the transition to megagametogenesis. ARGONAUTE5 (AGO5), a putative effector of small RNA (sRNA) silencing pathways, was found to be expressed around reproductive cells during megasporogenesis, and a novel semi-dominant ago5-4 insertion allele showed defects in the initiation of megagametogenesis. Expression of a viral RNAi suppressor, P1/Hc-Pro, driven by the WUSCHEL and AGO5 promoters in somatic cells flanking the megaspores resulted in a similar phenotype. This indicates that sRNA-dependent pathways acting in somatic ovule tissues promote the initiation of megagametogenesis in the functional megaspore. Notably, these pathways are independent of AGO9, which functions in somatic epidermal ovule cells to inhibit the formation of multiple megaspore-like cells. Therefore, one somatic sRNA pathway involving AGO9 restricts reproductive development to the functional megaspore and a second pathway, inhibited by ago5-4 and P1/Hc-Pro, promotes megagametogenesis.

LATE, a C(2)H(2) zinc-finger protein that acts as floral repressor

The transition from vegetative to generative development is a major developmental switch in flowering plants and is critical for reproductive success. This transition requires reprogramming of lateral primordia at the shoot apical meristem, which leads to the formation of determinate floral meristems instead of leaves. In Arabidopsis, flowering is induced by a network of interacting pathways. In the photoperiod-dependent pathway, the two key elements mediating the effect of day length on flowering time are the transcription factors CONSTANS (CO) and the phloem mobile flowering signal FLOWERING LOCUS T (FT). Here, we identify a factor that is critically involved in this flowering response. The gene, which we named LATE FLOWERING (LATE), encodes a C(2)H(2) -type zinc-finger transcriptional regulator, and is expressed in the leaf vasculature and the vegetative shoot apical meristem. Ectopic expression of LATE in all tissues results in a dose-dependent phenotype characterized by late flowering, altered floral organ identity and sterile flowers. Using tissue-specific promoters, we further show that LATE controls the transition to flowering at two levels: first, it regulates the expression of flowering time genes in the leaf vasculature, and second, it interferes with floral meristem identity genes at the apex.

Parthenocarpic potential in Capsicum annuum L. is enhanced by carpelloid structures and controlled by a single recessive gene

BACKGROUND

Parthenocarpy is a desirable trait in Capsicum annuum production because it improves fruit quality and results in a more regular fruit set. Previously, we identified several C. annuum genotypes that already show a certain level of parthenocarpy, and the seedless fruits obtained from these genotypes often contain carpel-like structures. In the Arabidopsis bel1 mutant ovule integuments are transformed into carpels, and we therefore carefully studied ovule development in C. annuum and correlated aberrant ovule development and carpelloid transformation with parthenocarpic fruit set.

RESULTS

We identified several additional C. annuum genotypes with a certain level of parthenocarpy, and confirmed a positive correlation between parthenocarpic potential and the development of carpelloid structures. Investigations into the source of these carpel-like structures showed that while the majority of the ovules in C. annuum gynoecia are unitegmic and anatropous, several abnormal ovules were observed, abundant at the top and base of the placenta, with altered integument growth. Abnormal ovule primordia arose from the placenta and most likely transformed into carpelloid structures in analogy to the Arabidopsis bel1 mutant. When pollination was present fruit weight was positively correlated with seed number, but in the absence of seeds, fruit weight proportionally increased with the carpelloid mass and number. Capsicum genotypes with high parthenocarpic potential always showed stronger carpelloid development. The parthenocarpic potential appeared to be controlled by a single recessive gene, but no variation in coding sequence was observed in a candidate gene CaARF8.

CONCLUSIONS

Our results suggest that in the absence of fertilization most C. annuum genotypes, have parthenocarpic potential and carpelloid growth, which can substitute developing seeds in promoting fruit development.

AGAMOUS terminates floral stem cell maintenance in Arabidopsis by directly repressing WUSCHEL through recruitment of Polycomb Group proteins

Floral stem cells produce a defined number of floral organs before ceasing to be maintained as stem cells. Therefore, floral stem cells offer an ideal model to study the temporal control of stem cell maintenance within a developmental context. AGAMOUS (AG), a MADS domain transcription factor essential for the termination of floral stem cell fate, has long been thought to repress the stem cell maintenance gene WUSCHEL (WUS) indirectly. Here, we uncover a role of Polycomb Group (PcG) genes in the temporally precise repression of WUS expression and termination of floral stem cell fate. We show that AG directly represses WUS expression by binding to the WUS locus and recruiting, directly or indirectly, PcG that methylates histone H3 Lys-27 at WUS. We also show that PcG acts downstream of AG and probably in parallel with the known AG target KNUCKLES to terminate floral stem cell fate. Our studies identify core components of the network governing the temporal program of floral stem cells.

Zinc finger protein5 is required for the control of trichome initiation by acting upstream of zinc finger protein8 in Arabidopsis

Arabidopsis (Arabidopsis thaliana) trichome development is a model system for studying cell development, cell differentiation, and the cell cycle. Our previous studies have shown that the GLABROUS INFLORESCENCE STEMS (GIS) family genes, GIS, GIS2, and ZINC FINGER PROTEIN8 (ZFP8), control shoot maturation and epidermal cell fate by integrating gibberellins (GAs) and cytokinin signaling in Arabidopsis. Here, we show that a new C2H2 zinc finger protein, ZFP5, plays an important role in controlling trichome cell development through GA signaling. Overexpression of ZFP5 results in the formation of ectopic trichomes on carpels and other inflorescence organs. zfp5 loss-of-function mutants exhibit a reduced number of trichomes on sepals, cauline leaves, paraclades, and main inflorescence stems in comparison with wild-type plants. More importantly, it is found that ZFP5 mediates the regulation of trichome initiation by GAs. These results are consistent with ZFP5 expression patterns and the regional influence of GA on trichome initiation. The molecular analyses suggest that ZFP5 functions upstream of GIS, GIS2, ZFP8, and the key trichome initiation regulators GLABROUS1 (GL1) and GL3. Using a steroid-inducible activation of ZFP5 and chromatin immunoprecipitation experiments, we further demonstrate that ZFP8 is the direct target of ZFP5 in controlling epidermal cell differentiation.

Coordination of flower development by homeotic master regulators

Floral homeotic genes encode transcription factors and act as master regulators of flower development. The homeotic protein complex is expressed in a specific whorl of the floral primordium and determines floral organ identity by the combinatorial action. Homeotic proteins continue to be expressed until late in flower development to coordinate growth and organogenesis. Recent genomic studies have shown that homeotic proteins bind thousands of target sites in the genome and regulate the expression of transcription factors, chromatin components and various proteins involved in hormone biosynthesis and signaling and other physiological activities. Further, homeotic proteins program chromatin to direct the developmental coordination of stem cell maintenance and differentiation in shaping floral organs.

Arabidopsis and Tobacco superman regulate hormone signalling and mediate cell proliferation and differentiation

Arabidopsis thaliana superman (SUP) plays an important role during flower development by maintaining the boundary between stamens and carpels in the inner two whorls. It was proposed that SUP maintains this boundary by regulating cell proliferation in both whorls, as loss-of-function superman mutants produce more stamens at the expense of carpels. However, the cellular mechanism that underlies SUP function remains unknown. Here Arabidopsis or tobacco (Nicotiana tabacum) SUP was overexpressed in tobacco plants to substantiate SUP's role as a regulator of cell proliferation and boundary definition and provide evidence that its biological role may be mediated via hormonal changes. It was found that moderate levels of SUP stimulated cell growth and proliferation, whereas high levels were inhibitory. SUP stimulated auxin- and cytokinin-regulated processes, and cells overexpressing SUP displayed reduced hormone dependency for proliferation and regeneration into plants. SUP also induced proliferation of female traits in the second and third flower whorls and promoted differentiation of petaloid properties in sepals, further supporting a role for SUP as a boundary regulator. Moreover, cytokinin suppressed stamen development and promoted differentiation of carpeloid tissues, suggesting that SUP may regulate male and female development via its effect on cytokinin signalling. Taken together, these observations suggest a model whereby the effect of SUP on cell growth and proliferation involves the modulation of auxin- and cytokinin-regulated processes. Furthermore, differential SUP expression or different sensitivities of different cell types to SUP may determine whether SUP stimulates or suppresses their proliferation.

Ovule is a lateral organ finally differentiated from the terminating floral meristem in rice

The floral meristem is the homeostatic source of floral organs in angiosperms. In rice, after stamen and carpel differentiation, the floral meristem is terminated and exhausted to produce an ovule. To elucidate underlying mechanisms controlling the continuous process from floral meristem termination to ovule formation, we investigated two rice mutants showing abnormalities in ovule formation. In the weak mutant of the lonely guy gene, responsible for cytokinin activation to maintain the floral meristem, ovule formation was abolished inside the normally developing carpel. The loss-of-function of the OsMADS13 gene, encoding a MADS-box transcription factor, resulted in the replacement of ovule with extra carpels. The in situ expression of tissue-specific markers in both mutants revealed that a lateral region of the terminating floral meristem adjacent to the site of carpel initiation exclusively differentiated the ovule and is apparently distinct from the remainder of the floral meristem, in contrast to previous assumptions. Our findings also suggest that primordial germ cells are initiated independently of ovule formation, but dependently on the presence of active cytokinin. We propose a novel pattern of ovule formation in angiosperms, in which the ovule is a lateral organ finally differentiated from the terminating floral meristem in rice.

Floral stem cells: from dynamic balance towards termination

During early flower development in Arabidopsis, floral stem cells proliferate and produce a sufficient amount of cells that are recruited for organogenesis. However, after the central organ primordia initiate, stem cell activity in the floral meristem is terminated to ensure the differentiation of a fixed number of floral organs. Underlying this process, the genetic programme regulating the fate of floral meristems undergoes a shift from a spatially balanced signalling scheme for stem cell maintenance to a temporally controlled transcriptional scheme for stem cell termination. Precise timing of stem cell termination is a key issue for flower development, which is secured by the orchestration of multiple regulators in transcriptional and epigenetic regulation.

Flower development

Flowers are the most complex structures of plants. Studies of Arabidopsis thaliana, which has typical eudicot flowers, have been fundamental in advancing the structural and molecular understanding of flower development. The main processes and stages of Arabidopsis flower development are summarized to provide a framework in which to interpret the detailed molecular genetic studies of genes assigned functions during flower development and is extended to recent genomics studies uncovering the key regulatory modules involved. Computational models have been used to study the concerted action and dynamics of the gene regulatory module that underlies patterning of the Arabidopsis inflorescence meristem and specification of the primordial cell types during early stages of flower development. This includes the gene combinations that specify sepal, petal, stamen and carpel identity, and genes that interact with them. As a dynamic gene regulatory network this module has been shown to converge to stable multigenic profiles that depend upon the overall network topology and are thus robust, which can explain the canalization of flower organ determination and the overall conservation of the basic flower plan among eudicots. Comparative and evolutionary approaches derived from Arabidopsis studies pave the way to studying the molecular basis of diverse floral morphologies.

Genome-wide analysis of ethylene-responsive element binding factor-associated amphiphilic repression motif-containing transcriptional regulators in Arabidopsis

The ethylene-responsive element binding factor-associated amphiphilic repression (EAR) motif is a transcriptional regulatory motif identified in members of the ethylene-responsive element binding factor, C2H2, and auxin/indole-3-acetic acid families of transcriptional regulators. Sequence comparison of the core EAR motif sites from these proteins revealed two distinct conservation patterns: LxLxL and DLNxxP. Proteins containing these motifs play key roles in diverse biological functions by negatively regulating genes involved in developmental, hormonal, and stress signaling pathways. Through a genome-wide bioinformatics analysis, we have identified the complete repertoire of the EAR repressome in Arabidopsis (Arabidopsis thaliana) comprising 219 proteins belonging to 21 different transcriptional regulator families. Approximately 72% of these proteins contain a LxLxL type of EAR motif, 22% contain a DLNxxP type of EAR motif, and the remaining 6% have a motif where LxLxL and DLNxxP are overlapping. Published in vitro and in planta investigations support approximately 40% of these proteins functioning as negative regulators of gene expression. Comparative sequence analysis of EAR motif sites and adjoining regions has identified additional preferred residues and potential posttranslational modification sites that may influence the functionality of the EAR motif. Homology searches against protein databases of poplar (Populus trichocarpa), grapevine (Vitis vinifera), rice (Oryza sativa), and sorghum (Sorghum bicolor) revealed that the EAR motif is conserved across these diverse plant species. This genome-wide analysis represents the most extensive survey of EAR motif-containing proteins in Arabidopsis to date and provides a resource enabling investigations into their biological roles and the mechanism of EAR motif-mediated transcriptional regulation.

The flowering of Arabidopsis flower development

Flowers come in a variety of colors, shapes and sizes. Despite this variety, flowers have a very stereotypical architecture, consisting of a series of sterile organs surrounding the reproductive structures. Arabidopsis, as the premier model system for molecular and genetic analyses of plant development, has provided a wealth of insights into how this architecture is specified. With the advent of the completion of the Arabidopsis genome sequence a decade ago, in combination with a rich variety of forward and reverse genetic strategies, many of the genes and regulatory pathways controlling flower initiation, patterning, growth and differentiation have been characterized. A central theme that has emerged from these studies is the complexity and abundance of both positive and negative feedback loops that operate to regulate different aspects of flower formation. Presumably, this considerable degree of feedback regulation serves to promote a robust and stable transition to flowering, even in the face of genetic or environmental perturbations. This review will summarize recent advances in defining the genes, the regulatory pathways, and their interactions, that underpin how the Arabidopsis flower is formed.

AGAMOUS controls GIANT KILLER, a multifunctional chromatin modifier in reproductive organ patterning and differentiation

The floral, homeotic protein AGAMOUS coordinates multiple downstream genes through direct transcriptional regulation of the nuclear matrix attachment region binding protein GIANT KILLER.

The Arabidopsis homeotic protein AGAMOUS (AG), a MADS domain transcription factor, specifies reproductive organ identity during flower development. Using a binding assay and expression analysis, we identified a direct target of AG, GIANT KILLER (GIK), which fine-tunes the expression of multiple genes downstream of AG. The GIK protein contains an AT-hook DNA binding motif that is widely found in chromosomal proteins and that binds to nuclear matrix attachment regions of DNA elements. Overexpression and loss of function of GIK cause wide-ranging defects in patterning and differentiation of reproductive organs. GIK directly regulates the expression of several key transcriptional regulators, including ETTIN/AUXIN RESPONSE FACTOR 3 (ETT/ARF3) that patterns the gynoecium, by binding to the matrix attachment regions of target promoters. Overexpression of GIK causes a swift and dynamic change in repressive histone modification in the ETT promoter. We propose that GIK acts as a molecular node downstream of the homeotic protein AG, regulating patterning and differentiation of reproductive organs through chromatin organization.

Multicellular development depends on proper expression of thousands of genes. Master regulators, such as homeotic proteins, code for transcription factors in both plants and animals and are thought to act by regulating other genes. Recent genomic studies in the plant Arabidopsis have shown that over 1,000 genes are regulated by homeotic proteins that directly control various target genes, including different classes of transcriptional regulators. It is not known, however, how expression of so many genes is coordinated by a single homeotic gene to form functional organs and tissues. Here we identified a transcriptional target of the plant homeotic protein AGAMOUS using bioinformatics analysis and showed that AGAMOUS directly controls GIANT KILLER, a multifunctional chromatin modifier. GIANT KILLER then binds to the upstream regions of multiple genes involved in patterning and differentiation in the AGAMOUS pathway and fine-tunes the expression of these genes. These data therefore provide a possible mechanism by which a homeotic gene coordinates multiple downstream targets in plants.

A timing mechanism for stem cell maintenance and differentiation in the Arabidopsis floral meristem

Developmental regulation of the floral meristem ensures that plants of the same species have similarly sized flowers with a fixed number of floral organs. The maintenance of stem cells in the floral meristem is terminated after the production of a fixed number of floral organ primordia. Precise repression of the Arabidopsis thaliana homeobox gene WUSCHEL (WUS) by the floral homeotic protein AGAMOUS (AG) plays a major part in this process. Here we show that KNUCKLES (KNU) mediates the repression of WUS in floral meristem determinacy control. AG directly induces the transcription of KNU, which encodes a C2H2-type zinc finger protein with a conserved transcriptional repression motif. In turn, KNU represses WUS transcription to abolish stem cell activity. We also show that the timing of KNU induction is key in balancing proliferation and differentiation in flower development. Delayed KNU expression results in an indeterminate meristem, whereas ectopic KNU expression prematurely terminates the floral meristem. Furthermore, KNU induction by AG is preceded by changes in repressive histone modification at the KNU locus, which occurs in an AG-dependent manner. This study provides a mechanistic link between transcriptional feedback and epigenetic regulation in plant stem cell proliferation.

A terminator of floral stem cells

Normal flower development requires the termination of stem cell activities in the floral meristem. The floral regulator AGAMOUS (AG) is necessary for this termination and represses the expression of the stem cell determinant WUSCHEL (WUS), but the repression mechanism was not clear. A recent study by Sun and colleagues (pp. 1791-1804) in this issue of Genes & Development has identified a direct target of AG, KNUCKLES (KNU), which encodes a transcriptional repressor of WUS, providing a key missing link in floral meristem determinacy.

Identification of transcription factors predominantly expressed in soybean flowers and characterization of GmSEP1 encoding a SEPALLATA1-like protein

By microarray analysis and real-time RT-PCR, we identified 28 soybean flower-enriched transcription factors such as MADS-box proteins, zinc finger proteins, and MYB proteins. Among them, one MADS-box protein GmSEP1 was chosen for further analysis. GmSEP1 contains 8 exons and 7 introns, showing similar exon-intron structure with Arabidopsis SEP genes. Phylogenetic analysis also suggested that GmSEP1 belonged to AGL2/SEP subfamily and likely a soybean orthologue of Arabidopsis SEP1. Subcellular localization assay suggested that GmSEP1 was localized in nucleus. Semi-quantitative RT-PCR showed that GmSEP1 was predominantly expressed in reproductive organs including petal, sepal, stamen, carpel and seed. By real-time RT-PCR, we found that GmSEP1 was expressed with a low level in stamens of soybean mutant NJS-10Hfs in which some stamens are converted to petal-like structure. Further we found that expression of GmSEP1 was altered during the course of seed development and more accumulated in outer and inner integuments, epidermis and endothelium at the globular stage, heart stage and cotyledon stage and in seed coat parenchyma at the early maturation stage of seed development. Taken together, GmSEP1 might play important role in soybean reproductive development, in particular, in petal and seed coat development.

The NGATHA distal organ development genes are essential for style specification in Arabidopsis

Floral organ identities are specified by a few transcription factors that act as master regulators. Subsequently, specification of organ axes programs the distribution of distinct tissue types within the organs that themselves develop unique identities. The C-class, AGAMOUS-clade MADS box genes are primary promoters of the gynoecium, which is divided into a distal style and a subtending ovary along the apical-basal axis. We show that members of a clade of B3 domain transcription factors, NGATHA1 (NGA1) to NGA4, are expressed distally in all lateral organs, and all four have a redundant and essential role in style development. Loss of all four genes results in gynoecia where style is replaced by valve-like projections and a reduction in style-specific SHATTERPROOF1 (SHP1) expression. In agreement, floral misexpression of NGA1 promotes ectopic style and SHP1 expression. STYLISH1, an auxin biosynthesis inducer, conditionally activated NGA genes, which in turn promoted distal expression of other STY genes in a putative positive feedback loop. Inhibited auxin transport or lack of YABBY1 gene activities resulted in a basally expanded style domain and broader expression of NGA genes. We speculate that early gynoecium factors delimit NGA gene response to an auxin-based signal, elicited by STY gene activity, to restrict the activation of style program to a late and distal carpel domain.

Meristem activity during flower and ovule development in tomato is controlled by the mini zinc finger gene INHIBITOR OF MERISTEM ACTIVITY

Plants have the ability to form new organs as a result of indeterminate growth ensured by specific regions of pluripotent cells, called meristems. Flowers are produced by the activity of floral meristems which differ from vegetative meristems in their determinate fate. Transcriptional complexes associating C-, D- and E-type MADS box proteins are responsible for flower determinacy by controlling the stem cell population within the floral meristem. We report here that the INHIBITOR OF MERISTEM ACTIVITY (IMA) gene encoding a mini zinc finger (MIF) protein from tomato (Solanum lycopersicum) regulates the processes of flower and ovule development. IMA inhibits cell proliferation during floral termination, controls the number of carpels during floral development and acts as a repressor of the meristem organizing centre gene WUSCHEL. Underexpression of IMA prevents the formation of gametophytic tissue, which is replaced by an undetermined sporophytic tissue. Molecular analyses of MADS box gene expression revealed that IMA participates in the termination of floral meristems and initiation of ovule primordia by activating D-type gene expression. Taken together, our data indicate that both termination of floral meristems and differentiation of nucelli during ovule development require a similar mechanism involving the repression of WUSCHEL and the activation of D-class genes.

Characterization of genes controlling stamen identity and development in a parthenocarpic tomato mutant indicates a role for the DEFICIENS ortholog in the control of fruit set

The development of the ovary into a fruit depends on pollination and fertilization. It has been proposed that the restriction of ovary growth before pollination is because of the stamens acting as negative regulators. Accordingly, the silencing of genes responsible for stamen identity has been correlated with parthenocarpy in different species. The tomato (Solanum lycopersicum L.) parthenocarpic fruit (pat) mutation associates autonomous ovary development with homeotic transformation of the anthers and aberrancy of ovules in the ovary. In this study, we tested the hypothesis that stamen aberrations and parthenocarpy in pat are driven by cues coming from the altered expression of class B MADS box genes. The data showed that the Pat locus is not allelic to either of the two tomato mutations putatively involved in the B function, stamenless (sl)-2 and pistillate (pi) or to genes encoding class B transcription factors. Whereas pat pi double mutants were not recovered because of tight linkage, pat sl-2 double mutants showed mainly epistatic effects. The developmental regulation of the Sl DEFICIENS (DEF) gene in the wild-type (WT) at anthesis as well as its differential transcription in the pat ovary suggest that it plays a role in the control of ovary growth. Accordingly, when compared with the WT, the gene was also differentially expressed in the parthenocarpic fruit-2 (pat-2) mutant, that is not allelic to pat and has normal ovule development. Altogether the results indicate that in tomato SlDEF plays a role in the control of ovary growth and that the pat mutation is located upstream of this regulatory cascade.

GmZFP1 encoding a single zinc finger protein is expressed with enhancement in reproductive organs and late seed development in soybean (Glycine max)

The plant TFIIIA zinc finger proteins play important roles in plant growth and development. In this report, we isolated a single zinc finger gene, designated as GmZFP1, from soybean flowers by in silico mRNA subtraction strategy and RT-PCR. GmZFP1 is an intronless gene and encodes a protein of 210 amino acid residues with a predicted molecular mass of 23.5 KDa. GmZFP1 contains a single zinc finger domain and a DLN-box/EAR-motif at the C-terminus. To localize GmZFP1 mRNA in various tissues, semi-quantative RT-PCR assay was performed. GmZFP1 is expressed in all detected reproductive organs including flowers, developing seeds, pods, sepals, pistils with a low level, and more accumulated in petals, stamens, but not found in all detected vegetative organs with except of stem tips. Further, we found that the expression of GmZFP1 was higher in late seed development than in early seed development. To our knowledge, GmZFP1 is the first characterized gene encoding for single zinc finger protein in soybean, and may play a role as a transcriptional factor in reproductive organs development, especially functioning in petals, stamens and late developing seeds.

GLABROUS INFLORESCENCE STEMS modulates the regulation by gibberellins of epidermal differentiation and shoot maturation in Arabidopsis

As a plant shoot matures, it transitions through a series of growth phases in which successive aerial organs undergo distinct developmental changes. This process of phase change is known to be influenced by gibberellins (GAs). We report the identification of a putative transcription factor, GLABROUS INFLORESCENCE STEMS (GIS), which regulates aspects of shoot maturation in Arabidopsis thaliana. GIS loss-of-function mutations affect the epidermal differentiation of inflorescence organs, causing a premature decrease in trichome production on successive leaves, stem internodes, and branches. Overexpression has the opposite effect on trichome initiation and causes other heterochronic phenotypes, affecting flowering and juvenile-adult leaf transition and inducing the formation of rosette leaves on inflorescence stems. Genetic and gene expression analyses suggest that GIS acts in a GA-responsive pathway upstream of the trichome initiation regulator GLABROUS1 (GL1) and downstream of the GA signaling repressor SPINDLY (SPY). GIS mediates the induction of GL1 expression by GA in inflorescence organs and is antagonized in its action by the DELLA repressor GAI. The implication of GIS in the broader regulation of phase change is further suggested by the delay in flowering caused by GIS loss of function in the spy background. The discovery of GIS reveals a novel mechanism in the control of shoot maturation, through which GAs regulate cellular differentiation in plants.